MECHIR BANDA TEAM (MBT): COMPUTER NETWORKS CS610 book

<b><span style="font-size: large;">Computer Network BIT710/COMPUTER NETWORKS CS610 book HANDOUTS in pdf</span></b><br /><br />Handouts | Lectures | Contents | Books<div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
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COMPUTER NETWORKS</div>
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(CS610)</div>
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HANDOUTS</div>
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LECTURERS # 01 – 45</div>
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PREPARED BY:</div>
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HAMMAD KHALID KHAN</div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
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Table of contents</div>
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Lecture No. 1 .........................................................................................................4</div>
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INTRODUCTION ...........................................................................................................4</div>
<div>
Lecture No. 2 .........................................................................................................9</div>
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Motivation and Tools......................................................................................................9</div>
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Lecture No. 3 .......................................................................................................13</div>
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Overview of Data Communication ...............................................................................13</div>
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Lecture No. 4 .......................................................................................................14</div>
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PACKETS, FRAMES AND ERROR DETECTION.......................................................14</div>
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PACKETS AND TDM:...........................................................................................15</div>
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Figure 4.2 illustration of TDM.......................................................................................16</div>
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Lecture No. 5 .......................................................................................................17</div>
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BYTE STUFFING ........................................................................................................17</div>
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Lecture No. 6 .......................................................................................................22</div>
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SHIFT OPERATION ....................................................................................................22</div>
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Lecture No. 7 .......................................................................................................24</div>
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GROWTH OF LAN TECHNOLOGY ............................................................................24</div>
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Lecture No. 8 .......................................................................................................28</div>
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CARRIER SENSE MULTIPLE ACCESS (CSMA) .......................................................28</div>
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Lecture No. 9 .......................................................................................................33</div>
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HARDWARE ADDRESSING .......................................................................................33</div>
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Lecture No. 10 .....................................................................................................35</div>
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FRAME TYPE IDENTIFICATION ................................................................................35</div>
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Lecture No. 11 .....................................................................................................39</div>
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INTERFACE HARDWARE ..........................................................................................39</div>
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Lecture No. 12 .....................................................................................................43</div>
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LAN WIRING AND PHYSICAL TOPOLOGY...............................................................43</div>
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Lecture No. 13 .....................................................................................................48</div>
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FIBER MODEMS AND REPEATOERS.......................................................................48</div>
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Lecture No. 14 .....................................................................................................51</div>
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BRIDGES.....................................................................................................................51</div>
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Lecture No. 15 .....................................................................................................54</div>
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SWITCHES AND WAN TECHNOLOGIES ..................................................................54</div>
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Lecture No. 16 .....................................................................................................58</div>
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ROUTING ....................................................................................................................58</div>
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Lecture No. 17 .....................................................................................................62</div>
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ROUTING ALGORITHMS ...........................................................................................62</div>
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Lecture No. 18 .....................................................................................................66</div>
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CONNECTION-ORIENTED NETWORKING AND ATM..............................................66</div>
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Lecture No. 19 .....................................................................................................68</div>
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ATM: VIRTUAL CIRCUITS ..........................................................................................68</div>
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Lecture No. 20 .....................................................................................................72</div>
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ATM AND NETWORK OWNERSHIP ..........................................................................72</div>
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Lecture No. 21 .....................................................................................................75</div>
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NETWORK SERVICE PARADIGM .............................................................................75</div>
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Lecture No. 22 .....................................................................................................79</div>
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NETWORK PERFORMANCE .....................................................................................79</div>
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Lecture No. 23 .....................................................................................................81</div>
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INTERNETWORKING: CONCEPTS, ARCHITECTURE AND PROTOCOLS............81</div>
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Lecture No. 24 .....................................................................................................85</div>
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IP: INTERNET PROTOCOL ADDRESSES .................................................................85</div>
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Lecture No. 25 .....................................................................................................87</div>
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INTERNET PROTOCOL ADDRESS NOTATIONS .....................................................87</div>
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Lecture No. 26 .....................................................................................................90</div>
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IP SUBNETING ...........................................................................................................90</div>
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Lecture No. 27 .....................................................................................................93</div>
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ADDRESS REOLUTION PROTOCOL (ARP)..............................................................93</div>
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Lecture No. 28 .....................................................................................................97</div>
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ARP MESSAGE FORMAT ..........................................................................................97</div>
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Lecture No. 29 ...................................................................................................101</div>
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IP DATAGRAMS AND DATAGRAM FORWARDING................................................101</div>
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Lecture No. 30 ...................................................................................................105</div>
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IP ENCAPSULATION, FRAGMENTATION AND REASSEMBLY.............................105</div>
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Lecture No. 31 ...................................................................................................110</div>
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THE FUTURE IP (IPV6) ............................................................................................110</div>
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Lecture No. 32 ...................................................................................................113</div>
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IPv6 AND AN ERROR REPORTING MECHANISM..................................................113</div>
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Lecture No. 33 ...................................................................................................117</div>
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AN ERROR REPORTING MECHANISM (ICMP) ......................................................117</div>
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Lecture No. 34 ...................................................................................................119</div>
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UDP: DATAGRAM TRANSPORT SERVICE.............................................................119</div>
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Lecture No. 35 ...................................................................................................122</div>
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DATAGRAM FORMAT AND TCP: RELIABLE TRANSPORT SERVICE ..................122</div>
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Lecture No. 36 ...................................................................................................125</div>
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TCP: RELIABLE TRANSPORT SERVICE (Cont.).....................................................125</div>
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Lecture No. 37 ...................................................................................................128</div>
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NETWORK ADDRESS TRANSLATION (NAT) .........................................................128</div>
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Lecture No. 38 ...................................................................................................131</div>
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NETWORK ADDRESS TRANSLATION....................................................................131</div>
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Lecture No. 39 ...................................................................................................133</div>
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IP ROUTING (Part-1).................................................................................................133</div>
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Lecture No. 40 ...................................................................................................135</div>
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IP ROUTING (Part-2).................................................................................................135</div>
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Lecture No. 41 ...................................................................................................137</div>
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IP ROUTING (Part-3).................................................................................................137</div>
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Lecture No. 42 ...................................................................................................139</div>
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IP ROUTING (Part-4).................................................................................................139</div>
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Lecture No. 43 ...................................................................................................142</div>
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IP ROUTING (Part-5).................................................................................................142</div>
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Lecture No. 44 ...................................................................................................144</div>
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IP ROUTING (Part-6).................................................................................................144</div>
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Lecture No. 45 ...................................................................................................147</div>
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COURSE REVISION .................................................................................................147</div>
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Lecture No. 1</div>
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INTRODUCTION</div>
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NETWORK:</div>
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A network is defined as a system for connecting computers using a single</div>
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transmission technology. The computers can communicate with each other in a network.</div>
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They can send and receive data from each other when they are in a network.</div>
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INTERNET:</div>
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The Internet is defined as the set of networks connected by routers that</div>
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are configured to pass traffic among any computers attached to any network in the set. By</div>
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internet many computers which are at longer distances from each other can communicate</div>
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with each other.</div>
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CLASSIFICATION OF NETWORKS</div>
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Computer networks are classified by four factors which are as follow:</div>
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1) BY SIZE:</div>
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2) BY CONNECTIVITY:</div>
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3) BY MEDIUM:</div>
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4) BY MOBILITY:</div>
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1) BY SIZE:</div>
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According to their size there are two classifications of networks.</div>
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1. Local Area Network. ( LAN)</div>
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2. Wide Area Network (WAN)</div>
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In LAN network occupies the smaller area like a room a floor or a building.</div>
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In WAN, network occupies larger areas like cities & countries. Internet is a Wide Area</div>
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Network.</div>
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LAN & WAN are compared by the speed of transmission, bandwidth and</div>
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latency, management, security, reliability, billing and their standards.</div>
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2) BY CONNECTIVITY:</div>
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Networks are also classified by connectivity in which two topologies are discussed.</div>
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a) Point-to-Point</div>
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b) Broadcast</div>
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a) POINT-TO-POINT:</div>
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In Point-to-Point topology there are two topologies.</div>
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1) STAR topology</div>
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2) TREE topology</div>
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In star topology each computer is connected to a central hub. The communication</div>
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takes place through the hub. It is shown in the figure below.</div>
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Error!</div>
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Figure 1.1: star and tree topologies</div>
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In Tree topology all computers are connected to each other in such a way that they</div>
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make a tree as shown in the figure above.</div>
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b) BROADCAST:</div>
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In broadcast topology there are further two categories</div>
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1) SATELLITE\RADIO 2) RING TOPOLOGY</div>
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In a satellite or radio topology all computers are connected to each other via</div>
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satellite or radio wave as shown in the figure.</div>
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Star</div>
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Tree</div>
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Figure: 1.2 Satellite and Ring topologies: In a ring topology each computer is connected to other</div>
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thorough a ring as shown in the figure above.</div>
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3) BY MEDIUM:</div>
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The classification of networks is also based on the Medium of transmission.</div>
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Following are the mediums of transmission:</div>
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• Copper wire</div>
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• Co-axial cable</div>
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• Optical fiber</div>
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• Radio waves</div>
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All these mediums differ from each other with respect different parameters. These</div>
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parameters are speed of transmission, range of the receiver and transmitter computer,</div>
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sharing of information, topology, installation & maintenance costs and reliability.</div>
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For example the range of radio waves will be much more than an optical fiber.</div>
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Similarly other mediums differ from each other and appropriate medium is selected</div>
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for the sake of transmission.</div>
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4) BY MOBILITY:</div>
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The networks are also classified according to their mobility.</div>
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In this respect there are two types of networks.</div>
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• Fixed networks</div>
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• Mobile networks</div>
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In these days mobile networks are the hot case. Mobile networks have been emerged</div>
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in the last decade. In this regard there are some issues which are attached with the</div>
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mobility of networks which are as follows:</div>
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• Location and tracking</div>
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• Semi persistent connections</div>
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• Complex administration and billing as devices and users move around the network.</div>
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Satellite/Radio</div>
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Ring</div>
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<div>
NETWORKS IN DAILY LIFE:</div>
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The major use of networks is in business side. Networks are used for advertising,</div>
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production, shipping, planning, billing and accounting purposes. In fact now there is</div>
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an entire industry that develops networking equipment.</div>
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In addition to this networks are being used in homes as well for example, to</div>
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switch and control different devices from one place.</div>
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Networks are very much useful at government level as federal government, local</div>
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government and military organization use networks for communication purposes.</div>
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In education we have online libraries which we can visit at our home PC. This is</div>
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all just due to the networks.</div>
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COMPLEXITY OF NETWORK SYSTEMS:</div>
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A computer network is a complex subject due to the following reasons:</div>
<div>
• MANY DIFFERENT TECHNOLOGIES EXIST:</div>
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The first reason for the complexity of networks is that there are many different</div>
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technologies exist for networking and each technology features is different from the</div>
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other. This is because many companies have developed networking standards, which</div>
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are not compatible with each other. In this way multiple technologies exist that are</div>
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used to connect different networks.</div>
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• NO SINGLE UNDERLYING THEORY OR MODEL:</div>
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The second reason for the complexity of networks is that there is no single underlying</div>
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theory or model, which specifies or defines different aspects of networking. Rather,</div>
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various organizations and research groups have developed conceptual models that can</div>
<div>
be used to explain differences and similarities between network hardware and</div>
<div>
software.</div>
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• MODELS ARE EITHER SO SIMPLISTIC OR SO COMPLEX:</div>
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Another reason for the complexity of networks is that the conceptual models</div>
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made by organization are either so simplistic that they do not distinguish between</div>
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details, or they are so complex that they do not simplify the subject.</div>
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• NO SIMPLE OR UNIFORM TERMINOLOGY:</div>
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One reason for the complexity of networks is that there is no simple or uniform</div>
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terminology that can be used for the same feature. Different technologies use</div>
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different terminologies. In this way terms are confused with product names.</div>
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MASTERING THE COMPLEXITY</div>
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To master the complexity one must follow the following points.</div>
<div>
• CONCENTRATE IN UNDERSTANDING THE CONCEPTS:</div>
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Instead of details of wires used to connect computers to a specific network, it is important</div>
<div>
to understand a few basic categories of wiring schemes their advantages and</div>
<div>
disadvantages.</div>
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For example:</div>
<div>
Instead of how a specific protocol handles congestion, we should concentrate on</div>
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what congestion is and why it must be handled.</div>
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• LEARNING THE NETWORKING TERMINOLOGY:</div>
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The second tool for mastering the complexity is to learn the networking</div>
<div>
terminology. In addition to this one must concentrate the concepts and not details,</div>
<div>
concentrate on breath and not the depth of technologies, also one should understand the</div>
<div>
analogies and illustrations</div>
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Network terminology is introduced with new concepts so it is much helpful to learn the</div>
<div>
terminology to overcome the complexity of networks.</div>
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<div>
Lecture No. 2</div>
<div>
Motivation and Tools</div>
<div>
One of the reasons of motivation towards networking was resource sharing which is</div>
<div>
discussed as follows.</div>
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Resource sharing:</div>
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Resource sharing means to share the resources available among many users.</div>
<div>
In an office as it is very expensive to give a separate printer to each worker. So if the</div>
<div>
printer is shared among the workers then a single printer will be accessible to each</div>
<div>
worker. This leads to the motivation of resource sharing.</div>
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Goal of resource sharing:</div>
<div>
The goal of resource sharing is to make all programs, equipment and date available to</div>
<div>
anyone in the network without regard to physical location of the resource and the</div>
<div>
user.</div>
<div>
For example: the sharing of a printer among the workers in an office and also the</div>
<div>
sharing of information is a goal of resource sharing.</div>
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Main reason for early resource sharing:</div>
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The main reason for early resource sharing was not to share the peripheral devices</div>
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rather to share the large-scale computational power because computer were extremely</div>
<div>
expensive in those days and the government budgets were not sufficient to provide</div>
<div>
computers for all scientist and engineers. By resource sharing a researcher could use</div>
<div>
whichever computer was best suited to perform a given task.</div>
<div>
Efforts of advanced research project AGENCY (ARPA):</div>
<div>
The efforts of ARPA was to enable all its research groups have access to latest</div>
<div>
computers. For this purpose ARPA started investing in ways to do data networking</div>
<div>
ARPA use a new approach consisting of packet switching and internetworking to</div>
<div>
fulfill the purpose of resource sharing. As a result of ARPA research the first network</div>
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was established which was named ARPANET.</div>
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In this way the internet was emerged in 1970’s and it has grown drastically since then</div>
<div>
as shown in the figure below.</div>
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Figure. 2.1 Growth of the Internet</div>
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As shown in another figure below. In log scale the position on y-axis is proportional</div>
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to the log of the number being represented. So the values along y-axis represent the</div>
<div>
power of 10.</div>
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Fig. 2.2 Growth of the internet on Log Scale</div>
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We see that on log scale the growth appears almost linear it means that internet experienced an</div>
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exponential growth. We also observed that internet has been doubled every nine to twelve</div>
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months.</div>
<div>
PROBING THE INTERNET:</div>
<div>
Let us see how are the figures in above graphs obtained?</div>
<div>
In the early days when there were some dozen computers on the network, it was done manually</div>
<div>
but now as we have seen that there are millions of computers on the internet so how can we</div>
<div>
calculate the number of computers connected to the internet. This is done through probing the</div>
<div>
Internet.</div>
<div>
Now an automated tool is required that tests to see whether the given computer is online or not.</div>
<div>
For this purpose the first tool is the `PING program` which is shown in the figure below.</div>
<div>
Figure 2.3 THE PING Command</div>
<div>
We see that 5 packets of 64 bytes are sent to sears.com and 5 packets are received. We see that</div>
<div>
ping has also given some additional information such the IP addresses of sears.com, the sequence</div>
<div>
of packets and the times of transmission known as the round-trip time, as there is no packet loss</div>
<div>
so it means that sears.com is connected to the internet.</div>
<div>
PROBLEM WITH ‘PING’:</div>
<div>
Ping, as a tool seems to be simplistic. Now let’s see what are the problems attached with ping.</div>
<div>
If ping does not review any responses from host computer it can not tell the reason of problem.</div>
<div>
Because one of the following reasons occurs, but ping will not specify the reason.</div>
<div>
• Remote computer might have a problem.</div>
<div>
• Local computer might have a problem.</div>
<div>
• Ping sometimes fails because of congestion.</div>
<div>
Some networks or computers reject the ping packets. They do this to avoid denial of service of</div>
<div>
flooding attack.</div>
<div>
Inspite of these problems ping is still heavily used as a diagnostic tool.</div>
<div>
Network administrators use ping as soon as they learn about the failure.</div>
<div>
Tracing a Route:</div>
<div>
There is another probing tool i-e Trace Route. To get more detail it is used.</div>
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<div>
Figure 2.4</div>
<div>
As shown in the figure about the route to DANDELION-PATCH.MIT.EDU was traced out and</div>
<div>
the program showed all eight computers that were in the way. The additional information is also</div>
<div>
shown in the figure.</div>
<div>
Thus we see that tracing a route is more interesting tool than Ping as it tells about each computer</div>
<div>
that falls in the way of source and destination computers.</div>
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<div>
Lecture No. 3</div>
<div>
Overview of Data Communication</div>
<div>
NOTE: -</div>
<div>
Chapter 4, 5, 6 deals with the course of DATA COMMUNICATION, which has</div>
<div>
been studied as a separate, course earlier. So these chapters are just overviewed and can</div>
<div>
be seen in the third lecture video.</div>
<div>
It should also be noted that these chapters will contain no assignment, or quizzes</div>
<div>
and these chapters will also be out of the examination.</div>
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<div>
Lecture No. 4</div>
<div>
PACKETS, FRAMES AND ERROR DETECTION</div>
<div>
INTRODUCTION:</div>
<div>
The previous chapters of data communication described how bits are transmitted</div>
<div>
across a physical network using a transmission medium.</div>
<div>
This chapter introduces the concept of packets of data rather than bits for</div>
<div>
communication.</div>
<div>
CONCEPT OF ‘PACKET’:</div>
<div>
Network systems divide data in small blocks or junks called packets, which they</div>
<div>
send individually. Why we need packets rather than bits? The answer to this question is</div>
<div>
because a sender and receiver need to coordinate to detect transmission errors. Also the</div>
<div>
individual connection between each pair of computers is not possible. That’s why to</div>
<div>
solve these problems shard network connections are made among many workstations.</div>
<div>
PROBLEMS WITH SHARING:</div>
<div>
The demand of sharing is very high because many computers need to use the shared</div>
<div>
networks. In addition to this some applications have large data transfer. In this way they</div>
<div>
hold the network for long time. But on the other hand some applications cannot wait so</div>
<div>
long. So we need a mechanism for fairness.</div>
<div>
SOLUTION FOR FAIRNESS:</div>
<div>
To the fairness, the solution is to divide the data into small block or chunks called</div>
<div>
‘PACKETS’. Computers take turns to send one packet at a time over the shared</div>
<div>
connection.</div>
<div>
Because each packet is small so no computer experiences a long delay.</div>
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Example:</div>
<div>
In the figure one reason for using the packets is illustrated. We see that in a shared</div>
<div>
resource when one pair of computer communicates, the other must wait. To understand</div>
<div>
the use of packet here, let’s suppose a transmission with packets in the figure.</div>
<div>
WITHOUT PACKETS:</div>
<div>
A 5MB file transferred across network with 56Kpbs capacity will require 12 minutes.</div>
<div>
This means that all that computers will be forced to wait for 12 minutes before initiating</div>
<div>
other transfers.</div>
<div>
WITH PACKETS:</div>
<div>
Now if the file is broken into packets, other computers must only wait until packet (not</div>
<div>
entire file) has been sent.</div>
<div>
Suppose file is broken into 1000 byte packets.</div>
<div>
Now each packet takes less than 0.2 seconds to transmit. Here other computers must only</div>
<div>
wait for 0.14 sec before beginning to transmit.</div>
<div>
Note: - if both files are 5MB long, each now takes 24 minutes to transmit. But if the</div>
<div>
second file is 10MB long it sill be transmitted in only 2.8 seconds while 5MB file still</div>
<div>
takes roughly 12 minutes.</div>
<div>
PACKETS AND TDM:</div>
<div>
Dividing data into small packets allow time division multiplexing. In TDM each packet</div>
<div>
leaves the source and is switched on the shared communication channel through a</div>
<div>
multiplexer. At the destination the packet is switched through a demultiplexer to the</div>
<div>
destination.</div>
<div>
In the figure this process is illustrated with a multiplexing circuit shown.</div>
<div>
5x10 bytes * 8 bits / byte</div>
<div>
60 secs / minute * 56x10 bits / second</div>
<div>
11.9 minutes</div>
<div>
6</div>
<div>
3 =</div>
<div>
1000 bytes * 8 bits / byte</div>
<div>
56x10 bits / second</div>
<div>
.143 seconds 3 =</div>
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COMPUTER NETWORKS (CS610) VU</div>
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<div>
Figure 4.2 illustration of TDM</div>
<div>
PACKETS AND FRAMES:</div>
<div>
PACKETS:</div>
<div>
Packet is a generic term that refers to small block of data. Packet have different</div>
<div>
format. Each hardware uses different packet format.</div>
<div>
FRAME:</div>
<div>
A frame or hardware frame denotes a packet of a specific format on a specific</div>
<div>
hardware technology.</div>
<div>
FRAME FORMAT:</div>
<div>
We need to define a standard format for data to indicate the beginning and end of</div>
<div>
the frame. Header and tail are used to frame the data as shown in the figure below.</div>
<div>
Figure 4.3 illustration of a Frame</div>
<div>
We see that in the figure soh and eot are used to denote the start of header and end of tail.</div>
<div>
FRAMING IN PRACTICE:</div>
<div>
In practice there is a disadvantage of overhead. To avoid the no delay between</div>
<div>
two frames each frame sends an extra character between block of data.</div>
<div>
The framing in practice also has some transmission problems just like:</div>
<div>
• Missing eot indicates sending computer crashed.</div>
<div>
• Missing soh indicates receiving computer missed beginning of message.</div>
<div>
• Bad frame is discarded.</div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Lecture No. 5</div>
<div>
BYTE STUFFING</div>
<div>
Sometimes the special character (i-e soh and eot) may appear in data and as a part of data</div>
<div>
they will be misinterpreted as framing data.</div>
<div>
The solution to this problem is Byte stuffing.</div>
<div>
In general to distinguish between data being sent and control information such as</div>
<div>
frame delimiters network systems arrange for the sending side to change the data slightly</div>
<div>
before it is sent because systems usually insert data or bytes to change data for</div>
<div>
transmission, the technique is known as Data Stuffing.</div>
<div>
There are two types of data stuffing:</div>
<div>
• Byte Stuffing</div>
<div>
• Bit Stuffing</div>
<div>
Byte stuffing refers stuffing with character oriented hardware and bit stuffing</div>
<div>
refers to bit oriented hardware.</div>
<div>
Byte stuffing translates each reserved byte into two unreserved bytes. For</div>
<div>
example: it can use esc as prefix followed by x for soh, y for eot and z for eco.</div>
<div>
The receiver then replaces each occurrence of esc x, esc y and esc z by the</div>
<div>
corresponding single character. This is shown in figure below:</div>
<div>
Figure 5.1</div>
<div>
Byte stuffing is illustrated in another figure below we can see the replacement of</div>
<div>
characters.</div>
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<div>
TRANSMISSION ERRORS:</div>
<div>
Transmission errors may occur due to different causes for example interference or</div>
<div>
power surges may destroy data during transmission. In result of which the bits are lost or</div>
<div>
the bit value may be changed.</div>
<div>
ERROR DETECTION AND CORRECTION:</div>
<div>
To detect and correct errors, frames include additional information, which is</div>
<div>
inserted by the sender and checked by the receiver. In this way incorrect data can be</div>
<div>
rejected. Also the incorrect data can be corrected and accepted.</div>
<div>
PARITY CHECKING:</div>
<div>
To detect the error there are different schemes in which parity checking is also</div>
<div>
commonly used. In parity checking, parity refers to the number of bits set to 1 in the data</div>
<div>
item.</div>
<div>
There are two types:</div>
<div>
• Even Parity</div>
<div>
• Odd Parity</div>
<div>
EVEN PARITY:</div>
<div>
In an even parity the no. of 1’s in data should be an even number.</div>
<div>
ODD PARITY:</div>
<div>
In an Odd parity the no. of bits should be an odd number.</div>
<div>
PARITY BIT:</div>
<div>
A parity bit is an extra bit transmitted with data item chose to give the resulting bit even</div>
<div>
or odd parity.</div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
For example an even parity data 10010001 has parity bit 1 as it has odd number of 1’s.</div>
<div>
An odd parity data 10010111 has parity bit 0 as it has odd number of 1’s.</div>
<div>
Let us consider another example, if noise or other interference introduces an error</div>
<div>
one of the bits in the data will be changed from a 1 to a 0 or from a 0 to a 1. Thus the</div>
<div>
parity of resulting bits will be large.</div>
<div>
Suppose original data and parity is 10010001+1 (even parity). After interference the</div>
<div>
incorrect data is 10110001+1 and it has become an odd parity.</div>
<div>
LIMITATIONS OF PARITY CHECKING:</div>
<div>
Parity can only detect errors that change in odd number of bits for example the original</div>
<div>
data and parity is 10010001+1 (even parity) and the incorrect data is 10110011+1 (even</div>
<div>
parity). We see that even no. of bits have been changed due to noise so parity checking</div>
<div>
can not detect this error.</div>
<div>
Parity usually is used to detect on bit error.</div>
<div>
ALTERNATIVE ERROR DETECTION SCHEMES:</div>
<div>
In addition to parity checking alternative error detection mechanisms have been</div>
<div>
introduced. These mechanisms differ from each other by the following respects.</div>
<div>
• The size of the additional information (transmission overhead)</div>
<div>
• Computational complexity of the algorithm (computational overhead)</div>
<div>
• The number of bits errors that can be detected (how well errors are detected )</div>
<div>
CHECKSUM</div>
<div>
The second procedure used to detect errors is checksum. In this procedure data is</div>
<div>
treated as a sequence of integers and their arithmetic sum is computed and the carry bits</div>
<div>
are added to the final sum. Then checksum is calculated by transmission then it is sent</div>
<div>
along the data and the receiver and the same calculation is performed and then compared</div>
<div>
with the original checksum transmitted. In this way errors are detected if the received</div>
<div>
checksum is different from the sent.</div>
<div>
The figure illustrates the example.</div>
<div>
Figure 5.3</div>
<div>
The integers can be 8, 16 or 32 bits. Checksum is easy to do. It uses only addition but it</div>
<div>
has also limitations and can not detect all errors. As shown below.</div>
<div>
COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Figure 5.4</div>
<div>
CYCLIC REDUNDANCY CHECK (CRC):</div>
<div>
To enable a network system to detect move error without increasing the amount</div>
<div>
of information in each packet another most successful approach is made which is called</div>
<div>
CRC.</div>
<div>
To understand the concepts of CRC consider data in a message as co-efficient of a</div>
<div>
polynomial. Their co-efficient set is divided by a known polynomial.</div>
<div>
The remainder of this division is then transmitted as CRC and checked at the</div>
<div>
receiver to detect errors.</div>
<div>
CRC has good error detection properties. It is easy to implement in hardware.</div>
<div>
HARDWARE COMPONENTS USED IN CRC:</div>
<div>
CRC uses just two hardware components:</div>
<div>
• Shift register</div>
<div>
• Exclusive OR ( XOR unit )</div>
<div>
The XOR unit is shown in the figure below.</div>
<div>
Figure 5.5</div>
<div>
Shift register is also shown in figure. It performs two operations.</div>
<div>
• Initialize: sets all bits to zero</div>
<div>
• Shift: moves all bits to the left position.</div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Figure 5.6</div>
<div>
COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Lecture No. 6</div>
<div>
SHIFT OPERATION</div>
<div>
This operation shifts all bits to the left one position. For example in the figure</div>
<div>
below a 16-bit CRC hardware is shown, which uses three shift registers and three</div>
<div>
Exclusive OR (XOR) units.</div>
<div>
Figure 6.1</div>
<div>
We see that this hardware can compute 16-bit CRC. Also in the figure, we see that the</div>
<div>
registers are initialized to zero and the bits of message are shifted through the input.</div>
<div>
When all 16 bits are shifted then the CRC is found in the registers.</div>
<div>
In another figure, we see that input data is all 1s and CRC shown after 15, 16, 17</div>
<div>
bits are shifted and feedback introduces 0s in CRC.</div>
<div>
TYPES OF ERRORS:</div>
<div>
CRC can check the following errors better than check sums.</div>
<div>
a) Vertical errors b) Burst errors</div>
<div>
a) VERTICAL ERRORS:</div>
<div>
This type of error occurs due to a hardware failure. e.g. the second bit of every</div>
<div>
character will damage.</div>
<div>
b) BURST ERRORS:</div>
<div>
When a small set of bits changes near a specific location due to lighting or electric motor</div>
<div>
starting nearby etc. then these types of errors are called Burst errors.</div>
<div>
FRAME FORMAT AND ERROR DETECTION:</div>
<div>
The modified frame format also includes CRC. If there is an error occurred in</div>
<div>
frame, then it typically causes receiver to discard frame. The frame including CRC is</div>
<div>
shown in the figure.</div>
<div>
Figure 6.2</div>
<div>
COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
LAN TECHNOLOGY AND NETWORK TOPOLOGY</div>
<div>
Most networks are local and are designed to share resources among multiple</div>
<div>
computers. Hardware technologies used for local networks allow multiple devices to</div>
<div>
connect with a shared network. In this shared medium the computers must take turns</div>
<div>
using the shared medium.</div>
<div>
DIRECT POINT-TO-POINT COMMUNICATION:</div>
<div>
Early networks used direct point-to-point communication. In such a mode of</div>
<div>
communication each communication channel connects exactly two computers. In this</div>
<div>
way it forms a mesh or point-to-point network, which is shown in the figure below.</div>
<div>
Figure 6.3</div>
<div>
ADVANTAGES:</div>
<div>
Direct point-to-point communication has the following advantages:</div>
<div>
• The connection type of individual connections can be different.</div>
<div>
• Individual connections can choose a different frame format and error detection</div>
<div>
mechanism etc.</div>
<div>
• It is easy to enforce security and privacy.</div>
<div>
DISADVANTAGES:</div>
<div>
Direct point-to-point communication has the following disadvantages:</div>
<div>
• The no. of connections grow more rapidly than the no. of computers</div>
<div>
• For ‘n’ computers connections = (n^2 – n)/2.</div>
<div>
• Most computers use the same physical path.</div>
<div>
• Direct point-to-point communication is expensive due to a no. of connections.</div>
<div>
• Another disadvantage is that adding a new computer to the network requires N-1 new</div>
<div>
connections as shown in the above figure.</div>
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COMPUTER NETWORKS (CS610) VU</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Lecture No. 7</div>
<div>
GROWTH OF LAN TECHNOLOGY</div>
<div>
The development of shared communication channels (LANs) started in 1960s and</div>
<div>
early 1970.</div>
<div>
The key idea behind was to reduce the number of connections by sharing connection</div>
<div>
among many computers</div>
<div>
Each LAN consists of a single shared medium. The computers take turns using</div>
<div>
the medium. First one computer uses the medium to send its data over the channel then</div>
<div>
second and son on. But sharing a single medium over long distances is efficient, due to</div>
<div>
the long delays.</div>
<div>
LAN technologies reduce cost by reducing no. of connections. But attached</div>
<div>
computers compete for use of shared connections. The local communication consists of</div>
<div>
LAN exclusively. But the long distance communication is point-to-point exclusively.</div>
<div>
SIGNIFICATION OF LANs AND LOCALITY OF REFERENCE:</div>
<div>
LANs are most popular form of computer networks. One of its bright features is</div>
<div>
that this technology is inexpensive. The demand of LANs is related to a principle known</div>
<div>
as “Locality of Reference Principle”.</div>
<div>
“LOCALITY OF REFERENCE” PRINCIPLE:</div>
<div>
Principle of “Locality of Reference” helps predict computer communication</div>
<div>
patterns. There are two patterns given as follows:</div>
<div>
A) SPATIAL LOCALITY OF REFERENCE</div>
<div>
B) TEMPORAL LOCALITY OF REFERENCE</div>
<div>
a) SPATIAL LOCALITY OF REFERENCE:</div>
<div>
In this pattern computers are likely to communicate with other computers that are located</div>
<div>
nearby.</div>
<div>
b) TEMPORAL LOCALITY OF REFERENCE:</div>
<div>
In this pattern computers are likely to communicate with the same computers repeatedly.</div>
<div>
Thus LANs are effective because of spatial locality of reference. Temporal locality of</div>
<div>
reference may give insight into which computers should be on a LAN.</div>
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© Copyright Virtual University of Pakistan</div>
<div>
LAN TOPOLOGIES:</div>
<div>
Network can be classified by shape. According to which there are three most</div>
<div>
popular topologies, which are given as follows;</div>
<div>
• Star</div>
<div>
• Ring</div>
<div>
• Bus</div>
<div>
STAR TOPOLOGY:</div>
<div>
In this topology, all computers are attached to a central point, which is sometimes</div>
<div>
called the “Hub” as shown in the figure below.</div>
<div>
FIGURE 7.1 AN IDEALIZED STAR NETWORK</div>
<div>
It is important to note that these networks are not physically like stars but they are</div>
<div>
logically like stars. It means that their shape does not look like a star but their</div>
<div>
connections are just like a star. The above diagram is idealized. Here is shown a star</div>
<div>
network in practice in the figure below:</div>
<div>
FIGURE 7.2 STAR NETWORK IN PRACTICE</div>
<div>
RING TOPOLOGY:</div>
<div>
In this topology of network the computers are connected to each other in closed</div>
<div>
loop. In this network first computer passes data to the second and then second passes data</div>
<div>
to third and so on, as shown in the figure.</div>
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<div>
FIGURE 7.3</div>
<div>
Like star topology the ring network are also logically ring and not physically.</div>
<div>
BUS TOPOLOGY:</div>
<div>
In a bus topology all computers are attached to a single long cable and any</div>
<div>
computer can send data to any other computer.</div>
<div>
For this purpose, coordination is required to decide which computer has to use the</div>
<div>
line at what time. The bus topology is shown below:</div>
<div>
FIGURE 7.4 BUS TOPOLOGY</div>
<div>
REASON FOR MULTIPLE TOPOLOGIES:</div>
<div>
Each topology has advantages and disadvantages, which are discussed below:</div>
<div>
IN A RING:</div>
<div>
It is easy to coordinate access to other computers however entire network is</div>
<div>
disabled if a cable cut occurs.</div>
<div>
IN A STAR:</div>
<div>
On the other hand only once computer is affected when a cable cut occurs.</div>
<div>
IN A BUS:</div>
<div>
The network needs fewer wires than a star, however entire network is disabled</div>
<div>
when a cable cut occurs.</div>
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© Copyright Virtual University of Pakistan</div>
<div>
EXAMPLE BUS NETWORK; ETHERNET:</div>
<div>
Ethernet is a widely used LAN technology. It was invented at EXROX PARC</div>
<div>
(Palo Alto Research Center) in 1970s.</div>
<div>
Xerox, Intel and Digital defined it in a standard so it is also called DIX standard. The</div>
<div>
standard is now managed by IEEE in which 802.3 standard of IEEE defines formats,</div>
<div>
voltages of cable length etc.</div>
<div>
The Ethernet uses bus topology. It uses a single coaxial cable. To which multiple</div>
<div>
computers connect.</div>
<div>
One Ethernet cable is sometimes called a segment. This segment is limited to 500</div>
<div>
meters in length. The minimum separation between connections is 3 meters.</div>
<div>
ETHERNET SPEEDS:</div>
<div>
The Ethernet speed was originally 3Mbps, and the current standard is 10Mbps</div>
<div>
the fast Ethernet operates at 100Mbps. There are also gigabits Ethernet available now.</div>
<div>
ENCODING USED IN ETHERNET:</div>
<div>
The encoding used in Ethernet is Manchester encoding. It uses signal changes to</div>
<div>
encode data.</div>
<div>
e.g. A change from positive voltage to 0 encodes as shown in the figure below:</div>
<div>
FIGURE 7.5</div>
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© Copyright Virtual University of Pakistan</div>
<div>
Lecture No. 8</div>
<div>
CARRIER SENSE MULTIPLE ACCESS (CSMA)</div>
<div>
There is no central control management when computers transmit on Ethernet.</div>
<div>
For this purpose the Ethernet employs CSMA to coordinate transmission among multiple</div>
<div>
attached computers.</div>
<div>
CSMA is a coordination scheme that defines how to take turns using a shared</div>
<div>
cable.</div>
<div>
A computer listen to the codes i.e. it senses the carrier. If the cable is idle it starts</div>
<div>
transmitting and if the cable is in use then it waits.</div>
<div>
If simultaneous transmission occurs, the frames interfere with each other and this</div>
<div>
phenomenon is called collision.</div>
<div>
COLLISION DETECTION:</div>
<div>
As explained above, the signals from two computers will interfere with each other</div>
<div>
and the overlapping of frames is called a collision.</div>
<div>
It does not harm to the hardware but data from both frames is grabbled.</div>
<div>
ETHERNET CD:</div>
<div>
To detect the collision, Ethernet interfaces include hardware to detect</div>
<div>
transmission. It performs two operations:</div>
<div>
• It monitors outgoing signals.</div>
<div>
• Grabbled signal is interpreted as a collision.</div>
<div>
After collision is detected computers stop transmitting. So Ethernet uses CSMA/CD to</div>
<div>
coordinate transmission.</div>
<div>
RECOVERY FROM COLLISION:</div>
<div>
Computer that detects a collision sends special signal to force all other interfaces</div>
<div>
to detect collision.</div>
<div>
Computer then waits for other to be idle before transmission. But if both</div>
<div>
computers wait for same length of time, frames will collide again. So the standard</div>
<div>
specifies maximum delay and both computers choose random delay, which is lesser.</div>
<div>
After waiting, computers use carrier sense to avoid subsequence collision.</div>
<div>
The computer with shorter delay will go first and other computer may transmit later.</div>
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<div>
EXPONENTIAL BACK OFF:</div>
<div>
Even with random delays, collision may occur especially likely with busy</div>
<div>
segments. Computers double delay with each subsequent collision. It reduces likely hood</div>
<div>
of sequence of collision.</div>
<div>
802.11 WIRELESS LANs AND CSMA/CA:</div>
<div>
IEEE 802.11 is standard wireless LAN that uses radio signals at 2.4GHz. Its data</div>
<div>
rate is 11Mbps. The older devices use radio signals at 900MHz and data rate of 2Mbps.</div>
<div>
Bluetooth specifies a wireless LAN for short distances. It uses shared medium and radio</div>
<div>
waves instead of coaxial cable.</div>
<div>
LIMITED CONNECTIVITY WITH WIRELESS:</div>
<div>
In contrast with wired LANs, not all participants may be able to reach each other.</div>
<div>
Because:</div>
<div>
• It has low signal strength.</div>
<div>
• In wireless LANs the propagation is blocked by walls etc.</div>
<div>
• It can’t depend on CD to avoid interference because not all participants may hear.</div>
<div>
This is shown in the figure below:</div>
<div>
FIGURE 8.1</div>
<div>
CSMA/CA:</div>
<div>
Wireless uses collision avoid ness rather than collision detection. Transmitting</div>
<div>
computer sends very short message to receiver. Receiver responds with short message</div>
<div>
reserving slot for transmitter. The response from receiver is broadcast, so all potential</div>
<div>
transmitters receive reservation.</div>
<div>
COLLISION:</div>
<div>
The receiver may receive simultaneous requests, which results in collision at</div>
<div>
receivers and both requests lost and in this way no transmitter receives reservations and</div>
<div>
both use back off and retry. The receiver may receive closely spaced requests. It selects</div>
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<div>
one of them and then the selected transmitter sends message and the transmitter not</div>
<div>
selected uses back off and retries.</div>
<div>
LOCAL TALK:</div>
<div>
Apple invented the LAN technology that uses bus topology. Its interface is</div>
<div>
included with all Macintosh computers.</div>
<div>
It has relatively low speed i.e. 230.4Kbps. Also it is of low cost and we can get a free</div>
<div>
with a Macintosh, which is easy to install and connect. It uses CSMA/CA.</div>
<div>
TOKEN RING:</div>
<div>
Many LAN technologies that are ring topology use token passing for</div>
<div>
synchronized access to the ring. The ring itself is treated as a single shared</div>
<div>
communication medium. Both pass from transmitter passed by other computers and are</div>
<div>
copied by destination.</div>
<div>
Hardware must be designed to pass token ever if attached computer powered</div>
<div>
down. This is shown in figure below.</div>
<div>
FIGURE 8.2</div>
<div>
USING THE TOKEN:</div>
<div>
When a computer waits to transmit it waits a token. After transmission computer</div>
<div>
transmits token on ring. Next computer is then ready to transmit, receive and then</div>
<div>
transmits.</div>
<div>
TOKEN AND SYNCHRONIZATION:</div>
<div>
Because there is only one token, only one computer will transmit at a time.</div>
<div>
Token is a short reserved frame that can not appear in data.</div>
<div>
Hardware must regenerate token if lost. Token gives computer permission to send</div>
<div>
one frame. If all computers are ready to transmit it enforces Round-Robin access. But if</div>
<div>
now computer is ready to transmit, token circulates around ring.</div>
<div>
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<div>
IBM TOKEN RING:</div>
<div>
It is very widely used. It was originally 4Mbps and now it is upto 16Mbps. It uses</div>
<div>
special connection cable between the computer and the Ring interface.</div>
<div>
FDDI: Fiber distributed data interconnect (FDDI) is another ring technology. Its most</div>
<div>
important features are:</div>
<div>
It uses fiber optics between stations and transmits data at 100Mbps.</div>
<div>
It uses pair of fibers to form two concentric rings.</div>
<div>
FDDI AND RELIABILITY:</div>
<div>
FDDI uses counter rotating rings in which data flows in opposite directions.</div>
<div>
In case of fiber a station failure, remaining stations loop back and reroute data through</div>
<div>
spare ring. In this way all stations automatically configure loop back by monitoring data</div>
<div>
ring. It is shown in figure below</div>
<div>
FIGURE 8.3 FDDI AND RELIABILITY:</div>
<div>
ATM ----STAR NETWORK:</div>
<div>
The ATM (Asynchronous Transferred Mode) technology consists of electronic</div>
<div>
packet switches to which the computers can connect.</div>
<div>
ATM switches form a hub into which computers can connect in a star topology.</div>
<div>
Computer gets point-to-point connections. Data from transmitters is routed directly</div>
<div>
through hub switches to destination. An ATM star network is shown in the figure below:</div>
<div>
FIGURE 8.4 ATM SWITCH</div>
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<div>
ATM DETAILS:</div>
<div>
• It transmits data at over 100Mbps.</div>
<div>
• It uses fiber optics to connect computer to switch.</div>
<div>
• Each connection includes two fibers.</div>
<div>
• It is also shown in figure.</div>
<div>
FIGURE 8.5</div>
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<div>
Lecture No. 9</div>
<div>
HARDWARE ADDRESSING</div>
<div>
We need to devise technique for delivering message through LAN medium to</div>
<div>
single, specific destination computer. Sending computer uses a hardware address to</div>
<div>
identify the intended destination of a frame. The sending computer also identifies type of</div>
<div>
data carried in the frame.</div>
<div>
SPECIFYING A DESTINATION:</div>
<div>
The data sent across a shared network reaches all attached stations - for all LAN</div>
<div>
topologies. Interface hardware detects delivery of frame and extracts frame from</div>
<div>
medium. But most applications want data to be delivered to one specific application on</div>
<div>
another computer but not all computers.</div>
<div>
HARDWARE ADDRESSING:</div>
<div>
Most network technologies have a hardware-addressing scheme that identifies stations on</div>
<div>
the network. Each station is assigned a numeric hardware address or physical address. .</div>
<div>
Sender also includes hardware address in each transmitted frame. In this way only station</div>
<div>
identified in frame receives copy of frame. Most LAN technologies include sender's</div>
<div>
hardware address in frame too.</div>
<div>
LAN HARDWARE AND PACKET FILTERING:</div>
<div>
The figure below illustrates the LAN hardware:</div>
<div>
Figure 9.1</div>
<div>
LAN INTERFACE:</div>
<div>
LAN interface handles all details of frame transmission and reception which are</div>
<div>
given as follows:</div>
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<div>
• It adds hardware addresses, error detection codes, etc. to outgoing frames.</div>
<div>
• It may use DMA to copy frame data directly from main memory.</div>
<div>
• It obeys access rules (e.g., CSMA/CD) when transmitting.</div>
<div>
• It checks error detection codes on incoming frames.</div>
<div>
• It may use DMA to copy data directly into main memory.</div>
<div>
• It checks destination address on incoming frames.</div>
<div>
• The frames not addressed to the local computer are ignored and don't affect</div>
<div>
the local computer in any way.</div>
<div>
FORMAT OF HARDWARE ADDRESS:</div>
<div>
It consists of a numeric value and its size is selected for specific network</div>
<div>
technology. The length of the format is one to six bytes.</div>
<div>
ASSINGING HARDWARE ADDRESS:</div>
<div>
The hardware address must be unique on a LAN. How can those addresses be</div>
<div>
assigned and who is responsible for uniqueness? The answer to these questions depends</div>
<div>
on the particular LAN technology being used. There are three categories of address</div>
<div>
forms:</div>
<div>
• Static</div>
<div>
• Configurable</div>
<div>
• Dynamic</div>
<div>
STATIC:</div>
<div>
In this category the hardware manufacturer assigns permanent physical address to</div>
<div>
each network interface and manufacturer must ensure that every interface has a unique</div>
<div>
address.</div>
<div>
CONFIGURABLE:</div>
<div>
In this category, the address can be set by the end user either manually e.g.</div>
<div>
switches or jumpers on the interface or electronically (e.g. through software).</div>
<div>
The system administrators must coordinate to avoid the conflict.</div>
<div>
DYNAMIC:</div>
<div>
In this category the interface automatically assigns physical address each time it is</div>
<div>
powered up. This automatic scheme must be reliable to prevent conflicts.</div>
<div>
BROADCASTING:</div>
<div>
Some applications want to broadcast messages to all stations on the LAN. For this</div>
<div>
purpose shared communication channel can make broadcast efficient in such a way that</div>
<div>
message is delivered to all stations. A special broadcast address is used to identify</div>
<div>
broadcast message, which are captured by all stations.</div>
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<div>
Lecture No. 10</div>
<div>
FRAME TYPE IDENTIFICATION</div>
<div>
There are some problems with the broadcast. For every broadcast frame on the</div>
<div>
network each computer uses computational resources and places the contents into</div>
<div>
memory, which interrupt the CPU. It allows system software to make the decision</div>
<div>
whether to discard or use the frames.</div>
<div>
Another problem is that if a pair of computer use broadcasting instead of sending</div>
<div>
them directly all other computers waste CPU time while discarding the frames.</div>
<div>
MULTICASTING:</div>
<div>
The solution to above problem is multicasting. It is the restricted form of</div>
<div>
broadcasting. It works like broadcasting however it does not forward frames</div>
<div>
automatically to the CPU.</div>
<div>
The interface hardware is programmed in advance to accept certain frames that have</div>
<div>
multicast address as the destination address.</div>
<div>
If an application program wishes to receive certain frames then it program the interface</div>
<div>
hardware to accept an additional set of addresses.</div>
<div>
The interface hardware frame then begins accepting three types of frames:</div>
<div>
• Multicast frames</div>
<div>
• Broadcast frames</div>
<div>
• The frames that are distend to the station itself.</div>
<div>
MULTICAST ADDRESSING:</div>
<div>
We take an example of computers running an audio application. We see that they</div>
<div>
can receive audio frames if the interface are programmed to received them and the other</div>
<div>
computers that are not running that audio application will not waste resources</div>
<div>
.</div>
<div>
IDENTIFYING PACKET CONTENTS:</div>
<div>
The destination must get some clue about how to interpret frame data. For this</div>
<div>
purpose it can use two types which are given as follows.</div>
<div>
EXPLICIT FRAME TYPE:</div>
<div>
In this type the identifying value is included with frame describes types of</div>
<div>
included data.</div>
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<div>
IMPLICIT FRAME TYPE:</div>
<div>
In implicit frame the receiver must infer from frame data.</div>
<div>
HEADERS AND FRAME FORMAT:</div>
<div>
LAN technology standards define frame format for each technology. All</div>
<div>
contemporary standards use the following general format.</div>
<div>
a) Frame header b) payload</div>
<div>
Frame header has address and other identifying information.</div>
<div>
Information typically in fields has fixed size and location. The data area may vary in size.</div>
<div>
The Ethernet frame format is shown in the figure.</div>
<div>
Figure 10.1 the Ethernet frame format</div>
<div>
The different friends of ether frame format and their purposes is explained below:</div>
<div>
FIELD PURPOSE</div>
<div>
Preamble Receiver synchronization</div>
<div>
Destination Address Identifies intended receiver</div>
<div>
Source Address Hardware address of sender</div>
<div>
Frame Type Type of data carried in frame</div>
<div>
Data Frame payload</div>
<div>
CRC 32-bit CRC code</div>
<div>
ETHERNET FIELDS:</div>
<div>
In Ethernet fields the preamble and CRC is often not shown in frame. The</div>
<div>
destination address of all is the broadcast address. There is special value reserved for</div>
<div>
frame type field.</div>
<div>
FRAME WITHOUT TYPE FIELDS:</div>
<div>
Some LAN technologies do not include a type field.</div>
<div>
Sender and receiver can agree on interpretation, which is as follows:</div>
<div>
They agree on single data format and use only that format this limits to one type of data.</div>
<div>
In this way all computers on LAN must use one format. Also they agree to encode the</div>
<div>
data format into first few bytes of the data field.</div>
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<div>
ENCODING THE DATA TYPE:</div>
<div>
The figure illustrates a frame in which the data type is specified by using the data area.</div>
<div>
Figure 10.2. Encoding the data type</div>
<div>
To ensure interoperability format of encoding area must be universally agreed upon it</div>
<div>
typically set by standards only.</div>
<div>
IEEE 802.2 LLC:</div>
<div>
IEEE 802.2 standard includes logical link control (LLC) sub network attachment</div>
<div>
point (SNAP) header. SNAP/LLC format is widely used for example by Ethernet.</div>
<div>
This is shown in figure below:</div>
<div>
Figure 10.3. SNAP/LLC format</div>
<div>
In the figure LLC portion indicates SNAP field to follow OUI (organizationally unique</div>
<div>
identifier) identifies Ethernet specification organization.</div>
<div>
Also the type field is interpreted as in Ethernet (in this case, IP ) as shown in</div>
<div>
figure above.</div>
<div>
UNKNOWN TYPES:</div>
<div>
For either encoding format some computer may not be prepared to accept frames</div>
<div>
of some types, which are unknown e.g. protocol type is not installed and the newly</div>
<div>
defined type.</div>
<div>
The receiving computer examines the field and discards any frame with unknown type.</div>
<div>
NETWORK ANALYZERS:</div>
<div>
A network analyzer also called network monitor or a network sniffer is used to examine</div>
<div>
the performance of or debug a network.</div>
<div>
It can report statistics such as capacity utilization, distribution of frame size,</div>
<div>
collision rate or token circulation time.</div>
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<div>
OPERATION OF NETWORK ANALYZERS:</div>
<div>
The basic idea behind the operation of network analyzer is a computer with a</div>
<div>
network interface that receives all frames, which is called promiscuous mode.</div>
<div>
Many desktop computers have interface that can be configured for promiscuous mode.</div>
<div>
When combined with software computer can examine any frame on LAN. In this way the</div>
<div>
communication across LAN is guaranteed to be private. This computer receives and</div>
<div>
displays (but does not respond to) frames on the LAN.</div>
<div>
Network analyzer can be configured to filter and process frames. It can count</div>
<div>
frames of specific type of size.</div>
<div>
It displays only frames from or to specific computers. In general it can be configured to</div>
<div>
match any value of any field and capture only these frames meeting the filter</div>
<div>
specifications.</div>
<div>
`</div>
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<div>
Lecture No. 11</div>
<div>
INTERFACE HARDWARE</div>
<div>
LAN data transmission speeds are typically fast relative to CPU speeds. LANs</div>
<div>
speeds are defined independent of any specific processor speeds, which allows for mix of</div>
<div>
any attached systems. In this way new computers can be attached without affecting LAN</div>
<div>
speeds.</div>
<div>
NETWORK INTERFACE HARDWARE:</div>
<div>
CPU can’t process data at network speeds. So in order to connect to the network</div>
<div>
computer systems use special purpose hardware for network connections which consists</div>
<div>
of typically a separate card in the back plane which is called Network Adapter Card or</div>
<div>
Network Interface Card (NIC).</div>
<div>
The connector on NIC at the back of computer then accepts cable to physical</div>
<div>
network. The CPU structure is shown in the figure.</div>
<div>
Figure 11.1</div>
<div>
The Network Connector is also shown in the figure below.</div>
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<div>
Figure 11.2</div>
<div>
NICs AND NETWORK HARDWARE:</div>
<div>
NIC is built for one kind of physical network. For example Ethernet interface can</div>
<div>
not be used with token ring and similarly ATM interface cannot be used with FDDI.</div>
<div>
Some NICs can be used with different but similar hardware for example thick,</div>
<div>
thin and 10 Base-T Ethernet, 10Mbps and 100Mbps Ethernet.</div>
<div>
NIC AND CPU PRCESSING:</div>
<div>
NIC contains sufficient hardware to process data independent of system CPU. In</div>
<div>
which some NICs contain separate microprocessor. In addition to this it also include</div>
<div>
analog circuitry interface to system bus, buffering and processing.</div>
<div>
NIC looks like any other I/O device to system CPU. The system CPU forms</div>
<div>
message request and sends instructions to NIC to transmit data. NIC also receives</div>
<div>
interrupt on incoming data.</div>
<div>
CONNECTION BETWEEN NIC AND PHYSICAL</div>
<div>
NETWORK:</div>
<div>
TWO ALTERNATIVES:</div>
<div>
NIC contains all circuitry and connects directly to network medium. A cable from NIC</div>
<div>
connects to additional circuitry that then attaches to the network medium.</div>
<div>
THIN ETHERNET VERSUS 10BASE-T:</div>
<div>
Thin Ethernet and 10Base-T are both Ethernet. The network technology is not</div>
<div>
limited to one style of connection.</div>
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<div>
THICK ETHERNET WIRING:</div>
<div>
It uses thick coax cable. AUI cable (or transceiver or drop cable) connects from</div>
<div>
NIC to transceiver. AUI cable carries digital signal from NIC to transceiver. The</div>
<div>
transceiver generates analog signal on coax cable. The wires in AUI carry digital signals</div>
<div>
power and other control signals. Thick Ethernet also requires terminators to avoid signal</div>
<div>
reflectance. This is shown in the figure below:</div>
<div>
Figure 11.3</div>
<div>
CONNECTION MULTIPLEXING:</div>
<div>
In some circumstances transceiver may be in convenient e.g. workstations in a</div>
<div>
LAN. Connection multiplexer connects multiple computers to a single transceiver. Each</div>
<div>
computer’s AUI cable connects to connection multiplexer. One AUI from multiplexer to</div>
<div>
Ethernet coax. Connection multiplexing is shown in the figure below.</div>
<div>
Figure 11.4</div>
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<div>
THIN ETHERNET WIRING:</div>
<div>
Thin Ethernet uses thin coax cable that is cheaper and easier to install than thick</div>
<div>
Ethernet coax. In this case transceiver electronics are built into NIC and NIC connects</div>
<div>
directly to network medium.</div>
<div>
Coax cable use BNC connector on NIC. Coax runs directly to back of each</div>
<div>
connected computer by T-connector. The T-connector directly attaches to NIC. This is</div>
<div>
shown in the figure below.</div>
<div>
Figure 11.5</div>
<div>
Thin Ethernet is useful when many computers are located close to each other. It may be</div>
<div>
unreliable because any disconnection disrupts entire net.</div>
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<div>
Lecture No. 12</div>
<div>
LAN WIRING AND PHYSICAL TOPOLOGY</div>
<div>
10BASE-T:</div>
<div>
This is another standard of wiring scheme. It is commonly called 10Base-T,</div>
<div>
Twisted Pair or TP Ethernet. It replaces AUI cable with twisted pair cable and thick coax</div>
<div>
with hub.</div>
<div>
This makes it cheaper and that ‘s why it is most useful technology of today. It is</div>
<div>
shown in the figure below:</div>
<div>
Figure12.1</div>
<div>
HUBS:</div>
<div>
They are used for extension of connection with multiplexing concept. They are</div>
<div>
sometimes called Ethernet-in-a-box. It is effectively a very short Ethernet with very long</div>
<div>
AUI cables. It can be connected into larger Ethernet.</div>
<div>
PROTOCOL SOFTWARE AND ETHERNET WIRING:</div>
<div>
All wiring technologies use identical Ethernet specifications. e.g. they use same</div>
<div>
frame format. They use same CSMA/CD algorithms. They can mix different technologies</div>
<div>
in an Ethernet.</div>
<div>
NICs can provide all three-connection technologies. The protocol software can’t</div>
<div>
differentiate among wiring technologies. The NIC is shown in the figure below with three</div>
<div>
connectors.</div>
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<div>
Figure 12.2</div>
<div>
COMPARISON OF WIRING SCHEME:</div>
<div>
The wiring schemes are compared as follows:</div>
<div>
Separate transceiver allows computers to be powered off or disconnected from</div>
<div>
network without disrupting other communication.</div>
<div>
Transceiver may be located in an inconvenient place, so finely malfunction</div>
<div>
transceiver can be hard.</div>
<div>
In other case, thin coax cable takes minimum of cable. Disconnecting one computer (on</div>
<div>
one loose connection) can disrupt entire network.</div>
<div>
Hub wiring centralizes electronics and connections. It makes management easier.</div>
<div>
Bottom line 10Base-T is most popular because of lowest cost.</div>
<div>
TOPOLOGIES AND NETWORK TECHNOLOGIES:</div>
<div>
10Base-T network topology is a bus but wiring topology is a star. The token ring</div>
<div>
network topology is a ring but wiring topology is a star.</div>
<div>
We should remember to distinguish between logical and physical topologies. A</div>
<div>
topology is logically a star or it is physically a star.</div>
<div>
FILTERING INCOMING FRAMES:</div>
<div>
An analyzer can be configured to filter and process frames. It can count frames of</div>
<div>
a specific type or size. It can also display only frames from or to specific computers.</div>
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<div>
In general, it can be configured to match value of any field and capture only those</div>
<div>
frames making the filter specification.</div>
<div>
ADVANTAGE AND DISADVANTAGE OF WIRING</div>
<div>
SCHEMES:</div>
<div>
Each of three wiring schemes has advantages and disadvantages, which are</div>
<div>
explained as follows:</div>
<div>
RELIABILITY ISSUES:</div>
<div>
Wiring that uses a transceiver for each connection does not affect the entire</div>
<div>
network if a transceiver cable is disconnected. A cable cut occurring in hub wiring only</div>
<div>
affects one computer.</div>
<div>
COST ISSUES:</div>
<div>
Twisted pair Ethernet is the cheapest wiring that makes it so popular. Thicknet is</div>
<div>
the most costly wiring, which is no longer used.</div>
<div>
Figure 12.3</div>
<div>
As shown in the figure eight offices are wired with</div>
<div>
a) Thick Ethernet b) Thin Ethernet c) Twisted pair Ethernet</div>
<div>
We can see that the length of wired varies in three schemes so cost varies in three</div>
<div>
schemes.</div>
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<div>
THE TOPOLOGY PARADOX:</div>
<div>
The main feature of twisted pair Ethernet is that it forms a classic star topology</div>
<div>
however functions like a bus. 10Base-T Ethernet is often called a star shaped bus.</div>
<div>
Two different types OF TOPOLOGIES:</div>
<div>
LOGICAL TOPOLOGY:</div>
<div>
It is defined by the specific network technology.</div>
<div>
PHYSICL TOPOLOGY:</div>
<div>
It depends on the wiring scheme.</div>
<div>
NETWORK INTERFACE CARD AND WIRING SCHEMES:</div>
<div>
Figure 12.4</div>
<div>
To allow changing the wiring without changing the interface hardware, NICs support</div>
<div>
multiple wiring schemes. it is shown in the figure below.</div>
<div>
10/100 NETWORK INTERFACES AND AUTONEGATIATION:</div>
<div>
10Base-T version of twisted pair Ethernet operated at 10Mbps. 10Base-T Twisted</div>
<div>
pair Ethernet operates at 100Mbps.</div>
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<div>
100Base-T technology is backward compatible and allows the participants to negotiate a</div>
<div>
speed when connection is established. This process is known as auto negotiation.</div>
<div>
CATEGORIES OF WIRES:</div>
<div>
Cable used for wiring should match the following:</div>
<div>
• The intended data rate</div>
<div>
• The distance between devices</div>
<div>
• The amount of em-noise</div>
<div>
• Anticipated future needs</div>
<div>
• Cost</div>
<div>
Some categories and their typical uses are shown in the figure below.</div>
<div>
Figure 12.5</div>
<div>
WIRING SCHEMES AND OTHER NETWORK TECHNOLOGIES:</div>
<div>
Multiple wiring schemes are not limited to Ethernet technology. Almost alltogether</div>
<div>
network technologies use different wiring schemes. e.g., local talk uses hubs</div>
<div>
(physical star) to simulate a bus topology.</div>
<div>
IBM’s token ring also uses hubs (physically a star topology) to simulate a logical ring</div>
<div>
network.</div>
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<div>
Lecture No. 13</div>
<div>
FIBER MODEMS AND REPEATOERS</div>
<div>
LAN technologies are designed to operate within the same building. However</div>
<div>
most companies or institutions have offices located far apart from each other.</div>
<div>
DISTANCE LIMITATION AND LAN DESIGN:</div>
<div>
The maximum cable length of a LAN is fixed because the electrical signal level</div>
<div>
gets weaker as it travels. The delays must be short to allow access mechanisms</div>
<div>
(CSMA/CD, token passing) work properly.</div>
<div>
However in most cases a LAN needs to be extended layer distances than the</div>
<div>
maximum Cable length limit.</div>
<div>
For example: extending a company LAN to another building.</div>
<div>
LAN EXTENSIONS:</div>
<div>
Several techniques extend diameter of LAN medium. In this purpose most</div>
<div>
techniques use additional hardware. LAN signals relayed between LAN segments.</div>
<div>
Resulting mixed technology stays within original engineering constraints while</div>
<div>
spanning greater distance.</div>
<div>
FIBER OPTIC EXTENSION:</div>
<div>
The LAN extension using fiber optic is shown in the figure below:</div>
<div>
Figure 13.1</div>
<div>
The fiber-modem coverts digital data into pulses of light then transmits over the optical</div>
<div>
fiber. It also receives light and converts into digital data.</div>
<div>
This mechanism will successfully extend the optical fiber across several</div>
<div>
kilometers because delays on optical fiber are very low and bandwidth is very high.</div>
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<div>
REPEATERS:</div>
<div>
Repeaters are used when copper wire communication is carries out. According to</div>
<div>
the fact that electrical signal gets weaker while traveling over copper wires. A repeater is</div>
<div>
used to increase the signal strength. It amplifies the weakening signal received from one</div>
<div>
segment and then retransmits onto another segment.</div>
<div>
It is shown in the figure below:</div>
<div>
Figure13.2</div>
<div>
One repeater doubles, two repeaters triple the maximum cable length limitation.</div>
<div>
Computers attached to different segments communicate as if they are connected</div>
<div>
to the same cable.</div>
<div>
It is to be noted that we cannot increase the maximum cable length as many times</div>
<div>
as we wish by just adding repeaters. The reason for this is that every repeater introduces a</div>
<div>
delay and the access mechanism such as CSMA/CD does not work with long delays.</div>
<div>
Ethernet standard specifies that any two stations cannot be separated by more than</div>
<div>
four repeaters.</div>
<div>
Figure13.3</div>
<div>
The figure shows repeaters using the vertical segment. We see that only two repeaters</div>
<div>
separate any two stations in this scheme.</div>
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<div>
DISADVANTAGES OF REPEATERS:</div>
<div>
Repeaters do not recognize frame formats, they just amplify and retransmit the</div>
<div>
electrical signal. If a collision or error occurs in one segment, repeaters amplify and</div>
<div>
retransmit also the error onto the other segments.</div>
<div>
BRIDGES:</div>
<div>
A bridge is a hardware device also used to connect two LAN segments to extend a</div>
<div>
LAN. Unlike a repeater, a bridge uses two NICs to connect two segments. It listens to all</div>
<div>
traffic and recognizes frame format. It also forwards only correct complete frames and</div>
<div>
discards the collided and error frames.</div>
<div>
A typical bridge has two NICs, a CPU a memory and a ROM. It only runs the</div>
<div>
code stored in its ROM.</div>
<div>
FRAME FILTERING:</div>
<div>
The most important task a bridge performs is frame filtering. If both the source</div>
<div>
and destination are on the same segment, it does not forward the frame to the other</div>
<div>
segment. A frame is forwarded to the other segment, if it id destined to that segment.</div>
<div>
Broadcast and multicast frames are also forwarded.</div>
<div>
A bridge keeps a list for each segment that consists of physical addresses of the</div>
<div>
computer attached to that segment. In this way a bridge knows on which segment a</div>
<div>
destination computer is attached.</div>
<div>
Most bridges are self learning bridges. As soon as a frame arrives to a bridge, it</div>
<div>
extracts a source address from its header and automatically adds it in the list for that</div>
<div>
segment. In this way a bridge builds up address lists. This is shown in the figure below:</div>
<div>
Figure 13.4</div>
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Lecture No. 14</div>
<div>
BRIDGES</div>
<div>
STARTUP AND STEADY STATE:</div>
<div>
When a bridge first boots the address lists are empty (start up state). The bridge</div>
<div>
forwards frames to the other segment if it can not find its destination address in its lists.</div>
<div>
After some time when the bridge has received at least one frame from every</div>
<div>
computer, it has the lists built (steady state) it forwards frames as far it is necessary.</div>
<div>
PLANNING A BRIDGE NETWORK:</div>
<div>
In a steady state, a bridge allows simultaneous use of each segment. When</div>
<div>
designing a LAN, bridges can be installed to divide the LAN into segments to improve</div>
<div>
performance.</div>
<div>
For example:</div>
<div>
Frequently contacting computers can be attached to the same segment. The frame</div>
<div>
traffic on one segment does not affect the other segments.</div>
<div>
BRDGING BETWEEN BUILDINGS:</div>
<div>
If two buildings are located far from each other, a bridge, a pair of fiber modems</div>
<div>
and an optical fiber can be used to connect two LANs as shown in the figure below.</div>
<div>
Figure14.1</div>
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<div>
BRIDGING BETWEEN BUILDINGS:</div>
<div>
ADVANTAGES:</div>
<div>
COST:</div>
<div>
An optical fiber modem pair is sufficient to connect many computers located on</div>
<div>
separate buildings.</div>
<div>
MAINTAINANCE:</div>
<div>
There is no need to change the wiring between the buildings when installing and</div>
<div>
removing a computer.</div>
<div>
PERFORMANCE:</div>
<div>
The traffic on each building does not affect the other.</div>
<div>
BUIDING ACROSS LONGER DISTANCES:</div>
<div>
It is not always possible to connect two sites with optical fiber because the</div>
<div>
distance may be too long. It is usually not allowed to lay an optical fiber if the land does</div>
<div>
not belong to you.</div>
<div>
There are two common methods to connect two distant sites.</div>
<div>
LEASED SERIAL LINE CONNECTION: Which is less distant.</div>
<div>
LEASED SATELLITE CHANNEL:</div>
<div>
It can span arbitrarily long distance. It is shown in the figure below.</div>
<div>
Figure14.2</div>
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<div>
Unlike optical fibers, satellite connections are low bandwidth to save cost.</div>
<div>
Because the frames arrived from local network are much faster than they can be sent</div>
<div>
across a satellite link.</div>
<div>
The bridge must use buffering (saving a copy of frame into memory until it can be</div>
<div>
sent). It may run out of memory. The communication software usually waits for a</div>
<div>
response after sending a few frames.</div>
<div>
A CYCLE OF BRIDGES:</div>
<div>
A bridges network can connect many segments. One bridge is needed to connect</div>
<div>
each segment to the rest of the bridge network. This is shown in the figure below:</div>
<div>
Figure14.3</div>
<div>
If the bridges on the longer network form a cycle, then broadcasting frames introduce a</div>
<div>
problem i.e. the copies of broadcast frame continuously flows around the cycle (each</div>
<div>
computer receiving an infinite number of copies). This is shown below.</div>
<div>
Figure14.4</div>
<div>
DISTRIBUTED SPANNING TREE:</div>
<div>
If a bridge network forms a cycle, then not all bridges on the network must be</div>
<div>
allowed to forward broadcast frames.</div>
<div>
The bridges configure themselves automatically to decide which bridge will</div>
<div>
forward broadcast frames and which bridge will not.</div>
<div>
The bridges communicate with each other on the network and use Distributed</div>
<div>
Spanning Tree (DST) algorithm to decide which bridge will not forward frames if a cycle</div>
<div>
occurs.</div>
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<div>
Lecture No. 15</div>
<div>
SWITCHES AND WAN TECHNOLOGIES</div>
<div>
SWITCHING:</div>
<div>
A switched LAN consists of a single electronic device that transfers frames among the</div>
<div>
connected computers. A hub with multiple ports simulates a single shared medium.</div>
<div>
However a switch simulates a bridged LAN with one computer per segment.</div>
<div>
A switch is shown in the figure below.</div>
<div>
Figure 15.1</div>
<div>
If a hub is used to connect among computers on a LAN, then only two computers can</div>
<div>
communicate at a given time. However if a switch is used, the communication between</div>
<div>
two computers will not affect the other pair of computers. They can communicate at the</div>
<div>
same time.</div>
<div>
COMBINING SWITCHES AND HUBS:</div>
<div>
To reduce costs, computers can be connected and distributed to a number of hubs,</div>
<div>
and then the hubs can be connected to a switch. Hubs simulate single shared LAN</div>
<div>
segments and a switch simulates a bridged LAN connecting segments.</div>
<div>
BRIDGING AND SWITCHING WITH OTHER TECHNOLOGIES:</div>
<div>
Hubs, Bridges and Switches are not limited to Ethernet logical bus topology.</div>
<div>
They are available also for other networking technologies such as token ring, FDDI etc.</div>
<div>
like FDDI hub and Token ring hub.</div>
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<div>
WAN TECHNOLOGIES AND ROUTING;</div>
<div>
INTRODUCTION:</div>
<div>
LANs can be extended using techniques in previous chapter. They can not be</div>
<div>
extended arbitrarily for or to handle many computers. Because there are distance</div>
<div>
limitations even with extensions so we need other technologies for larger networks.</div>
<div>
CHARACTERIZATION OF NETWORKS:</div>
<div>
There are three types of characterization of networks.</div>
<div>
LOCAL AREA NETWORK (LAN):</div>
<div>
It is used for a single building.</div>
<div>
METROPOLOTAN AREA NETWORK (MAN):</div>
<div>
It is used for a single city.</div>
<div>
WIDE AREA NETWORK (WAN):</div>
<div>
It is used for a country level networking and even for continents.</div>
<div>
DIFFERENCE BETWEEN LAN AND WAN:</div>
<div>
Although LAN is for a local area but satellite bridge can extend LAN across large</div>
<div>
distances. But it still can’t accommodate arbitrarily many computers.</div>
<div>
On the other hand WAN must be scalable to long distances and many computers.</div>
<div>
PACKET SWITCHES:</div>
<div>
To span long distances or many computers, networks must replace shared</div>
<div>
medium with packet switches. Each switch moves an entire packet from one connection</div>
<div>
to another. That’s why they are called packet switches. A packet switch consists of a</div>
<div>
small computer with network interfaces, a memory and a program dedicated to packet</div>
<div>
switching function.</div>
<div>
A packet switch is shown in the figure below.</div>
<div>
Figure 15.2</div>
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<div>
CONNECTION TO PACKET SWITCHES:</div>
<div>
A packet switch many connect to computers and to other packet switches. But the</div>
<div>
speeds are different in both cases. There are typically high-speed connections to other</div>
<div>
packet switches but lower speed connections to the computers. The technology details</div>
<div>
depend upon desired speed.</div>
<div>
PACKET SWITCHES AS A BUILDING BLOCKS:</div>
<div>
Packet switches can be linked together to form WAN. WAN need not be</div>
<div>
symmetric or have regular connections. Each switch may connect to one or more other</div>
<div>
switches and one or more other computers as shown in the figure below.</div>
<div>
Figure 15.2</div>
<div>
STORE AND FORWARD:</div>
<div>
Data delivery from one computer to another is accomplished through store and</div>
<div>
forward technology. In this technology packet switch stores incoming packet and also</div>
<div>
forwards that packet to another switch or computer. For this purpose packet switch has</div>
<div>
internal memory into which it can hold packet if outgoing connection is busy. Packets for</div>
<div>
each connection held on queue.</div>
<div>
PHYSICAL ADDRESSING IN A WAN:</div>
<div>
The physical addressing in a WAN is similar as in LAN in the following way:</div>
<div>
• The data is transmitted in packets equivalent to frames.</div>
<div>
• Each packet has a format with header.</div>
<div>
• The packet header includes destination and source addresses.</div>
<div>
• Many WANs use hierarchical addressing for efficiency. One part of address</div>
<div>
identifies destination switch. Other part of address identifies port on switch. This is</div>
<div>
shown in the figure below.</div>
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<div>
Figure 15.4</div>
<div>
NEXT HOP FORWARDING:</div>
<div>
Packet switch must choose outgoing connection for forwarding the packet. There</div>
<div>
are two cases.</div>
<div>
• If the destination is local computer, packet switch delivers computer port.</div>
<div>
• If the destination is attached another switch, this packet switch forwards to next</div>
<div>
hop through connection to another switch.</div>
<div>
• The choice of another switch is based on destination address in packet.</div>
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<div>
Lecture No. 16</div>
<div>
ROUTING</div>
<div>
SOURCE INDEPENDENCE:</div>
<div>
Next hop to destination does not depend on source of packet. This phenomenon is</div>
<div>
called ‘Source Independence’. It has several benefits. It allows fast and efficient routing.</div>
<div>
Packet switch need not hove complete information about all destinations in spite it just</div>
<div>
has next hop so reduces total information and increases dynamic robustness. The network</div>
<div>
can continue to function even if topology changes without notifying entire network.</div>
<div>
HIERARCHICAL ADDRESSING AND ROUTING:</div>
<div>
The process of forwarding the packets of information is called routing. The</div>
<div>
information about destinations is kept in routing tables. Note that many entries have same</div>
<div>
next hop. It is shown in the figure.</div>
<div>
Figure 16.1</div>
<div>
In particular all destinations on same switch have same next hop. These routing</div>
<div>
tables can be collapsed. A specific routing table is shown in the figure.</div>
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<div>
Figure 16.2</div>
<div>
ROUTING IN A WAN:</div>
<div>
As there will be more computers there will be more traffic of information. We can</div>
<div>
add capacity to WAN by adding more links and packet switches. Packet switches need</div>
<div>
not have computers attached. There are two types of switch according to the attached</div>
<div>
computers.</div>
<div>
INTERIOR SWICH:</div>
<div>
The switch that has no attached computers is called an interior switch.</div>
<div>
EXTERIOR SWITCH:</div>
<div>
The switch that has computers attached with it is called exterior switch.</div>
<div>
Both interior and exterior switches forward packets and they also need routing tables. The</div>
<div>
routing table must have two things.</div>
<div>
UNIVERSAL ROUTING:</div>
<div>
It should have next hop for each possible destination.</div>
<div>
OPTIMAL ROUTES:</div>
<div>
The next hop in table must be on shortest path to destination.</div>
<div>
MODELING A WAN:</div>
<div>
To model a WAN, we use a graph in which the nodes model switches and the</div>
<div>
edges model direct connection between switches. The modeling captures essence of</div>
<div>
network and it ignores attached computers as shown in the figure below. Modeling of a</div>
<div>
specific WAN is shown.</div>
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<div>
Figure 16.3</div>
<div>
ROUTE COMPUTATION WITH A GRAPH:</div>
<div>
We can represent routing table with edges as shown in the figure below:</div>
<div>
Figure 16.4</div>
<div>
The graph algorithms can be applied to find routes.</div>
<div>
REDUNDANT ROUTING INFORMATION:</div>
<div>
Notice duplication of information in routing table for node 1 as shown above in</div>
<div>
the figure. We see that switch has only outgoing connection, all traffic must traverse that</div>
<div>
connection.</div>
<div>
DEFAULT ROUTES:</div>
<div>
Routing table entries can be collapsed with a default route. If the destination does</div>
<div>
not have in explicit routing table entry, then it use a default route. Default routes for 4</div>
<div>
nodes are shown in the figure below.</div>
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<div>
Figure 16.5</div>
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<div>
Lecture No. 17</div>
<div>
ROUTING ALGORITHMS</div>
<div>
BUILDING ROUTING TABLES:</div>
<div>
There are basically two methods for building routing tables, which are as follows:</div>
<div>
• Manual entry</div>
<div>
• Software</div>
<div>
Further there are two methods for computing routing table information.</div>
<div>
• Static routing</div>
<div>
• Dynamic routing</div>
<div>
STATIC ROUTING:</div>
<div>
It is done at boot time. It is simple and has low network overhead. It is inflexible.</div>
<div>
DYNAMIC ROUTING:</div>
<div>
It allows automatic updates by a programmer. It can work around network failures</div>
<div>
automatically.</div>
<div>
COMPUTING SHORTEST PATH IN A GRAPH:</div>
<div>
While computing shortest path, first we assume graph representation of network</div>
<div>
at each node then we use Djikstra’s algorithm to compute shortest path from each node to</div>
<div>
every other node. Then extract next hop information from resulting path information and</div>
<div>
insert next hop information into routing tables.</div>
<div>
WEIGHTED GRAPH:</div>
<div>
Djikstra’s algorithm can accommodate weights on edges in graph. The shortest</div>
<div>
path is then the path with lowest total weight (sum of the weight with all edges). It should</div>
<div>
be noted that the shortest path is not necessarily with fewest edges (or hops). For example</div>
<div>
as shown in the figure below:</div>
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<div>
Figure 17.1</div>
<div>
The shortest path in the figure from node 2 to node 6 is 2 to 3 and 3 to 6 as this</div>
<div>
path has the smallest weight so it is the shortest path.</div>
<div>
DISTANCE MATRICS:</div>
<div>
Weights on graph edges reflect cost of traversing edge. This cost may be in time,</div>
<div>
dollars or hop counting (weight == 1). The resulting shortest path may not have fewest</div>
<div>
hops.</div>
<div>
DISTRIBUTED ROUTE COMPUTATION:</div>
<div>
Each packet switch computes its routing table locally and sends messages to the</div>
<div>
neighbors. It also updates information periodically. If a link or a packet switch fails then</div>
<div>
the network adapts its failure. The packet switch then modifies the tables to avoid failed</div>
<div>
hardware.</div>
<div>
DISTANCE-VECTOR ROUTING:</div>
<div>
Local information is next hop routing table and distance from each switch. The</div>
<div>
switches periodically broadcast topology information i.e. destination, distance.</div>
<div>
Other switches update routing table based on received information.</div>
<div>
VECTOR-DISTANCE ALGORITHM:</div>
<div>
It is explained in more detail below:</div>
<div>
Packet switches wait for next update message and they iterate through entries in</div>
<div>
message. If entry has shortest path to destination, insert source as next hop to destination</div>
<div>
and record distance as distance from next hop to destination plus distance from this</div>
<div>
switch to next hop.</div>
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<div>
LINK-STATE ROUTING:</div>
<div>
In link-state routing network topology is separated from route computation.</div>
<div>
Switches send link-state information about local connections. Each switch builds own</div>
<div>
routing tables. It uses link-state information to update global topology and runs Djikstra’s</div>
<div>
algorithm.</div>
<div>
COMPARISON:</div>
<div>
DISTANCE-VECTOR ROUTING:</div>
<div>
• It is very simple to implement.</div>
<div>
• Packet switch updates its own routing table first.</div>
<div>
• It is used in RIP.</div>
<div>
LINK-STATE ALGORITHM:</div>
<div>
• It is much more complex.</div>
<div>
• Switches perform independent computations.</div>
<div>
• It is used in OSPF.</div>
<div>
EXAMPLE WAN TECHNOLOGIES:</div>
<div>
Some multiple WAN technologies are discussed below.</div>
<div>
ARPANET:</div>
<div>
It began in 1960’s. It was funded by Advanced Research Project Agency, which is</div>
<div>
an organization of US defense department. It was incubator for many of current ideas,</div>
<div>
algorithms and Internet technologies.</div>
<div>
X.25:</div>
<div>
It was early standard for connection-oriented networking. It began from IFU,</div>
<div>
which was originally CCITT. It predates computer connections, which are used for</div>
<div>
terminal/time sharing connection.</div>
<div>
FRAME RELAY:</div>
<div>
It is used for Telco service for delivering blocks of data. It is connection based</div>
<div>
service and must contract with Telco for circuit between two endpoints. It is typically</div>
<div>
56kbps or 1.5Mbps and can run to 100Mbps.</div>
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<div>
SMDS:</div>
<div>
Switched Multi megabit Data Service (SMDS) is also a Telco service. It is a</div>
<div>
connection less service. Any SMDS station can send information to any station on the</div>
<div>
same SMDS cloud. It is typically ranges from 1.5Mbps to 1000Mbps.</div>
<div>
ATM (ASYNCHRONOUS TRANSFER MODE):</div>
<div>
It was designed as a single technology for voice, video and data and has low jitter</div>
<div>
(variance in delivery time) and high capacity.</div>
<div>
It uses fixed size, small cells, 48 octet’s data and 5 octets header. It can also</div>
<div>
connect multiple ATM switches into a network.</div>
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<div>
Lecture No. 18</div>
<div>
CONNECTION-ORIENTED NETWORKING AND</div>
<div>
ATM</div>
<div>
LANs and WANs can both connect multiple computers, but they have different</div>
<div>
base technologies and meet different goals. ATM is a single technology that is designed</div>
<div>
to meet the goals of both LANs and WANs.</div>
<div>
ATM uses the concept of connection-oriented networking.</div>
<div>
ASYNCHRONOUS TRANSFER MODE (ATM):</div>
<div>
Telephone companies (Telco’s) introduced ATM to meet several goals. It</div>
<div>
provides universal service for all subscribers and support for all users for voice, video</div>
<div>
and data. It has a single unified infrastructure (no separate LANs and WANs). It gives</div>
<div>
guaranteed service when it is appropriate and support for low cost devices.</div>
<div>
JITTER:</div>
<div>
Jitter is the term used for variance in transmission delays.</div>
<div>
Jitter is significance for voice, video and data. In LANs, jitter can occur when a packet is</div>
<div>
delayed because the network is busy.</div>
<div>
PACKET SIZES:</div>
<div>
Large packets result in fewer overheads because a smaller fraction of the packet is</div>
<div>
used for header information.</div>
<div>
Optimum networks use 4kB packets or larger.</div>
<div>
Large packets can’t easily be used for voice for example 8-bit samples (at</div>
<div>
125usec per sample) would require half a second to fill a 4kB packet. Echo cancellation</div>
<div>
can only be used with low transmission delays.</div>
<div>
ATM CELLS:</div>
<div>
To meet its goals, ATM uses small, fixed sized packets called cells. Each cell has</div>
<div>
53 octets. VPI/VCI fields identify the cells destination.</div>
<div>
PRIO tell if cell can be discarded CRC checks the header bits only. ATM header</div>
<div>
is about the 10% of the cell. Ethernet can have overhead of only 1%. Engineers</div>
<div>
sometimes call the ATM overhead the cell tax. An ATM is shown below.</div>
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<div>
Figure.18.1</div>
<div>
CONNECTION-ORIENTED SERVICE:</div>
<div>
The connection-oriented service paradigm for networking is similar to the</div>
<div>
manner in which telephones are used. This is given as follows:</div>
<div>
A caller dials a number of the destination. The telephone at the destination signals</div>
<div>
the arrival of a connection request. If the called person does not answer; the caller gives</div>
<div>
up after waiting for a timeout. If the called person does answer, then the connection is</div>
<div>
established.</div>
<div>
In data communication, as binary connection identifier is given to each of the two</div>
<div>
parties to enable identification of the connection.</div>
<div>
VIRTUAL CHANNEL (OR CIRCUITS):</div>
<div>
Connections in ATM are called virtual channels (VC) or virtual circuits (a term</div>
<div>
preferred by some). These are called virtual, since connections are formed in ATM by</div>
<div>
starting values in memory locations (tables) in ATM switches as opposed to making</div>
<div>
actual electrical connections.</div>
<div>
The VC is identified by a 24-bit value formed from the VPI or Virtual Path Indicator (8-</div>
<div>
bit), which identifies a particular path through the network and the VCI or Virtual</div>
<div>
Channel Indicator (16-bits), which identifies the channel in the virtual path being used by</div>
<div>
the connection.</div>
<div>
Most frequently, the 24-bit pair is treated as just a single connection identifier by</div>
<div>
computers.</div>
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Lecture No. 19</div>
<div>
ATM: VIRTUAL CIRCUITS</div>
<div>
LABELS AND LABEL SWITCHING:</div>
<div>
An ATM network is built from interconnected ATM switches. The attachment</div>
<div>
points or ports can be connected to computers or other ATM switches. As cells arrive at</div>
<div>
an ATM switch, their VPI/VCI is modified using a forwarding table that gives the new</div>
<div>
VPI/VCI for the next leg of the cell’s trip.</div>
<div>
The forwarding table is essentially indexed by the incoming cell’s VPI/VCI and</div>
<div>
the contents yield the new VPI/VCI.</div>
<div>
LABEL REWRITING:</div>
<div>
The replacement of the incoming cell’s VPI/VCI with a probably different</div>
<div>
VPI/VCI is called rewriting.</div>
<div>
ATM is thus called a label rewriting or label switching system. Thus two</div>
<div>
computers with a connection through an ATM network will likely have different</div>
<div>
VPI/VCI values for each end of the connection as shown in the figure below.</div>
<div>
Figure 19.1</div>
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<div>
Figure 19.2</div>
<div>
EXAMPLE:</div>
<div>
As an example, in the figure we see that the sending computer S uses a VPI/VCI</div>
<div>
of 3 and sends a cell.</div>
<div>
Switch A receives the cell and looks up 3, then rewrites the VPI/VCI as 4, and</div>
<div>
sends the cell out of its port 2.</div>
<div>
Switch B receives the cell and looks up 4 then rewrites the VPI/VCI as 1 and</div>
<div>
sends the cell at its port 2.</div>
<div>
Switch C receives the cell and looks up 1 then rewrites the VPI/VCI as 6 and</div>
<div>
sends the cell out of its port 2.</div>
<div>
The receiving computer R receives the cell with a VPI/VCI of 6, which is the</div>
<div>
value it is using for the connection. Forwarding tables in each switch must be coordinated</div>
<div>
to define meaningful ‘paths’ through the network.</div>
<div>
PERMANENT VIRTUAL CIRCUITS:</div>
<div>
ATM can provide customers with virtual circuits that look like traditional leased</div>
<div>
digital circuits. Such permanent virtual circuits (PVC) last as long as the customer pay</div>
<div>
the periodic fee for its use. The forwarding tables are automatically restored after power</div>
<div>
of equipment failure. The forwarding table entries for such permanent VC’s are statically</div>
<div>
configured, the terms used by Telco’s for this is provisioning.</div>
<div>
Provisioning requires two steps:</div>
<div>
1. To determine a complete path (that is, identify the switches that will be used).</div>
<div>
2. To choose appropriate VPI/VCI for each step in the path, and configure each</div>
<div>
adjacent pair of switches (easy, since each switch rewrites the VCI/VPI).</div>
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<div>
SWITCHED VIRTUAL CIRCUITS:</div>
<div>
Most networks offer dynamic connections, which last for a relatively short time.</div>
<div>
To handle this, ATM can dynamically establish a switched virtual circuit (SVC), allow it</div>
<div>
last as long as necessary and then terminate it.</div>
<div>
The terminology comes from the Telco’s where switching system normally refers</div>
<div>
to all switching.</div>
<div>
ESTABLISHING AN SVC:</div>
<div>
The computer sends a connection request to the switch to which it is attached.</div>
<div>
Software in the switch finds a network path to the destination and sends along the</div>
<div>
connection request.</div>
<div>
Each pair of switches in the path communicates to choose a VPI/VCI for their</div>
<div>
tables. Once the connection is established by the destination, a message is sent back to</div>
<div>
the originating computer to indicate the SVC is ready.</div>
<div>
If any switch or the destination computer does not agree to setting up the VC, an</div>
<div>
error message is sent back and the SVC is not established.</div>
<div>
SIGNALING:</div>
<div>
The term signaling is used to describe communication about the network, as</div>
<div>
opposed to communication that just uses the network.</div>
<div>
A computer uses signaling with reserved VCI/VPI values to communicate with a</div>
<div>
switch to establish a connection or send other network control messages. These</div>
<div>
connection requests and network control messages are also sent in cells and since the</div>
<div>
VPI/VCI use in these cells are reserved there is no confusion between data and control</div>
<div>
cells.</div>
<div>
QUALITY OF SERVICE:</div>
<div>
Networks are more frequently being designed to allow specification of the quality</div>
<div>
of service required by users.</div>
<div>
For example: - a typical voice telephone call might give a QoS parameter for throughput</div>
<div>
of 64kbps and delay less than 500msec. A user sending video might require throughput of</div>
<div>
2Mbps.</div>
<div>
PROVIDING DESIRED QoS:</div>
<div>
QoS desires are specified at connection setup time and one never altered for the</div>
<div>
connection duration. Switches along the path must reserve resources to guarantee the</div>
<div>
QoS.</div>
<div>
If a switch cannot provide the resources, it rejects the connection requests and an</div>
<div>
appropriate error message is returned.</div>
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<div>
ATM QoS SPECIFICATIONS:</div>
<div>
There are three types of QoS specifications, which are given as follows:</div>
<div>
CONSTANT BIT RATE (CBR):</div>
<div>
It is used for audio and video, since these have predefined maximum data rates.</div>
<div>
VARIABLE BIT RATE (VBR):</div>
<div>
It is used for compressed audio and video where the data rate depends on the level</div>
<div>
of compression that can be achieved.</div>
<div>
AVAILABLE BIT RATE (ABR):</div>
<div>
It is used for typical data applications (where the data rate may be unknown and</div>
<div>
bursty) and allows use of whatever bandwidth is available at a given time.</div>
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<div>
Lecture No. 20</div>
<div>
ATM AND NETWORK OWNERSHIP</div>
<div>
CELLS VS PACKETS:</div>
<div>
ATM designers chose cells over packets because of the following reasons:</div>
<div>
• Cells are not variable length and memory management for them is simpler.</div>
<div>
Handling variable length packets leads to memory fragmentation.</div>
<div>
• Variable length packets require hardware to accommodate the largest possible</div>
<div>
packet, and thus to detect the end of the packet. With cells bits can just be counted</div>
<div>
as they arrive.</div>
<div>
• The length of time required to send a variable length packet is variable and</div>
<div>
requires complicated interrupt scheme to detect completion of transmission. QoS</div>
<div>
can’t be guaranteed with variable length packets as easily as it can with fixed</div>
<div>
length cells.</div>
<div>
ATM SPEED:</div>
<div>
ATM designers also chose cells to meet the need for speed. Since it was designed</div>
<div>
to handle arbitrarily large numbers of users, each of which could be willing to pay for</div>
<div>
high throughput.</div>
<div>
ATM is designed to work on fiber (but can be used with twisted pair). A typical</div>
<div>
port on an ATM switch operates at OC-3 speed (155Mbps) or higher.</div>
<div>
ATM CRITIQUE:</div>
<div>
ATM is far more expensive than typical LAN hardware. Connection setup time</div>
<div>
may be excessive for short communications. Cell tax consumes 10% of network capacity</div>
<div>
QoS requirements might be unknown, leading to applications picking values that are too</div>
<div>
high or too low.</div>
<div>
Broadcast is inefficient and has to be simulated by sending the same message to</div>
<div>
each computer separately.</div>
<div>
ATM as a single universal networking technology has only minimal provision for</div>
<div>
interoperation with other technologies.</div>
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<div>
NETWORK OWNERSHIP:</div>
<div>
There are two categories in this case:</div>
<div>
PRIVATE NETWOK:</div>
<div>
Single organization or company owns this. They are often LAN technologies.</div>
<div>
There can be multiple LANs in a building or campus linked together. They are sometimes</div>
<div>
called Intranet.</div>
<div>
PRIVATE NETWORK ARCHITECTURE:</div>
<div>
It operates autonomously from other networks (e.g. internet).</div>
<div>
It usually includes one or few closely managed external connections. They may restrict</div>
<div>
access at connections.</div>
<div>
MANAGING PRIVATE NETWORKS:</div>
<div>
An organization buys its own equipment and hires staff to design, implement,</div>
<div>
maintain and upgrade network. It is responsible for all network management.</div>
<div>
EXTENDING PRIVATE NETWORK:</div>
<div>
The large organizations may have multiple buildings or campuses. They can only</div>
<div>
install cables on their own property. They may contract for leased lines from common</div>
<div>
carrier.</div>
<div>
PUBLIC NETWORK:</div>
<div>
This is owned by common carrier e.g. Phone Company. The public networks are</div>
<div>
those networks, which are operated by common carriers. It may be a telephone company</div>
<div>
or another organization that builds network out of leases lines. Multiple organizations</div>
<div>
subscribe and connect. Data transits public network to other organizations.</div>
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<div>
ADVANTAGES AND DISADVANTAGES:</div>
<div>
The advantages and disadvantages of Public and Private Networks are given in the table</div>
<div>
below:</div>
<div>
NETWORKS ADVANTAGES DISADVANTAGES</div>
<div>
PUBLIC They are flexible. There are no decisionmaking</div>
<div>
equipment or</div>
<div>
policies.</div>
<div>
PRIVATE The owner has complete</div>
<div>
control over both the</div>
<div>
technical decision and</div>
<div>
policies.</div>
<div>
They are expensive to</div>
<div>
install and maintain.</div>
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Lecture No. 21</div>
<div>
NETWORK SERVICE PARADIGM</div>
<div>
VIRTUAL PRIVATE NETWORK:</div>
<div>
Virtual Private Network (VPN) combines the features of both private and public</div>
<div>
networks. It is limited to single organization and uses public network for connectivity.</div>
<div>
These connections are sometimes called tunnels and connect sites. Each site sees</div>
<div>
tunnel as point-to-point link. There is no access for other users of public networks.</div>
<div>
GUARANTEEING ABSOLUTE PRIVACY:</div>
<div>
In addition to restricting packets, VPN systems use encryption to guarantee</div>
<div>
absolute privacy. Even if an outside does manage to obtain a copy of the packet the</div>
<div>
outside will be unable to interpret the contents.</div>
<div>
SERVICE PARADIGM:</div>
<div>
At the lowest level most networks transfer individual packets of data and the</div>
<div>
network requires each packet to follow an exact format dictated by the hardware, which</div>
<div>
is called Interface paradigms or service paradigms.</div>
<div>
There are two types of service paradigms:</div>
<div>
CONNECTION-ORIENTED:</div>
<div>
It is similar to the telephone system: endpoints establish and maintain a</div>
<div>
connection as long as they have data to exchange.</div>
<div>
CONNECTIONLESS:</div>
<div>
Similar to postal system: endpoints put data to send into a packet and hand to</div>
<div>
network for delivery.</div>
<div>
CONNECTION-ORIENTED SERVICE:</div>
<div>
One endpoint requests connection from network. Other endpoint agrees to</div>
<div>
connection. Computers exchange data through connection. One-endpoint requests</div>
<div>
network to break connection when transmission is complete.</div>
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<div>
CONTINUOUS AND BURST TRAFFIC:</div>
<div>
Networks handling voice or video are engineered to accept and deliver continuous</div>
<div>
data at fixed rate. Others are designed to handle burst traffic typical of computer</div>
<div>
networks. Connection does not disappear when no data is sent.</div>
<div>
SIMPLEX & FULL DUPLEX CONNECTION:</div>
<div>
Some connection-oriented technologies provide full duplex while other allow on</div>
<div>
simplex connection. To communicate using a simplex design a pair of computers must</div>
<div>
establish two connections one from computer A to computer B and another from</div>
<div>
computer B to A.</div>
<div>
CONNECTION DURATION AND PERSISTANCE:</div>
<div>
Connection can be made on demand set up permanently. There are two types:</div>
<div>
• Switched Connection or Switched Virtual Circuit (SVC).</div>
<div>
• Permanent Connection or Permanent Virtual Circuit (PVC).</div>
<div>
Permanent connections are originally hardwired and now configured at system unit time.</div>
<div>
In switched connections, computer maintains permanent connection to network and</div>
<div>
networks make connections on demand. Internal components are switched networks is a</div>
<div>
switched data network.</div>
<div>
SERVICE GUARANTEES:</div>
<div>
Some connection-oriented networks provide guarantees about the service that</div>
<div>
computer will receive. They may guarantee a throughput rate maximum packet loss rate.</div>
<div>
For example, ATM provides statistical guarantee about performance.</div>
<div>
STREAM OR MESSAGE INTERFACE:</div>
<div>
Some connection-oriented networks provide stream interfaces. In which no</div>
<div>
boundaries are recorded that receiver may receive a single block of 60 characters.</div>
<div>
Others provide a message interface that delivers data in the same size chunks that</div>
<div>
the sender transmitted.</div>
<div>
CONNECTIONLESS SERVICE:</div>
<div>
In connectionless service, there is no connection necessary. The source of data</div>
<div>
adds destination information in data and delivers to the network. Network delivers each</div>
<div>
data item individually.</div>
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<div>
INTERIOR AND EXTERIOR SERVICE PARADIGM:</div>
<div>
A network providing one service paradigm to the attached computers can use an</div>
<div>
entirely different service paradigm internally.</div>
<div>
For example ARPANET is connection oriented internally and connectionless</div>
<div>
externally.</div>
<div>
COMPARISON:</div>
<div>
CONNECTION-ORIENTED:</div>
<div>
• Accounting is easier.</div>
<div>
• Application can learn of network problems immediately.</div>
<div>
CONNECTIONLESS:</div>
<div>
• It has fewer overheads.</div>
<div>
• It is easier to implement network.</div>
<div>
An example of service paradigm is shown in the figure below.</div>
<div>
Figure 21.1</div>
<div>
ADDRESSES AND CONNECTION IDENTIFIERS:</div>
<div>
Address is a complete unique identifier. Connectionless delivery requires address</div>
<div>
on each packet.</div>
<div>
Connection-oriented delivery can use a short hand that identifies the connection</div>
<div>
rather than the destination.</div>
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<div>
As an example let’s consider an ATM with 16-bit address, 24-bit connection</div>
<div>
identifier and connection identifier includes.</div>
<div>
-8-bit Virtual Path Identifier (VPI)</div>
<div>
-16-bit Virtual Circuit Identifier (VCI)</div>
<div>
The connection identifier is local to each computer and it may be different at</div>
<div>
different parts of the ATM switch.</div>
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<div>
Lecture No. 22</div>
<div>
NETWORK PERFORMANCE</div>
<div>
There are two types of characteristics in case of network performance.</div>
<div>
• Delay</div>
<div>
• Throughput</div>
<div>
DELAY:</div>
<div>
It is an important quantitative property of networks. Delay is a measure how long</div>
<div>
it takes for a bit of data to travel across the network from one compute to the other.</div>
<div>
It is measured in seconds or fractions of seconds.</div>
<div>
TYPES OF DELAY:</div>
<div>
There are following types of delay:</div>
<div>
PROPAGATION DELAY:</div>
<div>
It defined as the time to travel across medium.</div>
<div>
SWITCHING DELAY:</div>
<div>
It is the time required for network component (hub, bridge, packet switch) to</div>
<div>
forward data.</div>
<div>
ACCESS DELAY:</div>
<div>
It is the time required to get control of medium (CSMA/CD, token).</div>
<div>
QUEUING DELAY:</div>
<div>
It is the time enquired in packet switches.</div>
<div>
THROUGHPUT:</div>
<div>
Throughput is a measure of the rate at which data can be sent through the</div>
<div>
network. The throughput capability of the underlying hardware is called bandwidth.</div>
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<div>
Because each frame contains headers, the effective throughput is less than the hardware</div>
<div>
bandwidth.</div>
<div>
Networking professional often use the term speed as a synonym for throughput.</div>
<div>
RELATIONSHIP BETWEEN DELAY AND THROUGHPUT:</div>
<div>
If a packet switch has a queue of packets waiting when a new packet arrives. The</div>
<div>
new packet will be placed on the entire queue and will need to wait while the switch</div>
<div>
forwards the previous packets.</div>
<div>
Throughput and delay are not completely independent. As traffic in a computer</div>
<div>
network increase, delays increase a network that operates at close to 100% of its</div>
<div>
throughput capacity experiences severe delay.</div>
<div>
DELAY THROUPUT PRODUCT:</div>
<div>
It is computed as delay time multiplied by effective throughput. It measures</div>
<div>
amount of data that can be present in the network. In fast network with long delay times,</div>
<div>
sending computer can generate large amounts of data before destination receives first bit.</div>
<div>
JITTER:</div>
<div>
The amount of delay that a network introduces is called jitter. A network with</div>
<div>
zero jitter takes exactly the same amount of time to transfer each packet. A network with</div>
<div>
high jitter takes much longer to deliver some packets than others.</div>
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<div>
Lecture No. 23</div>
<div>
INTERNETWORKING: CONCEPTS,</div>
<div>
ARCHITECTURE AND PROTOCOLS</div>
<div>
THE MOTIVATION FOR INTERNETWORKING:</div>
<div>
There is no single networking technology that is best for all needs. A large</div>
<div>
organization with diverse networking requirements needs multiple physical networks. If</div>
<div>
the organization chooses the type of network that is best for each task, the organization</div>
<div>
will need several types of networks.</div>
<div>
The interconnection of two or more networks, usually local area networks so that</div>
<div>
data can pass between hosts on the different networks as though they were one network,</div>
<div>
this requires some kind of Router or Gateway, which led to the motivation for</div>
<div>
internetworking.</div>
<div>
THE CONCEPT OF UNIVERSAL SERVICE:</div>
<div>
The chief problems with multiple networks are as follows:</div>
<div>
• A computer attached to a given network can only communicate with other</div>
<div>
computers attached to the same network.</div>
<div>
• In the 1970s large organizations began to acquire multiple networks. Each</div>
<div>
network in the organization formed island. Employees needed to choose a</div>
<div>
computer appropriate for each task. So they needed multiple screens, keyboards</div>
<div>
and computers.</div>
<div>
UNIVERSAL SERVICES:</div>
<div>
A communication system that supplies universal services allows arbitrary pairs of</div>
<div>
computers to communicate.</div>
<div>
Universal service is desirable because it increases individual productivity.</div>
<div>
UNIVERSAL SERVICES IN A HETEROGENEOUS WORLD:</div>
<div>
Although universal service is highly desirable incompatibilities among network</div>
<div>
hardware and physical addressing prevent an organization from building a bridged</div>
<div>
network that includes arbitrary technologies.</div>
<div>
Extension techniques such as bridging cannot be used with heterogeneous</div>
<div>
network because of incompatible packet formats.</div>
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<div>
INTERNETWORKING:</div>
<div>
Despite the incompatibilities among networks, researchers have devised a scheme</div>
<div>
that provides universal service among heterogeneous networks called ‘internetworking’.</div>
<div>
It uses both hardware and software.</div>
<div>
PHYSICAL NETWORK CONNECTION WITH ROUTERS:</div>
<div>
A router is a special purpose system dedicated to the task of interconnecting</div>
<div>
networks. A router can interconnect networks that use different technologies including</div>
<div>
different media, physical addressing schemes or frame formats. A router connecting two</div>
<div>
physical networks is shown in the figure below.</div>
<div>
Figure 23.1</div>
<div>
INTERNET ARCHITECTURE:</div>
<div>
Organization seldom uses a single router to connect its entire network for two reasons.</div>
<div>
• Because the router must forward each packet, the processor in a given router is</div>
<div>
insufficient to handle the traffic.</div>
<div>
• Redundancy improved Internet reliability.</div>
<div>
An Internet consists of a set of networks interconnected by routers.</div>
<div>
The Internet scheme allows each organization to choose the number and type of network,</div>
<div>
the number of routers to use to interconnect them, and the exact interconnection</div>
<div>
topology. Three routers connecting four networks in series is shown in the figure below.</div>
<div>
Figure 23.2</div>
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<div>
ACHIEVING UNIVERSAL SERVICES:</div>
<div>
The goal of internetworking is universal service across heterogeneous networks.</div>
<div>
To provide this service all computers and routers must agree to forward information from</div>
<div>
a source on one network to a specified destination. The task is complicated as frame</div>
<div>
formats and addressing schemes may differ. The key of achieving universal service is</div>
<div>
universal protocol software (TCP/IP).</div>
<div>
A virtual network is shown in the figure that TCP/IP software provides to users</div>
<div>
and applications.</div>
<div>
Figure 23.3</div>
<div>
LAYERING AND TCP/IP PROTOCOLS:</div>
<div>
TCP/IP protocols are organized into five conceptual layers.</div>
<div>
Although some layers of the TCP/IP reference model correspond to layers of the ISO</div>
<div>
reference model, the ISO layers scheme does not have a layer that corresponds to TCP/IP</div>
<div>
Internet Layer.</div>
<div>
TCP/IP reference model is shown in the figure below.</div>
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<div>
Figure 23.4</div>
<div>
LAYER 1:</div>
<div>
Corresponds to basic network hardware layer in OSI.</div>
<div>
LAYER 2:</div>
<div>
Specifies how to organize data in frames.</div>
<div>
LAYER 3:</div>
<div>
Specifies the format of packets sent across an Internet and forwards packets.</div>
<div>
LAYER 4:</div>
<div>
Specifies how to ensure reliable transfer.</div>
<div>
LAYER 5:</div>
<div>
Like 6 and 7 in OSI model, it specifies how one application uses an Internet.</div>
<div>
HOST COMPUTERS, ROUTERS AND PROTOCOL LAYERS:</div>
<div>
TCP/IP defines the term host computer to refer to any computer system that</div>
<div>
connects to an Internet and runs applications. A TCP/IP protocol makes it possible for</div>
<div>
any pair of hosts to communicate despite hardware differences.</div>
<div>
Both host and routers need TCP/IP protocol software but routers do not need layer</div>
<div>
5 protocols for applications, as they do not run applications.</div>
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<div>
Lecture No. 24</div>
<div>
IP: INTERNET PROTOCOL ADDRESSES</div>
<div>
ADDRESSES FOR THE VIRTUAL INTERNET:</div>
<div>
To provide uniform addressing in Internet, protocol software defines an abstract</div>
<div>
addressing scheme that assigns each host a unique protocol address.</div>
<div>
Users, application programs and higher layers of protocol software use the</div>
<div>
abstract protocol software addresses to communicate.</div>
<div>
THE IP ADDRESSING SCHEME:</div>
<div>
An Internet address (IP address) is a unique 32-bit binary number assigned to a</div>
<div>
host and used for all communication with the host. Each packet sent across an Internet</div>
<div>
contains the 32-bit IP address of the sender (source) as well as the intended recipient</div>
<div>
(destination).</div>
<div>
THE IP ADDRESS HIERARCHY:</div>
<div>
Each 32-bit IP address is divided into two parts:</div>
<div>
PREFIX:</div>
<div>
It identifies the physical network to which the computers are attached.</div>
<div>
SUFFIX:</div>
<div>
It identifies an individual computer on the network.</div>
<div>
The physical network in an Internet is assigned a unique value known as a</div>
<div>
network number. No two networks can be assigned the same network number and no two</div>
<div>
computers on the same network can be assigned the same suffix. A suffix value can be</div>
<div>
used on more than one network.</div>
<div>
The IP address hierarchy guarantees two important principles:</div>
<div>
1. Each computer is assigned a unique address.</div>
<div>
2. Although network number assignment must be coordinated globally, suffixes can</div>
<div>
be assigned locally.</div>
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<div>
ORIGINAL CLASSES OF IP ADDRESSES:</div>
<div>
The original IP address scheme divides host addresses into three primary classes.</div>
<div>
The class of an address determines the boundary between the network prefix and suffix.</div>
<div>
The original classes of IP addresses are shown in the figure below.</div>
<div>
Figure: 24.1</div>
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<div>
Lecture No. 25</div>
<div>
INTERNET PROTOCOL ADDRESS NOTATIONS</div>
<div>
COMPUTING THE CLASS OF AN ADDRESS:</div>
<div>
Whenever it handles a packet, IP software needs to separate the destination</div>
<div>
address into a prefix and suffix. Classful IP addresses are self-identifying because the</div>
<div>
class of the address can be computed from the address itself. The table shows in the</div>
<div>
figure below how the class of address can be computed.</div>
<div>
Figure: 25.1</div>
<div>
DOTTED DECIMAL NOTATION:</div>
<div>
Dotted decimal notation is a syntactic form the IP software uses to express 32-bit</div>
<div>
binary values when interacting with humans. Dotted decimal represents each octet in</div>
<div>
decimal and uses a dot to separate octets. This is shown in the figure below.</div>
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<div>
Figure 25.2</div>
<div>
CLASSES AND DOTTED DECIMAL NOTATION:</div>
<div>
The relationship between classes and dotted decimal notation is given as follows.</div>
<div>
In class A the three octets correspond to a host suffix.</div>
<div>
In class B the last two octets are the host octets.</div>
<div>
Class C has only one octet to represent the host.</div>
<div>
The range of decimal values found in the first octet of each address class is given below</div>
<div>
in the figure.</div>
<div>
`</div>
<div>
Figure: 25.3</div>
<div>
DIVISION OF THE ADDRESS SPACE:</div>
<div>
The IP class scheme does not divide the 32-bit address space into equal size class</div>
<div>
and the classes do not contain the same number of networks.</div>
<div>
A prefix of n bits allows 2n unique network number, while a suffix of n bits</div>
<div>
allows 2n host numbers to be assigned on a given network. This is shown in the table</div>
<div>
below.</div>
<div>
Figure 25.4</div>
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<div>
AUTHORITY FOR ADDRESSES:</div>
<div>
Throughout the Internet, each network prefix is unique. Networks obtain their</div>
<div>
network numbers from their Internet service provider (ISP). The Internet service</div>
<div>
providers coordinate with the Internet assigned number authority to obtain their network</div>
<div>
numbers.</div>
<div>
CLASSFUL ADDRESSING EXAMPLE:</div>
<div>
Here we have a private TCP/IP network, which consists of four physical networks</div>
<div>
as shown in the figure below.</div>
<div>
The first step is to assign IP addresses in which usually class C addresses are</div>
<div>
assigned. Network administrator computes the ultimate size of each physical network and</div>
<div>
assigns a prefix.</div>
<div>
Figure: 25.5</div>
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<div>
Lecture No. 26</div>
<div>
IP SUBNETING</div>
<div>
SUBNETS AND CLASSLESS ADDRESSING:</div>
<div>
As the Internet grew, the original Classful addressing scheme became a limitation.</div>
<div>
The IP address space was being exhausted because all networks had to choose one of</div>
<div>
three possible sizes. Many addresses were unused.</div>
<div>
Two new mechanisms were invented to overcome the limitations, which are as</div>
<div>
follows:</div>
<div>
• Subnet addressing</div>
<div>
• Classless addressing</div>
<div>
Instead of having three distinct address classes, allow the division between prefix and</div>
<div>
suffix to occur on an arbitrary boundary. The classless addressing scheme solves the</div>
<div>
problem by allowing an ISP to assign a prefix that is, 28 bits long (allowing the host to</div>
<div>
have up to 14 hosts).</div>
<div>
SUBNET/ADDRESS MASK:</div>
<div>
How can an IP address be divided at an arbitrary boundary? To use a classless or</div>
<div>
subnet address, table inside hosts and routers that contain address must keep two pieces</div>
<div>
of information with each address: the 32-bit address itself and another 32-bit value that</div>
<div>
specifies the boundary that is known as the Address Mask or Subnet Mask.</div>
<div>
Suppose</div>
<div>
D = Destination Address</div>
<div>
(A, M)= (32-bit IP Address, 32-bit Address Mask)</div>
<div>
A = = (D & M)</div>
<div>
Now as an example consider a 32-bit mask:</div>
<div>
11111111 11111111 00000000 00000000</div>
<div>
Which can be denoted in dotted decimal as 255.255.0.0.</div>
<div>
Consider a network prefix:</div>
<div>
10000000 00001010 00000000 00000000</div>
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<div>
Which can be denoted in dotted decimal value as 128.10.0.0.</div>
<div>
Consider a destination address: 128.10.2.3</div>
<div>
That has Binary equivalent as:</div>
<div>
10000000 00001010 00000010 00000011</div>
<div>
A logical ‘and’ between D and M produces the binary result as:</div>
<div>
10000000 00001010 00000000 00000000</div>
<div>
Which is equal to prefix 128.10.0.0.</div>
<div>
CIDR NOTATION:</div>
<div>
Inside a computer, each address mask is stored as a 32-bit value. When we enter a</div>
<div>
prefix and an address mask they use a modified form of dotted decimal addressing called</div>
<div>
CIDR addressing, which is known as CIDR Notation.</div>
<div>
As an example how CIDR adds flexibility, suppose a single class B prefix (e.g.</div>
<div>
128.211.0.0) i.e. 216 host addresses 16-bit CIDR mask denoted as:</div>
<div>
128.211.0.0/16</div>
<div>
That is, by making CIDR mask corresponds exactly to the old Classful</div>
<div>
interpretation. It will be fine if 216 hosts are attached. If it does have two customers with</div>
<div>
only twelve computers each, the ISP can use CIDR to partition the address into three</div>
<div>
pieces.</div>
<div>
• Two of them each big enough for one of two customers.</div>
<div>
• Remainder available for future customers.</div>
<div>
For example one customer can be assigned 128.211.0.16/28 and the other</div>
<div>
customer can be assigned 128.211.0.32/28. Both customers have same mask size, the</div>
<div>
prefix differs i.e. each customer has a unique prefix.</div>
<div>
CIDR HOST ADDRESSES:</div>
<div>
The example below in the figure shows the CIDR host addresses:</div>
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<div>
Figure: 26.1</div>
<div>
SUMMARY OF SPECIAL IP ADDRESSES:</div>
<div>
The table below shows a summary of special IP addresses.</div>
<div>
Figure 26.2</div>
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<div>
Lecture No. 27</div>
<div>
ADDRESS REOLUTION PROTOCOL (ARP)</div>
<div>
PROTOCOL ADDRESSES AND PACKET DELIVERY:</div>
<div>
Protocol addresses are abstractions provided by software. Physical network</div>
<div>
hardware does not know how to locate a computer from it protocol address. The protocol</div>
<div>
address of the next hop must be translated to an equivalent hardware address before a</div>
<div>
packet can be sent.</div>
<div>
ADDRESS RESOLUTION:</div>
<div>
Mapping between a protocol address and a hardware address is called Address</div>
<div>
Resolution. A host or router uses address resolution when it needs to send a packet to</div>
<div>
another computer on the same physical network. A computer never resolves the address</div>
<div>
of a computer that attaches to a remote network.</div>
<div>
In the figure below a simple Internet with routers R1 & R2 connecting three</div>
<div>
physical networks is shown each network has two host computers attached.</div>
<div>
Figure 27.1</div>
<div>
In the figure, A resolves protocol address for B for protocol messages from an</div>
<div>
application on A sent to an application on B. A does not resolve a protocol address for F.</div>
<div>
Through the Internet layer, A delivers to F by routing through R1 and R2. A resolves R1</div>
<div>
hardware address.</div>
<div>
Network layer on A passes packet containing destination protocol address F for</div>
<div>
delivery to R1.</div>
<div>
ADDRESS RESOLUTION TECHNIQUES:</div>
<div>
Address resolution algorithms can be grouped into three basic categories:</div>
<div>
• Table lookup</div>
<div>
• Closed-form computation</div>
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<div>
• Message Exchange</div>
<div>
1. TABLE LOOKUP:</div>
<div>
In Table Lookup, binding or mapping is stored in a table in memory, which the software</div>
<div>
searches when it needs to resolve an address.</div>
<div>
2. CLOSED-FORM COMPUTATION:</div>
<div>
In Closed-form computation, the protocol address assigned to a computer is chosen</div>
<div>
carefully so that computer’s hardware address can be computed from the protocol address</div>
<div>
using basic Boolean and arithmetic operations.</div>
<div>
3. MESSAGE EXCHANGE:</div>
<div>
In Message Exchange, Computers exchange messages across a network to resolve an</div>
<div>
address. One computer sends a message that requests an address binding (translation) and</div>
<div>
another computer sends a reply that contains the requested information.</div>
<div>
Now we discuss in some detail these three categories.</div>
<div>
ADDRESS RESOLUTION WITH TABLE LOOKUP:</div>
<div>
Resolution requires data structure that contains information about address binding. A</div>
<div>
separate address-binding table is used for each physical network. The chief advantage of</div>
<div>
the table lookup approach is generality; a table can store the address bindings for an</div>
<div>
arbitrary set of computers.</div>
<div>
For less than a dozen hosts, a sequential search can suffice. For large networks the</div>
<div>
sequential approach uses too much CPU time. In the table below the hardware addresses</div>
<div>
for their corresponding IP addresses are given.</div>
<div>
Figure 27.2</div>
<div>
There are two standard implementations to improve computational efficiency:</div>
<div>
• Hashing</div>
<div>
• Direct indexing</div>
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<div>
HASHING:</div>
<div>
Hashing is the transformation of a string of characters into a usually</div>
<div>
shorter fixed-length value or a key that represents the original string. Hashing is used to</div>
<div>
index and retrieve items in a database because it is faster to find the item using the shorter</div>
<div>
hashed key than to find it using the original value. It is also used in many encryption</div>
<div>
algorithms.</div>
<div>
DIRECT INDEXING:</div>
<div>
It is less generally known technique. It is possible only is cases where protocols</div>
<div>
address are assigned from a compact range. In the figure below an example of direct</div>
<div>
lookup for a class C network is shown.</div>
<div>
Figure 27.3</div>
<div>
ADDRESS RESOLUTION WITH CLOSED-FORM</div>
<div>
COMPUTATION:</div>
<div>
For networks use configurable addressing, it is possible to choose an address that</div>
<div>
makes closed-form address resolution possible.</div>
<div>
A re-solver is used to compute a mathematical function that maps an IP address to a</div>
<div>
hardware address.</div>
<div>
When a computer connects to a network that uses configurable address, the local</div>
<div>
network administrator must choose a hardware address as well as an IP address. The two</div>
<div>
values can be chosen to make address resolution trivial. Let’s consider an example.</div>
<div>
EXAMPLE:</div>
<div>
Suppose a configurable network number:</div>
<div>
220.123.5.0/24</div>
<div>
The IP address of first host = 220.123.5.1</div>
<div>
Hardware Address = 1</div>
<div>
The IP address of second host = 220.123.5.2</div>
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Hardware Address = 2</div>
<div>
The IP address of router = 220.123.5.101</div>
<div>
Hardware Address = 101</div>
<div>
A simple Boolean ‘and’ operation can compute the computer’s hardware address.</div>
<div>
Hardware Address = ip_address & 0xff</div>
<div>
ADDRESS RESOLUTION WITH MESSAGE EXCHANGE:</div>
<div>
An alternative to local computations is a distributed approach. A computer that</div>
<div>
needs to resolve an address sends a message across a network and receives a reply. The</div>
<div>
message carries a request that species the protocol address and reply carries the</div>
<div>
corresponding hardware address.</div>
<div>
In this category there are two possible designs:</div>
<div>
• Centralized</div>
<div>
• Distributed</div>
<div>
CENTRALIZED:</div>
<div>
A network includes one or more servers that are assigned the task of answering</div>
<div>
address resolution requests. It has an advantage that resolution is easier to configure,</div>
<div>
manage and control.</div>
<div>
DISTRIBUTED:</div>
<div>
Each computer on the network participates in address resolution by agreeing to</div>
<div>
answer resolution request for its address. It also has an advantage that address resolution</div>
<div>
servers can become a bottleneck and reduce cost.</div>
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<div>
Lecture No. 28</div>
<div>
ARP MESSAGE FORMAT</div>
<div>
ADDRESS RESOLUTION SUMMARY:</div>
<div>
It is shown in the figure below, in which T stands for Table lookup, C for Closedform</div>
<div>
Computation and D for Data Exchange.</div>
<div>
Figure 28.1</div>
<div>
ADDRESS RESOLUTION PROTOCOL:</div>
<div>
TCP/IP can use any of the three address resolution methods depending on the</div>
<div>
addressing scheme used by the underlying hardware. To guarantee that all computers</div>
<div>
agree on the exact format and meaning of message used to resolve addresses. The TCP/IP</div>
<div>
protocol suite includes an Address Resolution Protocol (ARP).</div>
<div>
The ARP standard defines two basic message types:</div>
<div>
• Request</div>
<div>
• Response</div>
<div>
REQUEST:</div>
<div>
This contains and IP address and requests the corresponding hardware address.</div>
<div>
RESPONSE:</div>
<div>
This contains both the IP address sent in the request and the hardware address.</div>
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<div>
ARP MESSAGE DELIVERY:</div>
<div>
ARP message delivery is shown in the figure below.</div>
<div>
Figure 28.2</div>
<div>
ARP MESSAGE FORMAT:</div>
<div>
Although the ARP message format is sufficiently general to allow arbitrary</div>
<div>
protocol and hardware addresses. ARP is almost always used to bind a 32-bit IP address</div>
<div>
to a 48-bit Ethernet address.</div>
<div>
ARP format is shown in the figure below:</div>
<div>
Figure 28.3</div>
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<div>
SENDING AN ARP MESSAGE:</div>
<div>
When one computer sends an ARP message to another the message travels inside</div>
<div>
the hardware frame. Technically, placing a message inside a frame for transport is called</div>
<div>
encapsulation as shown in the figure below.</div>
<div>
Figure 28.4</div>
<div>
IDENTIFYING ARP RESPONSES:</div>
<div>
Let’s find out how a computer knows whether an incoming frame contains an</div>
<div>
ARP message. The type field in the frame header specifies that the frame contain an ARP</div>
<div>
message. The Ethernet standard species that the type field in an Ethernet frame carrying</div>
<div>
an ARP message must contain the hexadecimal value 0 x 806, as shown in the figure</div>
<div>
below.</div>
<div>
Figure 28.5</div>
<div>
CASHING ARP RESPONSES:</div>
<div>
Although message exchange can be used to bind addresses, sending a request for</div>
<div>
each binding is hopelessly inefficient. To reduce network traffic, ARP software extracts</div>
<div>
and saves the information from a response so that it can be used for subsequent packets.</div>
<div>
ARP manages the Table as a cache short-term storage.</div>
<div>
PROCESSING AN INCOMING ARP MESSAGE:</div>
<div>
When an ARP message arrives, the protocol specifies that the receiver must</div>
<div>
perform two basic steps.</div>
<div>
First the receiver extracts the sender’s addresses binding and checks to see if</div>
<div>
It is present in the cache. If not, it updates the cache.</div>
<div>
The receiver examines the operation field of the message to determine whether</div>
<div>
the message is a request or a response. If the message is a request, the receiver compares</div>
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<div>
the field TARGET PADDR with the local protocol address. If the two are identical, the</div>
<div>
computer is the target of the request and must send an ARP response.</div>
<div>
LAYERING, ADDRESS RESOLUTION AND PROTOCOL</div>
<div>
ADDRESSES:</div>
<div>
Address resolution (ARP) is a network interface layer function. Protocol</div>
<div>
addresses are used in all higher layers. Address resolution software hides ugly details and</div>
<div>
allows generality in upper layers. This is shown in the figure below.</div>
<div>
Figure 28.6</div>
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<div>
Lecture No. 29</div>
<div>
IP DATAGRAMS AND DATAGRAM FORWARDING</div>
<div>
CONNECTIONLESS SERVICE:</div>
<div>
End-to-end delivery service is connection less. The main features of</div>
<div>
connectionless service are as follows:</div>
<div>
It includes extension of LAN abstraction. It has universal addressing and the data</div>
<div>
is delivered in packets (frames), each with a header. It combines collection of physical</div>
<div>
networks into a single virtual network.</div>
<div>
Transport protocols use this connectionless service to provide:</div>
<div>
• Connectionless data delivery (UDP)</div>
<div>
• Connection-oriented data delivery (TCP)</div>
<div>
VIRTUAL PACKETS:</div>
<div>
These packets serve same purpose in Internet as frames on LAN. Each packet has</div>
<div>
a header. Routers, which are formally gateways, forward packets between physical</div>
<div>
networks.</div>
<div>
These packets have a uniform hardware-independent format. They include header</div>
<div>
and data and can’t use format from any particular hardware. They are encapsulated in</div>
<div>
hardware frames from delivery across each physical network.</div>
<div>
IP DATAGRAM FORMAT:</div>
<div>
Formally, the unit of IP data delivery is called a Datagram. It includes header area</div>
<div>
and data area as shown in the figure below.</div>
<div>
Figure 29.1</div>
<div>
IP DATAGRAM SIZE:</div>
<div>
Datagrams can have different sizes i.e.</div>
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<div>
Header area is usually fixed (20 octets) but can have options. Data area can contain</div>
<div>
between 1 octet and 65.535 octets (216-1).</div>
<div>
Usually, data area is much larger than header.</div>
<div>
FORWARDING DATAGRAMS:</div>
<div>
Header contains all information needed to deliver datagram to the destination</div>
<div>
computer. It contains:</div>
<div>
• Destination address</div>
<div>
• Source address</div>
<div>
• Identifier</div>
<div>
• Other delivery information</div>
<div>
Router examines header of each datagram and forwards datagram along path to</div>
<div>
destination.</div>
<div>
ROUTING TABLE:</div>
<div>
For efficiency, information about forwarding is stored in a routing table, which is</div>
<div>
initialized at system initialization and must be updated as network topology changes.</div>
<div>
The routing table contains list of destination networks and next hop for each destination.</div>
<div>
An example routing table is shown in the figure below.</div>
<div>
Figure 29.2</div>
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<div>
ROUTING TABLES AND ADDRESS MASKS:</div>
<div>
In practice, additional information is kept in routing table. Destination is stored as</div>
<div>
network address. Next hop is stored as IP address of router. Address mask defines how</div>
<div>
many bits of address are in prefix. Prefix defines how much of address used to identify</div>
<div>
network.</div>
<div>
For example, class A mask is 255.0.0.0 which is used for subnetting. A routing</div>
<div>
table with address masks is shown in the figure below:</div>
<div>
Figure 29.3</div>
<div>
ADDRESS MASKS:</div>
<div>
To identify destination, network apply address mask to destination address and</div>
<div>
compare to network address in routing table. It can use Boolean ‘and’ to compute the ith</div>
<div>
entry in the table.</div>
<div>
i.e.</div>
<div>
if ((Mask[i] & D) == Dest[i] ) forward to NextHop[i]</div>
<div>
FORWARDING, DESTINATION ADDRESS AND NEXT-HOP:</div>
<div>
Destination address in IP datagram is always ultimate destination. Router looks up</div>
<div>
next-hop address and forwards datagram. Network interface layer takes two parameters:</div>
<div>
• IP datagram</div>
<div>
• Next-hop address</div>
<div>
Next-hop address never appears in IP datagram.</div>
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<div>
BEST-EFFORT DELIVERY:</div>
<div>
IP provides service equivalent to LAN. It does not guarantee to prevent duplicate</div>
<div>
datagrams, delayed or out-of-order delivery, corruption of data and datagram loss.</div>
<div>
Transport layer provides reliable delivery. Network layer – IP – can detect and</div>
<div>
report errors without actually fixing them. It focuses on datagram delivery. Application</div>
<div>
layer is not interested in differentiating among delivery problems at intermediate routers.</div>
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<div>
Lecture No. 30</div>
<div>
IP ENCAPSULATION, FRAGMENTATION AND</div>
<div>
REASSEMBLY</div>
<div>
It is shown in the figure below:</div>
<div>
Figure 30.1</div>
<div>
In the figure:</div>
<div>
VERS shows the version of IP.</div>
<div>
H.LEN shows the header length in units of 32-bits.</div>
<div>
SERVICE TYPE shows sender’s preference for low latency, high reliability that is</div>
<div>
rarely used.</div>
<div>
TOTAL LENGTH shows total octets in datagram.</div>
<div>
IDENT, FLAGS, FRAGMENT OFFSET show the values used with fragmentation.</div>
<div>
TTL shows time to live decremented in each router; datagram discarded when TTL = 0.</div>
<div>
TYPE shows type of protocol carried in datagram e.g., TCP, UDP.</div>
<div>
HEADER CHECKSUM shows 1’s complement of 1’s complement sum.</div>
<div>
SOURCE DIST IP ADDRESS shows IP addresses of original source and ultimate</div>
<div>
destination.</div>
<div>
IP DATAGRAM OPTIONS:</div>
<div>
Several options can be added to IP header, e.g., record route, source route and</div>
<div>
timestamp. Header with no options has H. LEN field value 5; data begins immediately</div>
<div>
after DESTINATION IP ADDRESS. Options are added between DESTINATION IP</div>
<div>
ADDRESS and data in multiples of 32 bits. Header with 96 bits of options has H. LEN</div>
<div>
field value 8.</div>
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<div>
DATAGRAM TRANSMISSION AND FRAMES:</div>
<div>
IP Internet layer has following tasks:</div>
<div>
• It constructs datagram, determines next hop and hands to network interface layer.</div>
<div>
Network interface layer has following tasks:</div>
<div>
• It binds next hop address to hardware address and prepares datagram for</div>
<div>
transmission. But hardware frame doesn’t understand IP how datagram is</div>
<div>
transmitted?</div>
<div>
ENCAPSULATION:</div>
<div>
Network interface layer encapsulates IP datagram as data area in hardware frame.</div>
<div>
Hardware ignores IP datagram format. Standards for encapsulation describe details.</div>
<div>
Standard defines data type for IP datagram, as well as others (e.g., ARP). Receiving</div>
<div>
protocol stack interprets data area based on frame type. The encapsulation process is</div>
<div>
shown in the figure below.</div>
<div>
Figure 30.2</div>
<div>
ENCAPSULATION ACROSS MULTIPLE HOPS:</div>
<div>
Each router in the path from the source to the destination un-encapsulates</div>
<div>
incoming datagram from frame, processes datagram and determines next hop and</div>
<div>
encapsulates datagram in outgoing frame. Datagram may be encapsulated in different</div>
<div>
hardware format at each hop. Datagram itself is (almost) unchanged as shown in the</div>
<div>
figure below.</div>
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<div>
Figure 30.3</div>
<div>
MTU:</div>
<div>
Every hardware technology specification includes the definition of the maximum</div>
<div>
size of the frame data area, which is called the Maximum Transmission Unit (MTU). Any</div>
<div>
datagram encapsulated in a hardware frame must be smaller than the MTU for that</div>
<div>
hardware.</div>
<div>
MTU AND HETEROGENEOUS NETWORKS:</div>
<div>
An Internet may have networks with different MTUs as shown in the figure</div>
<div>
below. Suppose downstream network has smaller MTU than local network.</div>
<div>
Figure 30.4</div>
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<div>
FRAGMENTATION:</div>
<div>
One technique is to limit datagram size to smallest MTU of any network. IP uses</div>
<div>
fragmentation i.e. datagrams can be split into pieces to fit in network with small MTU.</div>
<div>
Router detects datagram larger than network MTU and then it splits into pieces</div>
<div>
and each piece is smaller than outbound network MTU.</div>
<div>
Each fragment is an independent datagram. It includes all header fields. Bit in</div>
<div>
header indicates that the datagram is a fragment. Other fields have information for</div>
<div>
reconstructing original datagram. Fragment offset gives original location of fragment.</div>
<div>
Router has local MTU to computer size of each fragment. It puts part of data from</div>
<div>
original datagram in each fragment and puts other information into header. The</div>
<div>
fragmentation process is shown in the figure below.</div>
<div>
Figure 30.5</div>
<div>
DATAGRAM REASSEMBLY:</div>
<div>
Reconstruction of original datagram is called reassembly. Ultimate destination</div>
<div>
performs reassembly as shown below.</div>
<div>
Figure 30.6</div>
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<div>
Fragments may arrive out of order. Header bit identifies fragments containing end</div>
<div>
of data from original datagram. In the figure 30.5 fragment 3 is identified as last</div>
<div>
fragment.</div>
<div>
FRAGMENT IDENTIFICATION:</div>
<div>
Let’s see how fragments are associated with original datagram. IDENT field in</div>
<div>
each fragment matches IDENT field in original datagram. Fragments from different</div>
<div>
datagrams can arrive out of order and still be sorted out.</div>
<div>
FRAGMENT LOSS:</div>
<div>
IP may drop fragment because destination drops entire original datagram.</div>
<div>
Destination sets timer with each fragment to identify lost fragment. If timer expires</div>
<div>
before all fragments arrive, fragment is assumed lost and datagram is dropped. Source</div>
<div>
(application layer protocol) is assumed to retransmit.</div>
<div>
FRAGMENTING A FRAGMENT:</div>
<div>
Fragment may encounter subsequent network with even smaller MTU. Router</div>
<div>
fragments the fragment to fit. Resulting sub-fragments look just like original fragments</div>
<div>
(except for size). There is no need to reassemble hierarchically as sub-fragments include</div>
<div>
position in original datagram.</div>
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<div>
Lecture No. 31</div>
<div>
THE FUTURE IP (IPV6)</div>
<div>
INTRODUCTION:</div>
<div>
The current version of IP- Version 4 (IPV4) is 20 years old. IPV4 has shown</div>
<div>
remarkable ability to move to new technologies. IEFT has proposed entirely new version</div>
<div>
to address some specific problems.</div>
<div>
SUCCESS OF IP:</div>
<div>
IP has accommodated dramatic changes since original design. But basic principles</div>
<div>
are still appropriate today. There are many new types of hardware.</div>
<div>
SCALING:</div>
<div>
Scale is also dramatically changed. Size from a few tens to a few tens of millions</div>
<div>
of computers has been revolutionized. Speed has increased from 56Kbps to 1Gbps. Also</div>
<div>
there is an increased frame size in hardware.</div>
<div>
MOTIVATION FOR CHANGE:</div>
<div>
One of the parameters, which motivated IP for change is address space. The 32-</div>
<div>
bit address space allows for over a million networks.</div>
<div>
But most networks are class C and too small for many organizations.</div>
<div>
214 class B network addresses already almost exhausted (and exhaustion was first</div>
<div>
predicted to occur, a couple of years ago).</div>
<div>
The second parameter is type of service, the IP provides.</div>
<div>
Different applications have different requirements for delivery reliability and speed.</div>
<div>
Current IP has type of service that is not often implemented. Another factor for the</div>
<div>
motivation for change is multicast.</div>
<div>
NAME AND VERSION NUMBER:</div>
<div>
A preliminary version of IP was called IP- Next Generation (IPng). There were</div>
<div>
several proposals and all called IPng. One name was selected and it used next available</div>
<div>
version number i.e. 6. The result is IP version 6 (IPV6).</div>
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<div>
NEW FEATURES:</div>
<div>
The new features of IPV6 are as follows:</div>
<div>
• IPV6 addresses are 128 bits.</div>
<div>
• Header format is entirely different.</div>
<div>
• Additional information is stored in optional extension headers, followed by data.</div>
<div>
• Flow label and quality of service allows audio and video applications to establish</div>
<div>
appropriate connections.</div>
<div>
• New features can be added more easily. So it is extensible.</div>
<div>
IPV6 DATAGRAM FORMAT:</div>
<div>
It is shown in the figure below:</div>
<div>
Figure: 31.1</div>
<div>
IPV6 BASE HEADER FORMAT:</div>
<div>
It contains less information than IPV4 header. Next header points to first</div>
<div>
extension header. Flow label is partitioned into a TRAFFIC CLASS field and a separate</div>
<div>
FLOW LABEL field used to identify a specific path thorough the network.</div>
<div>
Routers use flow label to forward datagrams along prearranged path.</div>
<div>
It is shown in the figure below:</div>
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<div>
Figure 31.2</div>
<div>
IPV6 NEXT HEADER:</div>
<div>
It is shown in the figure below:</div>
<div>
Figure 31.3</div>
<div>
PARSING IPv6 HEADERS:</div>
<div>
Base header is fixed size i.e. 40 octets. NEXT HEADER field in the base header</div>
<div>
defines type of header and it appears at end of fixed-size base header. Some extension</div>
<div>
headers are variable sized. NEXT HEADER field in extension header defines type.</div>
<div>
HEADER LEN field gives size of extension header as shown in the figure below:</div>
<div>
Figure 31.4</div>
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<div>
Lecture No. 32</div>
<div>
IPv6 AND AN ERROR REPORTING MECHANISM</div>
<div>
FRAGMENTATION:</div>
<div>
Fragmentation information is kept in separate extension header. Each fragment</div>
<div>
has base header and (inserted) fragmentation header. Entire datagram including original</div>
<div>
header may be fragmented. This process is shown in the figure below.</div>
<div>
Figure 32.1</div>
<div>
FRAGMENTATION AND PATH MTU:</div>
<div>
IPv6 source (not intermediate routers) is responsible for fragmentation. Routers</div>
<div>
simply drop datagrams larger than network MTU (Maximum Transmission Unit). So</div>
<div>
source must fragment datagram to reach destination.</div>
<div>
Source determines path MTU. The smallest MTU on any network between source</div>
<div>
and destination and it fragments datagram to fit within that MTU.</div>
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<div>
The process of learning the path MTU is known as path MTU discovery. Path</div>
<div>
MTU discovery is used. Source sends probe message of various sizes until destination</div>
<div>
reached. It must be dynamic i.e. path may change during transmission of datagrams.</div>
<div>
USE OF MULTIPLE HEADERS:</div>
<div>
It has following advantages:</div>
<div>
• Efficiency: Header is only as large as necessary.</div>
<div>
• Flexibility: it can add new headers for new features.</div>
<div>
• Incremental development: It can add processing for new features to testbed,</div>
<div>
other routers will skip those headers.</div>
<div>
IPv6 ADDRESSING:</div>
<div>
IPv6 uses 128-bit addresses. A 128-bit address includes network prefix</div>
<div>
and host suffix. An advantage of IPv6 addressing is that it has no address classes i.e.</div>
<div>
prefix/suffix boundary can fall anywhere.</div>
<div>
Following are special types of addresses, IPv6 uses:</div>
<div>
Unicast: It is used for single destination computer.</div>
<div>
Multicast: It is used for multiple destinations; possibly not at same site.</div>
<div>
Cluster: This type of address is used for collection of computers with same prefix,</div>
<div>
datagram is delivered to one out of cluster.</div>
<div>
IPv6 ADDRESS NOTATION:</div>
<div>
128-bit addresses unwidely in dotted decimal; requires 16 numbers:</div>
<div>
105.220.136.100.255.255.255.255.0.0.18.128.140.10.255.255</div>
<div>
Groups of 16-bit numbers in hex separated by colons – colon hexadecimal (or colon hex).</div>
<div>
69DC: 8864:FFFF: FFFF: 0:1280:8C0A:FFFF</div>
<div>
Zero-compression – series of zeroes indicated by two colons</div>
<div>
FF0C: 0:0:0:0:0:0:B1</div>
<div>
FF0C::B1</div>
<div>
IPv6 address with 96 leading zeros is interpreted to hold an IPv4 address.</div>
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<div>
AN ERROR REPORTING MECHANISM (ICMP)</div>
<div>
INTRODUCTION:</div>
<div>
IP provides best-effort delivery. Delivery problems can be ignored; datagrams can</div>
<div>
be ‘dropped on the floor’. Internet Control Message Protocol (ICMP) provides errorreporting</div>
<div>
mechanism.</div>
<div>
BEST-EFFORT SEMANTICS AND ERROR DETECTION:</div>
<div>
Internet layer can detect a variety of errors: e.g.</div>
<div>
• Checksum (header only)</div>
<div>
• TTL expires</div>
<div>
• No route to destination network.</div>
<div>
• Can’t deliver to destination host (e.g., no ARP reply).</div>
<div>
Internet layer discards datagrams with problems. Some - for example, checksum</div>
<div>
error – can’t trigger error messages.</div>
<div>
INTERNET CONTROL MESSAGE PROTOCOL:</div>
<div>
Some errors can be reported. Router sends message back to source in datagram.</div>
<div>
Message contains information about problem. It is encapsulated in IP datagram.</div>
<div>
TYPES OF MESSAGES:</div>
<div>
Internet control Message Protocol (ICMP) defines error and informational</div>
<div>
messages. These are given as follows:</div>
<div>
1. ERROR MESSAGES:</div>
<div>
These are as follows:</div>
<div>
• Source quench</div>
<div>
• Time exceeded</div>
<div>
• Destination unreachable</div>
<div>
• Redirect</div>
<div>
• Fragmentation required</div>
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<div>
2. INFORMATIONAL MESSAGES:</div>
<div>
These are as follows:</div>
<div>
• Echo request/reply</div>
<div>
• Address mask request /reply</div>
<div>
• Router discovery</div>
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<div>
Lecture No. 33</div>
<div>
AN ERROR REPORTING MECHANISM (ICMP)</div>
<div>
ICMP MESSAGE TRANSPORT:</div>
<div>
ICMP message transport is acted upon by getting ICMP encapsulated in IP. This</div>
<div>
is shown in the figure below:</div>
<div>
Figure 32.2</div>
<div>
ICMP message is sent in response to incoming datagrams with problems. ICMP</div>
<div>
message is not sent for ICMP message.</div>
<div>
USING ICMP TO TEST REACHABILITY:</div>
<div>
ICMP can also be used to test different tools. An Internet host A, is reachable</div>
<div>
from another host B, if datagrams can be delivered from A to B. Ping program tests</div>
<div>
reachability. It sends datagram from B to A, that echoes back to B. it uses ICMP echo</div>
<div>
request and echo reply messages. Internet layer includes code to reply to incoming ICMP</div>
<div>
echo request messages.</div>
<div>
USING ICMP TO TRACE A ROUTE:</div>
<div>
List of all routers on path from A to B is called the route from A to B. The</div>
<div>
intermediate routers send ICMP time exceeded message to the source and destination</div>
<div>
sends an ICMP destination unreachable message to the source.</div>
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<div>
Tracert (Windows version) sends ICMP echo messages with increasing TTL.</div>
<div>
Router that decrements TTL to 0 sends ICMP time exceeded message, with router’s</div>
<div>
address as source address. First, with TTL 1, gets to first router, which discards and sends</div>
<div>
time exceeded message. Next, with TTL 2 gets through first router to second router. It</div>
<div>
continues until an ICMP echo reply message from destination is received.</div>
<div>
THE LAST ADDRESS PRINTED BY TRACE-ROUTE:</div>
<div>
There are two possibilities used to detect the destination.</div>
<div>
• Send and ICMP echo request, destination host will generate an ICMP echo reply.</div>
<div>
• Send a datagram to a non-existent application, destination host will generate an</div>
<div>
ICMP destination unreachable message.</div>
<div>
USING ICMP FOR PATH MTU:</div>
<div>
Fragmentation should be avoided. Source can configure outgoing datagrams to</div>
<div>
avoid fragmentation. Source determines path MTU- smallest network MTU on path from</div>
<div>
source to destination. Source probes path using IP datagrams with don’t fragment flag.</div>
<div>
Router responds with ICMP fragmentation required message. Source sends smaller</div>
<div>
probes until destination reached.</div>
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<div>
Lecture No. 34</div>
<div>
UDP: DATAGRAM TRANSPORT SERVICE</div>
<div>
TERMINOLOGY:</div>
<div>
IP:</div>
<div>
• Provides computer-to-computer communication.</div>
<div>
• Source and destination addresses are computers.</div>
<div>
• This is also called machine-to-machine communication.</div>
<div>
TRANSPORT PROTOCOLS:</div>
<div>
• Provide application-to-application communication.</div>
<div>
• Need extended addressing mechanisms to identify applications.</div>
<div>
• Are called end-to-end communication.</div>
<div>
INTRODUCTION:</div>
<div>
UDP is the first of the transport protocols in TCP/IP protocol suite. UDP protocol</div>
<div>
allows applications on the computers to send and receive datagrams. UDP has a packet</div>
<div>
format. It uses best-effort delivery service.</div>
<div>
THE NEED FOR TRANSPORT PROTOCOLS:</div>
<div>
Internet protocol can not distinguish between application programs running on the</div>
<div>
same computer. Fields in the IP datagram header refer to computers, not applications. A</div>
<div>
protocol that allows an application program to serve as the end point of communication is</div>
<div>
known as a transport protocol or an end-to-end protocol.</div>
<div>
THE USER DATAGRAM PROTOCOL (UDP):</div>
<div>
TCP/IP contains two transport protocols:</div>
<div>
• UDP</div>
<div>
• TCP</div>
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<div>
UDP:</div>
<div>
UDP is less complex and easier to understand. It does not provide the type of</div>
<div>
service a typical application expects.</div>
<div>
CHARACTERISTICS OF UDP:</div>
<div>
UDP has the following characteristics.</div>
<div>
• It is an end-to-end protocol. It provides application-to-application communication.</div>
<div>
• It provides connectionless service.</div>
<div>
• It is a Message-Oriented protocol.</div>
<div>
• It uses best-effort delivery service.</div>
<div>
• It follows arbitrary interaction.</div>
<div>
• It is operating system independent.</div>
<div>
THE CONNECTIONLESS PARADIGM:</div>
<div>
UDP does not need to pre-establish communication and also there is no need to</div>
<div>
terminate communication. UDP allows an application to delay long intervals between two</div>
<div>
messages. There are no Control Messages; only Data Messages. So it has very low</div>
<div>
overhead.</div>
<div>
MESSAGE-ORIENTED INTERFACE:</div>
<div>
UDP offers application programs a Message-Oriented Interface. It does not divide</div>
<div>
messages into packets for transmission and does not combine messages for delivery.</div>
<div>
Let’s discuss its advantages and disadvantages.</div>
<div>
ADVANTAGES:</div>
<div>
• Applications can depend on protocol to preserve data boundaries.</div>
<div>
DISADVANTAGES:</div>
<div>
• Each UDP message must fit into a single IP datagram.</div>
<div>
• It can result to an inefficient use of the underlying network.</div>
<div>
•</div>
<div>
UDP COMMUNICATION SEMANTICS:</div>
<div>
UDP uses IP for all delivery, that is, same best effort delivery as IP.</div>
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<div>
To use UDP, an application must either be immune to the problems or</div>
<div>
programmer must take additional steps to detect and correct problems.</div>
<div>
EXAMPLES:</div>
<div>
• Audio transmission</div>
<div>
• On-line shopping application</div>
<div>
ARBITRARY INTERACTION:</div>
<div>
UDP follows four types of interaction</div>
<div>
• 1-to-1: One application can communicate with one application.</div>
<div>
• 1-to-many: One application can communicate with many applications.</div>
<div>
• Many-to-1: Many applications can communication with one</div>
<div>
application.</div>
<div>
• Many-to-many: Many applications can communicate with many</div>
<div>
applications.</div>
<div>
SUPPORT FOR UNICAST, MULTICAST AND BROADCAST:</div>
<div>
UDP allows multicast 1-to-many interaction using multicast or a broadcast.</div>
<div>
Sender uses a broadcast address as the destination address to interact with many</div>
<div>
applications. It is especially useful for Ethernet networks.</div>
<div>
ENDPOINT IDENTIFICATION WITH PROTOCOL PORT</div>
<div>
NUMBERS:</div>
<div>
UDP identifies an application as an endpoint.</div>
<div>
Mechanism cannot be the same as of the operating system. No common mechanisms</div>
<div>
exist. There are multiple identifiers like protocol identifiers, job names and task</div>
<div>
identifiers.</div>
<div>
UDP defines a set of identifiers called ‘protocol ports.’</div>
<div>
It is independent of the underlying operating system. Each computer using UDP</div>
<div>
provides a mapping between the protocol port number and the program identifiers of its</div>
<div>
operating system.</div>
<div>
The address and protocol port specifications of an application define the type of</div>
<div>
communication. To engage in a 1-to-1 communication, the application specifies:</div>
<div>
• The local port number</div>
<div>
• Remote IP address</div>
<div>
• The remote port number</div>
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<div>
Lecture No. 35</div>
<div>
DATAGRAM FORMAT AND TCP: RELIABLE</div>
<div>
TRANSPORT SERVICE</div>
<div>
UDP DATAGRAM FORMAT:</div>
<div>
It is shown in the figure below:</div>
<div>
Figure 35.1</div>
<div>
UDP ENCAPSULATION:</div>
<div>
As shown in the figure below, UDP packet is encapsulated in IP datagram and the</div>
<div>
IP datagram is then encapsulated in the Frame.</div>
<div>
Figure 35.2</div>
<div>
TCP:</div>
<div>
INTRODUCTION:</div>
<div>
TCP is the major transport protocol in the TCP/IP suite. It uses unreliable</div>
<div>
datagram service offered by IP when sending data to another computer. It provides</div>
<div>
reliable data delivery service to applications.</div>
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<div>
THE NEED FOR RELIABLE TRANSPORT:</div>
<div>
Reliability is fundamental in a computer system. Software in the Internet must</div>
<div>
provide the same level of reliability as a computer system. Software must guarantee</div>
<div>
prompt and reliable communication without any loss, duplication, and change in the</div>
<div>
order.</div>
<div>
TRANSMISSION CONTROL PROTOCOL:</div>
<div>
Reliability is the responsibility of the Transport layer. In TCP/IP, TCP provides</div>
<div>
reliable transport service. Most Internet applications use TCP as no other protocol has</div>
<div>
proved to work better.</div>
<div>
SERVICE PROVIDED BY TCP:</div>
<div>
Following are the services provided by TCP:</div>
<div>
• Connection-oriented service</div>
<div>
• Point-to-point</div>
<div>
• Complete reliability</div>
<div>
• Full-duplex communication</div>
<div>
• Stream interface</div>
<div>
• Reliable connection startup</div>
<div>
• Graceful connection shutdown</div>
<div>
END-TO-END SERVICE AND DATAGRAMS:</div>
<div>
Applications can request a connection. TCP connections are called Virtual</div>
<div>
Connections. They are created by software only. Internet does not provide software or</div>
<div>
hardware support for the connections. TCP software modules on two computers create an</div>
<div>
illusion of a connection.</div>
<div>
TCP uses IP to carry messages. TCP message is encapsulated in IP datagram and</div>
<div>
sent to the destination. On the destination host, IP passes the contents to TCP. It is shown</div>
<div>
in the figure below.</div>
<div>
Figure 35.3</div>
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<div>
ACHIEVING RELIABILITY:</div>
<div>
The major problems in the reliable delivery are:</div>
<div>
• Unreliable delivery by the underlying communication system.</div>
<div>
• System reboots.</div>
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<div>
Lecture No. 36</div>
<div>
TCP: RELIABLE TRANSPORT SERVICE (Cont.)</div>
<div>
PACKET LOSS AND RETRANSMISSION:</div>
<div>
TCP achieves reliability by retransmission. An acknowledgement is used to verify</div>
<div>
that data has arrived successfully. If acknowledgement does not arrive, the previous data</div>
<div>
is retransmitted. This is shown in the figure below:</div>
<div>
Figure 36.1</div>
<div>
HOW LONG SHOULD TCP WAIT BEFORE RETRANSMITTING:</div>
<div>
The time for acknowledgement to arrive depends on:</div>
<div>
• Distance to destination</div>
<div>
• Current traffic conditions</div>
<div>
Multiple connections can be opened simultaneously. Traffic conditions change rapidly.</div>
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<div>
ADAPTIVE RETRANSMISSION:</div>
<div>
Setting a timer sounds so easy but the question is “what time interval?” If the time</div>
<div>
interval is too large, you are spending time waiting for something that is just not going to</div>
<div>
happen. If the time interval is too short, you will resend needlessly.</div>
<div>
So keep estimate of round trip time on each connection, and use current estimate</div>
<div>
to set transmission timer. This is known as ‘Adaptive Retransmission’. This is a key to</div>
<div>
TCP’s success.</div>
<div>
COMPARISON OF RETRANSMISSION TIMES:</div>
<div>
The figure shows a comparison of retransmission times. The network having short</div>
<div>
intervals has a short timeout and the network having large interval has large timeout.</div>
<div>
Figure 36.2</div>
<div>
BUFFER, FLOW CONTROL AND WINDOWS:</div>
<div>
TCP uses window mechanism to control the flow of data. The amount of buffer</div>
<div>
space available at any time is called the window and a notification that specifies the size</div>
<div>
is called the window advertisement.</div>
<div>
In the figure below a sequence of messages that illustrates TCP flow control when</div>
<div>
the maximum segment size is 1000 octets. A sender can transmit enough data to fill the</div>
<div>
currently advertised window.</div>
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<div>
Figure 36.3</div>
<div>
THREE WAY HANDSHAKES TO CLOSE A CONNECTION:</div>
<div>
The figure below shows a three-way handshake to close a connection.</div>
<div>
Acknowledgements sent in each direction are used to guarantee that all data has arrived</div>
<div>
before the connection is terminated.</div>
<div>
Figure 36.4</div>
<div>
THREE-WAY HANDSHAKE TO BEGIN A CONNECTION:</div>
<div>
Part of the 3-way handshake used to create a connection, requires each end to</div>
<div>
generate a random 32-bit sequence number. If an application attempts to establish a new</div>
<div>
TCP connection after a computer reboots, TCP chooses a new random number.</div>
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<div>
Lecture No. 37</div>
<div>
NETWORK ADDRESS TRANSLATION (NAT)</div>
<div>
CONGESTION CONTROL:</div>
<div>
The goal of congestion control is to avoid adding retransmissions to an already</div>
<div>
congested network. Reducing the window size quickly in response to the lost messages</div>
<div>
does it. It is assumed that loss is due to congestion.</div>
<div>
We have to resume carefully. Otherwise the network will swing wildly between</div>
<div>
congestion and under utilization.</div>
<div>
TCP SEGMENT FORMAT:</div>
<div>
It is shown in the figure below. TCP uses single format for all messages. TCP</div>
<div>
uses the term segment to refer to a message. Each message sent from TCP on one</div>
<div>
machine to TCP on another machine uses this format including data and</div>
<div>
acknowledgement.</div>
<div>
Figure 37.1</div>
<div>
NETWORK ADDRESS TRANSLATION:</div>
<div>
It is the extension of original addressing scheme and was motivated by exhaustion</div>
<div>
of IP address space. It allows multiple computers to share a single address. It requires</div>
<div>
device to perform packet translation.</div>
<div>
Its implementations are available e.g.,</div>
<div>
• Stand-alone hardware device</div>
<div>
• IP router with NAT functionality embedded</div>
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<div>
NAT DETAILS:</div>
<div>
Site that consists of more than one computer, obtains a single valid IP address. It</div>
<div>
assigns a private address to each computer and uses NAT box to connect to the Internet.</div>
<div>
NAT translates address in IP datagrams.</div>
<div>
ILLUSTRATION OF NAT:</div>
<div>
The figure illustrates the NAT functionality. When a computer in the site</div>
<div>
communicates to the internet, the NAT device, as shown in the figure below, translates its</div>
<div>
private address in the site to the global IP address and vice versa.</div>
<div>
Figure 37.2</div>
<div>
NAT EXAMPLE:</div>
<div>
For example, a site uses private network 10.0.0.0/8 internally.</div>
<div>
First computer is assigned 10.0.0.1, second computer is assigned 10.0.0.2 and so on…</div>
<div>
Site obtains a valid IP address (e.g. 128.210.24.6). Let’s assume that the</div>
<div>
computer 10.0.0.1 sends to 128.211.134.4 (another global IP address). NAT translates the</div>
<div>
IP source address of the outgoing datagram to the global IP address. NAT also translates</div>
<div>
the destination address of incoming datagram to the private site address. It is shown in the</div>
<div>
figure below.</div>
<div>
Figure 37.3</div>
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<div>
ILLUSTRATION OF NAT TRANSLATION:</div>
<div>
It is transparent to each end i.e. computer at site sends and receives datagrams</div>
<div>
normally and computer at Internet receives datagrams from NAT box.</div>
<div>
IMPLEMENTATION OF NAT:</div>
<div>
The figure below shows the implementation of NAT. We can see that the old and</div>
<div>
new values of IP source field and destination field are shown with their directions.</div>
<div>
Figure 37.4</div>
<div>
NAT device stores state information in table. The value is entered in the table</div>
<div>
when NAT box receives outgoing datagram from new</div>
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<div>
Lecture No. 38</div>
<div>
NETWORK ADDRESS TRANSLATION</div>
<div>
VARIANTS OF NAT:</div>
<div>
There are also some variants of NAT due to some of its drawbacks.</div>
<div>
The basic NAT simply changes IP addresses. But Network Address and Port</div>
<div>
Translation (NAPT) (which is another modified form of NAT) changes IP addresses and</div>
<div>
protocol port numbers too. It is the most popular form of NAT.</div>
<div>
Twice NAT is another variant of NAT. it is used with site that runs server. In this</div>
<div>
process NAT box is connected to Domain Name.</div>
<div>
NETWORK ADDRESS AND PORT TRANSLATION (NAPT):</div>
<div>
It is by far the most popular form of NAT that can change TCP or DP protocol</div>
<div>
port numbers as well as IP addresses.</div>
<div>
It allows multiple computers at site to communicate with single destination as</div>
<div>
well as multiple users on given computer to communicate with same destination.</div>
<div>
EXAMPLE NAPT TRANSLATION TABLE:</div>
<div>
An example NAPT translation table is shown in the figure below. We can see that</div>
<div>
not only the private addresses but also the port numbers are translated too.</div>
<div>
Figure 38.1</div>
<div>
Each entry in the table records protocol port numbers as well as IP address. The</div>
<div>
port numbers are reassigned to avoid conflicts.</div>
<div>
TCP SPLICING:</div>
<div>
A popular use of NAPT is TCP Splicing. It interconnects two independent TCP</div>
<div>
connections and performs segment rewriting. It is extremely efficient and avoids</div>
<div>
overhead of extracting data from one connection and sending to the other. It uses</div>
<div>
extended translation table.</div>
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<div>
TWICE NAT:</div>
<div>
Basic NAT does not work well for communication initiated from the Internet.</div>
<div>
Twice NAT allows a site to run servers. It requires the DNS to interact with the NAT</div>
<div>
device. Twice NAT fails if an application uses the IP addresses instead of Domain Name.</div>
<div>
CAT:</div>
<div>
Cable TV providers offering Internet services through Cable Modems propose it.</div>
<div>
It includes NAPT plus additional functionality. The additional functionality allows the</div>
<div>
cable operator to communicate with the CAT device, inspect values and control network</div>
<div>
access.</div>
<div>
NAT AT HOME:</div>
<div>
NAT is useful at a residence with Cable Modem or DSL connectivity as it allows</div>
<div>
the customer to have multiple computers at home without requiring an IP address for</div>
<div>
each of them. Instead a single IP address is used for all the computers. NAT software</div>
<div>
allows a PC to connect with the Internet and act as a NAT device at the same time.</div>
<div>
It is shown in the figure below where multiple computers are connected to the</div>
<div>
dedicated hardware device implementing NAT.</div>
<div>
Figure 38.2</div>
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<div>
Lecture No. 39</div>
<div>
IP ROUTING (Part-1)</div>
<div>
TERMINOLOGY:</div>
<div>
The forwarding and Routing are two different concepts and explained as follows:</div>
<div>
FORWARDING:</div>
<div>
It refers to datagram transfer. It is performed by host or router. It uses routing</div>
<div>
table.</div>
<div>
ROUTING:</div>
<div>
It refers to propagation of routing information. It is performed by routers. It</div>
<div>
inserts or changes values in routing table.</div>
<div>
TWO FORMS OF INTERNET ROUTING:</div>
<div>
STATIC ROUTING:</div>
<div>
It is one of the forms of Internet routing. In Static routing, the table is initialized</div>
<div>
when system boots and there is no further changes.</div>
<div>
DYNAMIC ROUTING:</div>
<div>
In dynamic routing the table is initialized when system boots. It includes routing</div>
<div>
software which learns routes and updates table. In this way continuous changes are</div>
<div>
possible due to routing software.</div>
<div>
STATIC ROUTING:</div>
<div>
It is used by most Internet hosts. The typical routing table has two entries as</div>
<div>
shown in the figure. For the local network it has direct delivery and for the</div>
<div>
communication to some other network it follows the nearest default route. The example is</div>
<div>
shown in the figure below where four hosts are attached to an Ethernet which connects to</div>
<div>
the rest of the internet through router R1.</div>
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<div>
DYNAMIC ROUTING:</div>
<div>
It is used by IP routers. It requires special software which continuously updates the</div>
<div>
routing information. Each router communicates with neighbors. It passes routing</div>
<div>
information and uses Route Propagation Protocol to exchange the information with other</div>
<div>
routers.</div>
<div>
EXAMPLE OF ROUTE PROPAGATION:</div>
<div>
In this example three networks are connected by two routers. In such a situation, dynamic</div>
<div>
routing can be used to propagate information about remote networks.</div>
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<div>
Lecture No. 40</div>
<div>
IP ROUTING (Part-2)</div>
<div>
ROUTING IN THE GLOBAL INTERNET</div>
<div>
As the route information protocol allows one router to exchange routing</div>
<div>
information with another, however this scheme cannot scale to the entire Internet</div>
<div>
because, if all routers attempted to exchange information, the resulting traffic would</div>
<div>
overwhelm the backbone networks. To solve the problem the routers and networks in the</div>
<div>
Internet are divided into groups. All routers within a group exchange routing information.</div>
<div>
Then at least one router in the group summarizes information before sending it to other</div>
<div>
groups.</div>
<div>
AUTONOMOUS SYSTEM CONCEPT:</div>
<div>
An autonomous system can be thought of as a set of networks and routers under one</div>
<div>
administrative authority. The term is flexible. It can be or correspond to an entire</div>
<div>
intuition or a single corporation. It is needed because no routing protocol can scale to</div>
<div>
entire Internet. Each Autonomous System chooses a routing protocol to exchange routing</div>
<div>
information which is summarized before being passed to another group.</div>
<div>
CLASSIFICATION OF INTERNET ROUTING PROTOCOLS:</div>
<div>
There are two broad classes of Internet Routing Protocol:</div>
<div>
INTERIOR GATEWAY PROTOCOLS (IGPs):</div>
<div>
It is used among routers within autonomous system. The destinations lie within IGP.</div>
<div>
EXTERIOR GATEWAY PROTOCOLS (EGPs):</div>
<div>
It is used among autonomous systems. The destinations lie throughout Internet</div>
<div>
ILLUSTRATION OF IGP/EGP USE:</div>
<div>
The following figure illustrates the IGP/EGP use.</div>
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<div>
An Internet routing architecture is shown. Each autonomous system used to</div>
<div>
communicate among autonomous systems chooses an IGP to use</div>
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<div>
Lecture No. 41</div>
<div>
IP ROUTING (Part-3)</div>
<div>
ROUTES AND DATA TRAFFIC:</div>
<div>
Each ISP is an autonomous system that uses an Exterior Gateway Protocol to</div>
<div>
advertise its customer’s networks to other ISPs. After an ISP advertises destination D,</div>
<div>
datagram destined for D can begin to arrive.</div>
<div>
The flow of routers and data is illustrated with ISPs. After a router in ISP advertises</div>
<div>
routes to customers, data can arrive for these customers.</div>
<div>
INTERNET ROUTING PROTOCOLS:</div>
<div>
Following are the Internet Routing Protocols.</div>
<div>
"Border Gateway Protocol (BGP)</div>
<div>
"Routing Information Protocol (RIP)</div>
<div>
"Open Shortest Path First Protocol (OSPF)</div>
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<div>
BORDER GATEWAY PROTOCOL:</div>
<div>
It is most popular Exterior Gateway Protocol in Internet. It has following</div>
<div>
characteristics:</div>
<div>
"It provides routing among autonomous systems (EGP).</div>
<div>
"It provides policies to control routes advertised.</div>
<div>
"It uses reliable transport (TCP).</div>
<div>
"It gives path of autonomous systems for each destination.</div>
<div>
"Currently the EGP is of choice in the Internet.</div>
<div>
"The current version is four (BGP-4).</div>
<div>
"It provides facilities for Transit Routing.</div>
<div>
ROUTING INFORMATION PROTOCOL (RIP):</div>
<div>
It has the following characteristics:</div>
<div>
"It is used for routing within an autonomous system (IGP).</div>
<div>
"Hop Count Metric: RIP measures distance in network hops, where each network</div>
<div>
between the source and destination counts as a single hop.</div>
<div>
"It uses UDP for all message transmissions.</div>
<div>
"RIP is used over LAN. Version 1 of RIP uses hardware broadcast and version 2 allows</div>
<div>
delivery via multicast.</div>
<div>
"It can be used to advertise default route propagation. An organization can use RIP to</div>
<div>
install a default route in each router.</div>
<div>
"It uses distance vector algorithm.</div>
<div>
"RIP allows hosts to listen passively and update its routing table</div>
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<div>
Lecture No. 42</div>
<div>
IP ROUTING (Part-4)</div>
<div>
ILLUSTRATION OF RIP PACKET FORMAT:</div>
<div>
The format of a RIP version 2 update messages is shown in the figure below. The</div>
<div>
message contains a list of destinations and a distance to each. RIP measures distance in</div>
<div>
hops.</div>
<div>
THE OPEN SHORTEST PATH FIRST PROTOCOL (OSPF):</div>
<div>
As the internet grew in size, so did organizations. In particular, large ISPs</div>
<div>
appeared. To satisfy demand for a routing protocol that can scale to large organizations,</div>
<div>
the IETF devised an IGP known as the Open Shortest Path First Protocol (OSPF).</div>
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<div>
THE CHARACTERISTICS OF OSPF:</div>
<div>
OSPF has following characteristics:</div>
<div>
"ROUTING WITHIN AN AUTONOMOUS SYSTEM:</div>
<div>
OSPF has designed as an Interior Gateway Protocol used to pass routing</div>
<div>
information among routers within an autonomous system.</div>
<div>
"FULL CIDR AND SUBNET SUPPORT:</div>
<div>
OSPF includes a 32-bit address mask with each address, which allows the address</div>
<div>
to be classful, classless, or subnetted.</div>
<div>
"AUTHENTICATED MESSAGE EXCHANGE:</div>
<div>
A pair of routers using OSPF can authenticate each message to ensure that</div>
<div>
messages are only accepted from a trusted source.</div>
<div>
"IMPORTED ROUTES:</div>
<div>
OSPF allows a router to introduce routes learned from another means (e.g., from</div>
<div>
BGP).</div>
<div>
"LINK-STATE ALGORITHM:</div>
<div>
OSPF uses link-state routing.</div>
<div>
"SUPPORT FOR MULTI-ACCESS NETWORKS:</div>
<div>
Traditional link state routing is inefficient across a multi-access network, such as</div>
<div>
an Ethernet, because all routers attached to the network broadcast link status. OSPF</div>
<div>
optimizes by designing a single router to broadcast on the network.</div>
<div>
OSPF GRAPH:</div>
<div>
Networks and Routers can be illustrated using OSPF graph. Routers correspond to</div>
<div>
nodes in OSPF graph. Networks correspond to edges. The adjacent pair of routers</div>
<div>
periodically test connectivity and broadcast link-status information to area. Each router</div>
<div>
uses link-status messages to compute shortest paths. An internet consisting of seven</div>
<div>
networks interconnected by routers is shown in the figure below. A corresponding OSPF</div>
<div>
graph is also shown in figure b. In the simplest case; each router corresponds to a node in</div>
<div>
the graph.</div>
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<div>
OSPF AREAS:</div>
<div>
OSPF allows subdivision of Autonomous System into areas. The link-status information</div>
<div>
is propagated within an area. The routes are summarized before being propagated to</div>
<div>
another area. It reduces overhead (less broadcast traffic). Because it allows a manager to</div>
<div>
partition the routers and networks in an autonomous system into multiple areas, OSPF</div>
<div>
can scale to handle a larger number of routers than other IGPs.</div>
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<div>
Lecture No. 43</div>
<div>
IP ROUTING (Part-5)</div>
<div>
INTERNET MULTICAST ROUTING:</div>
<div>
Internet multicast routing is difficult because internet multicast allows arbitrary</div>
<div>
computer to join multicast group at any time. It allows arbitrary member to leave</div>
<div>
multicast group at any time. It also allows arbitrary computer to send message to a group</div>
<div>
(even if not a member).</div>
<div>
IP MULTICAST SEMANTICS:</div>
<div>
IP multicast group is anonymous in two ways:</div>
<div>
1. Neither a sender nor a receiver knows the identity or the number of group</div>
<div>
members.</div>
<div>
2. Routers and hosts do not know which applications will send a datagram to a</div>
<div>
group.</div>
<div>
IGMP:</div>
<div>
A standard protocol exists that allows a host to inform a nearby router whenever</div>
<div>
the host needs to join or leave a particular multicast group known as Internet Group</div>
<div>
Multicast Protocol (IGMP). The computer uses IGMP to inform the local router about the</div>
<div>
last application when it leaves.</div>
<div>
FORWARDING AND DISCOVERY TECHNIQUES:</div>
<div>
Routers not hosts have responsibility for the propagation of multicast routing</div>
<div>
information. The size and topology of groups may vary e.g. Teleconferencing often</div>
<div>
creates small groups and on the other side web casting can create a large group.</div>
<div>
APPROACHES FOR DATAGRAM FORWARDING:</div>
<div>
In practice multicast protocols have followed three different approaches for datagram</div>
<div>
forwarding:</div>
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<div>
FLOOD-AND-PRUNE:</div>
<div>
Flood-and-prune is ideal in a situation where the group is small and all members</div>
<div>
are attached to contiguous Local Area Networks. To avoid routing loops, flood-and-prune</div>
<div>
protocols use a technique known as Reverse Path Broadcasting (RPB) that breaks cycles.</div>
<div>
CONFIGURATION-AND-TUNNELING:</div>
<div>
Configuration-and-tunneling is ideal in a situation where the group is</div>
<div>
geographically dispersed (i-e., has a few members at each site, with sites separated by</div>
<div>
long distances). When a multicast datagram arrives, the routers at a site transmit the</div>
<div>
datagram on all directly attached LANs via hardware multicast. The router then consults</div>
<div>
its configuration table to determine which other sites should receive a copy. The router</div>
<div>
uses IP-in-IP tunneling to transfer a copy of the multicast datagram to other sites.</div>
<div>
CORE-BASED DISCOVERY:</div>
<div>
To provide smooth growth, some multicast routing protocols designate a core</div>
<div>
unicast address for each multicast group. Whenever a router R1 needs to reach a group,</div>
<div>
R1 sends a datagram to the groups core address. As the datagram travels through the</div>
<div>
Internet, each router examines the contents. When the datagram reaches a router R2 that</div>
<div>
participates in the group, R2 removes and processes the message. If the message contains</div>
<div>
a multicast datagram switch a destination address equal to the group_s address, R2</div>
<div>
forwards the datagram to members of the group. If the message contains a request to join</div>
<div>
the group, R2 adds the information to its routes, and then uses IP-in-IP to forward a copy</div>
<div>
of each multicast datagram to R1. Thus the set of routers participating in a multicast</div>
<div>
group grows from the core outward. In graph theoretic terms, the set forms a tree.</div>
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Lecture No. 44</div>
<div>
IP ROUTING (Part-6)</div>
<div>
MULTICAST PROTOCOLS:</div>
<div>
Several multicast protocols exist. Some of the proposed protocols are:</div>
<div>
DISTANCE VECTOR MULTICAST ROUTING PROTOCOL</div>
<div>
(DVMRP):</div>
<div>
This protocol is used by the Unix program mrouted and the Internet Multicast</div>
<div>
backBONE (MBONE). DVMRP performs local multicast and uses IP-in-IP encapsulation</div>
<div>
to send multicast datagrams from one site on the Internet to another.</div>
<div>
CORE BASED TREES (CBT):</div>
<div>
A multicast routing scheme in which the protocol software builds a delivery tree</div>
<div>
from a central point. When a user joins a group, routers send a message toward the</div>
<div>
central point (i.e., the core) to search for the nearest participating router.</div>
<div>
PROTOCOL INDEPENDENT MULTICAST_ SPARSE MODE</div>
<div>
(PIM-SM):</div>
<div>
This is a protocol that uses the same approach as CBT to form a multicast routing</div>
<div>
tree. The designers chose the term protocol independent to emphasize that although</div>
<div>
unicast datagrams are used to contact remote destinations when establishing multicast</div>
<div>
forwarding. PIM-SM does not depend on any particular unicast routing protocol.</div>
<div>
PROTOCOL INDEPENDENT MULTICAST _ DENSE MODE</div>
<div>
(PIM-DM):</div>
<div>
A protocol designed for use within an organization. Routers that use PIM-DM</div>
<div>
broadcast (i.e. flood) multicast packets to all locations within the organization. Each</div>
<div>
router that has no member of a particular group sends back a message to prune the</div>
<div>
multicast routing tree ((i.e., a request to stop the flow of packets). The scheme works well</div>
<div>
for short-lived multicast sessions (e.g., a few minutes) because it does not require setup</div>
<div>
before transmission begins.</div>
<div>
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<div>
MULTICAST EXTENSIONS TO THE OPEN SHORTEST PATH</div>
<div>
FIRST PROTOCOL (MOSPF):</div>
<div>
A protocol designed for use within an organization. MOSPF builds on OSPF and</div>
<div>
reuses many of the same basic concepts and facilities.</div>
<div>
None of the above mentioned protocols is best in all circumstances.</div>
<div>
CLIENT-SERVER INTERACTION:</div>
<div>
Although an internet system provides basic communication service, the protocol</div>
<div>
software cannot initiate contact with, or accept contact from, a remote computer. Instead</div>
<div>
two application programs must participate in any communication i.e. one application</div>
<div>
initiates communication and the other accepts it.</div>
<div>
HOW TWO APPLICATION PROGRAMS MAKE CONTACT?</div>
<div>
The two application programs make contact in the following way:</div>
<div>
One application actively begins execution first and another application waits</div>
<div>
passively at prearranged location. This process is called client-server interaction.</div>
<div>
CLIENT-SERVER PARADIGM:</div>
<div>
It is used by all network applications. The passive program is called a server and</div>
<div>
the active program is called a client.</div>
<div>
CHARACTERISTICS OF A CLIENT:</div>
<div>
The characteristics of a client are explained below:</div>
<div>
"Client is an arbitrary application program.</div>
<div>
"It becomes client temporarily.</div>
<div>
"It can also perform other computations.</div>
<div>
"It is invoked directly by the user.</div>
<div>
"It runs locally on the user’s computer.</div>
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<div>
"It actively initiates contact with a server.</div>
<div>
"It contacts one server at a time.</div>
<div>
CHARACTERISTICS OF A SERVER:</div>
<div>
The characteristics of a server are explained below:</div>
<div>
"It is a special-purpose, privileged program.</div>
<div>
"It is dedicated to provide one service.</div>
<div>
"It can handle multiple remote clients simultaneously.</div>
<div>
"It invoked automatically when system boots.</div>
<div>
"It executes forever.</div>
<div>
"It needs powerful computer and operating system.</div>
<div>
"It waits for client contact.</div>
<div>
"It accepts requests from arbitrary clients.</div>
<div>
TRANSPORT PROTOCOLS AND CLIENT-SERVER</div>
<div>
NTERACTION</div>
<div>
Like most application programs, a client and server use a transport protocol to</div>
<div>
communicate. For example, the figure below illustrates a client and server using the</div>
<div>
TCP/IP stack.</div>
<div>
In the figure, a client and server using TCP/IP protocols to communicate across an</div>
<div>
Internet are shown. The client and server each interact with a protocol in the transport</div>
<div>
layer.</div>
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<div>
Lecture No. 45</div>
<div>
COURSE REVISION</div>
<div>
COURSE SUMMARY</div>
<div>
(This lecture contains the summary of the topics that were covered during the course.)</div>
<div>
SYLLABUS FOR FINALS:</div>
<div>
The syllabus of the course is given as follows:</div>
<div>
PACKET TRANSMISSION:</div>
<div>
• Packets, Frames and Error Detection</div>
<div>
• LAN Technologies and Network Topologies</div>
<div>
• Hardware Addressing and Frame Type Identification</div>
<div>
• LAN Wiring, Physical Topology, And Interface Hardware</div>
<div>
• Extending LANs</div>
<div>
• WAN Technologies and Routing</div>
<div>
• Connection-Oriented Networking and ATM</div>
<div>
• Network Characteristics</div>
<div>
INTERNETWORKING:</div>
<div>
• Internetworking Concepts, Architecture and Protocols</div>
<div>
• IP Addressing</div>
<div>
• Binding Protocol Addresses (ARP)</div>
<div>
• IP Datagrams and Datagram Forwarding</div>
<div>
• IP Encapsulation, Fragmentation and Reassembly</div>
<div>
• UDP: Datagram Transport Service</div>
<div>
• TCP: Reliable Transport Service</div>
<div>
• Internet Routing</div>
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<div>
PACKET TRANSMISSION</div>
<div>
In this portion, following chapters were covered. The topics are also given below:</div>
<div>
PACKETS, FRAMES AND ERROR DETECTION</div>
<div>
• The Concepts of Packets</div>
<div>
• Packets and Time-Division Multiplexing</div>
<div>
• Packets and Hardware Frames</div>
<div>
• Byte Stuffing</div>
<div>
• Transmission Errors</div>
<div>
• Parity Bits and Parity Checking</div>
<div>
• Probability, Mathematics, and Error Detection</div>
<div>
• Detecting Errors with Checksums</div>
<div>
• Detecting Errors with Cyclic Redundancy Checks</div>
<div>
• Combining Building Blocks</div>
<div>
• Burst Errors</div>
<div>
• Frame Format and Error Detection Mechanisms</div>
<div>
LAN TECHNOLOGY AND NETWORK TOPOLOGY</div>
<div>
• Direct Point-to-Point Communication</div>
<div>
• Shared Communication Channels</div>
<div>
• Significance of LANs and Locality of Reference</div>
<div>
• LAN Topologies</div>
<div>
o Star Topology</div>
<div>
o Ring Topology</div>
<div>
o Bus Topology</div>
<div>
• Example Bus Network: Ethernet</div>
<div>
• Carrier Sense on Multi-Access Networks (CSMA)</div>
<div>
• Collision Detection and Backoff with CSMA/CD</div>
<div>
• 802.11 Wireless LANs and CSMA/CA</div>
<div>
• Local Talk</div>
<div>
• IBM Token Ring</div>
<div>
• FDDI</div>
<div>
• ATM</div>
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<div>
HARDWARE ADDRESSING AND FRAME TYPE</div>
<div>
DENTIFICATION</div>
<div>
• How LAN Hardware uses Addresses to Filter Packets</div>
<div>
• Format of a Physical Address</div>
<div>
• Broadcasting</div>
<div>
• Multicasting</div>
<div>
• Multicast Addressing</div>
<div>
• Identifying Packet Contents</div>
<div>
• Frame Headers and Frame Format</div>
<div>
• Network Analyzers, Physical Addresses, Frame Types</div>
<div>
LAN WIRING, PHYSICAL TOPOLOGY, AND INTERFACE</div>
<div>
HARDWARE</div>
<div>
• Speeds of LANs and Computers</div>
<div>
• Network Interface Hardware</div>
<div>
• Original Thick Ethernet Wiring</div>
<div>
• Connection Multiplexing</div>
<div>
• Thin Ethernet Wiring</div>
<div>
• Twisted Pair Ethernet</div>
<div>
• Advantages and Disadvantages of Wiring Schemes</div>
<div>
• The Topology Paradox</div>
<div>
• Network Interface Cards and Wiring Schemes</div>
<div>
• 10/100 Network Interfaces</div>
<div>
• Categories of Wires</div>
<div>
• Wiring Schemes and Other Network Technologies</div>
<div>
EXTENDING LANs: FIBER MODEMS, REPEATERS,</div>
<div>
BRIDGES, AND SWITCHES</div>
<div>
• Distance Limitation and LAN Design</div>
<div>
• Fiber Optic Extensions</div>
<div>
• Repeaters</div>
<div>
• Bridges</div>
<div>
• Frame Filtering</div>
<div>
• Planning a Bridged Network</div>
<div>
• Bridging Between Buildings</div>
<div>
• Bridging across Longer Distances</div>
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<div>
• A Cycle of Bridges</div>
<div>
• Distributed Spanning Tree</div>
<div>
• Switching</div>
<div>
• Combining Switches and Hubs</div>
<div>
• Bridging and Switching with Other Technologies</div>
<div>
WAN TECHNOLOGIES AND ROUTING</div>
<div>
• Large Networks and Wide Areas</div>
<div>
• Packet Switches</div>
<div>
• Forming A WAN</div>
<div>
• Store and Forward</div>
<div>
• Physical Addressing in a WAN</div>
<div>
• Next-Hop Forwarding</div>
<div>
• Source Independence</div>
<div>
• Relationship of Hierarchical Addresses to Routing</div>
<div>
• Routing in a WAN</div>
<div>
• Use of Default Routes</div>
<div>
• Routing Table Computation</div>
<div>
• Shortest Path Computation in a Graph</div>
<div>
• Distributed Route Computation</div>
<div>
• Distance Vector Routing</div>
<div>
• Link-State Routing (SPF)</div>
<div>
• Example WAN Technologies</div>
<div>
o ARPANET</div>
<div>
o FRAME RELAY</div>
<div>
o SMDS</div>
<div>
o ATM</div>
<div>
CONNECTION-ORIENTED NETWORKING AND ATM</div>
<div>
• A Single Global Network</div>
<div>
• ISDN and ATM</div>
<div>
• ATM Design and Cells</div>
<div>
• Connection-Oriented Service</div>
<div>
• VPI/VCI</div>
<div>
• Labels and Label Switching</div>
<div>
• Permanent Virtual Circuits</div>
<div>
• Switched Virtual Circuits</div>
<div>
• Quality of Service</div>
<div>
• The Motivation for Cells and Label Switching</div>
<div>
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<div>
• ATM Data Transmission and AAL5</div>
<div>
• Critique of ATM</div>
<div>
NETWORK CHARACTERISTICS: OWNERSHIP, SERVICE</div>
<div>
PARADIGM AND PERFORMANCE</div>
<div>
• Network Ownership</div>
<div>
• Privacy and Public Networks</div>
<div>
• Advantages and Disadvantages</div>
<div>
• Virtual Private Networks</div>
<div>
• Guaranteeing Absolute Privacy</div>
<div>
• Service Paradigm</div>
<div>
• Connection-Oriented Service Paradigm</div>
<div>
• Connectionless Service Paradigm</div>
<div>
• Interior and Exterior Service Paradigm</div>
<div>
• Comparison of Service Paradigm</div>
<div>
• Addresses of Connection Identifiers</div>
<div>
• Network Performance Characteristics</div>
<div>
o Delay</div>
<div>
o Throughput</div>
<div>
• Jitter</div>
<div>
INTERNETWORKING</div>
<div>
In this portion the following chapters were covered. The topics are also given below:</div>
<div>
INTERNETWORKING: CONCEPTS, ARCHITECTURE, AND</div>
<div>
PROTOCOLS</div>
<div>
• The Motivation for Internetworking</div>
<div>
• The Concept of Universal Service</div>
<div>
• Universal Service in a Heterogeneous World</div>
<div>
• Internetworking</div>
<div>
• Physical Network Connection with Routers</div>
<div>
• Internet Architecture</div>
<div>
• Achieving Universal Service</div>
<div>
• A Virtual Network</div>
<div>
• Protocols for Internetworking</div>
<div>
• Layering and TCP/IP Protocols</div>
<div>
• Host Computers, Routers and Protocol Layers</div>
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<div>
IP: INTERNET PROTOCOL ADDRESSES</div>
<div>
• Addresses for the Virtual Internet</div>
<div>
• The IP Addressing Scheme</div>
<div>
• The IP Address Hierarchy</div>
<div>
• Original Classes of IP Addresses</div>
<div>
• Computing the Class of an Address</div>
<div>
• Dotted Decimal Notation</div>
<div>
• Classes and Dotted Decimal Notation</div>
<div>
• Division of the Address Space</div>
<div>
• Authority for Addresses</div>
<div>
• A Classful Addressing Example</div>
<div>
• Subnet and Classless Addressing</div>
<div>
• Address Masks</div>
<div>
• CIDR Notation</div>
<div>
• A CIDR Address Block Example</div>
<div>
• CIDR Host Addresses</div>
<div>
• Special IP Addresses</div>
<div>
• The Berkeley Broadcast Address Form</div>
<div>
• Routers and the IP Addressing Principle</div>
<div>
• Multi-Homed Hosts</div>
<div>
BINDING PROTOCOL ADDRESSES (ARP)</div>
<div>
• Protocol Addresses and Packet Delivery</div>
<div>
• Address Resolution</div>
<div>
• Address Resolution Techniques</div>
<div>
• Address Resolution with Table Lookup</div>
<div>
• Address Resolution with Closed-Form Computation</div>
<div>
• Address Resolution with Message Exchange</div>
<div>
• Address Resolution Protocol</div>
<div>
• ARP Message Delivery</div>
<div>
• ARP Message Format</div>
<div>
• Sending an ARP Message</div>
<div>
• Identifying ARP Frames</div>
<div>
• Caching ARP Responses</div>
<div>
• Processing an Incoming ARP Message</div>
<div>
• Layering, Address Resolution, Protocol Addresses</div>
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<div>
IP DATAGRAMS AND DATAGRAM FORWARDING</div>
<div>
• Connectionless Service</div>
<div>
• Virtual Packets</div>
<div>
• The IP Datagram</div>
<div>
• Forwarding an IP Datagram</div>
<div>
• IP Addresses and Routing Table Entries</div>
<div>
• The Mask Field and Datagram Forwarding</div>
<div>
• Destination and Next-Hop Addresses</div>
<div>
• Best-Effort Delivery</div>
<div>
• The IP Datagram Header Format</div>
<div>
IP ENCAPSULATION, FRAGMENTATION, AND</div>
<div>
REASSEMBLY</div>
<div>
• Datagram Transmission and Frames</div>
<div>
• Encapsulation</div>
<div>
• Transmission across an Internet</div>
<div>
• MTU, Datagram Size, and Encapsulation</div>
<div>
• Reassembly</div>
<div>
• Identifying a Datagram</div>
<div>
• Fragment Loss</div>
<div>
• Fragmenting a Fragment</div>
<div>
THE FUTURE IP (IPv6)</div>
<div>
• The Success of IP</div>
<div>
• The Motivation for change</div>
<div>
• A Name and a Version Number</div>
<div>
• IPv6 Datagram Format</div>
<div>
• IPv6 Base Header Format</div>
<div>
• How IP v6 handles Multiple Headers</div>
<div>
• Fragmentation, Reassembly, and Path MTU</div>
<div>
• The Purpose of Multiple Headers</div>
<div>
• IPv6 Addressing</div>
<div>
• IPv6 Colon Hexadecimal Notation</div>
<div>
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<div>
UDP: DATAGRAM TRANSPORT SERVICE</div>
<div>
• Need for End-to-End Transport Protocols</div>
<div>
• The User Datagram Protocol</div>
<div>
• Connection-less Paradigm</div>
<div>
• Message Oriented Interface</div>
<div>
• UDP Communication Semantics</div>
<div>
• Arbitrary Interaction</div>
<div>
• End Point Identification with Protocol Port Numbers</div>
<div>
• UDP Datagram Format</div>
<div>
TCP: RELIABLE TRANSPORT SERVICE</div>
<div>
• The Need for Reliable Transport</div>
<div>
• The Transmission Control Protocol</div>
<div>
• The Service TCP Provides to Applications</div>
<div>
• End-To-End Service and Datagrams</div>
<div>
• Achieving Reliability</div>
<div>
• Packet Loss and Retransmission Times</div>
<div>
• Adaptive Retransmission</div>
<div>
• Buffers, Flow Control, and Windows</div>
<div>
• Three-Way Handshake</div>
<div>
• Congestion Control</div>
<div>
• TCP Segment Format</div>
<div>
INTERNET ROUTING</div>
<div>
• Static Vs Dynamic Routing</div>
<div>
• Static Routing In Hosts and a Default Route</div>
<div>
• Dynamic Routing and Routers</div>
<div>
• Routing in the Global Internet</div>
<div>
• Autonomous System Concept</div>
<div>
• The Two Types of Internet Routing Protocols (IGP & EGP)</div>
<div>
• Routes and Data Traffic</div>
<div>
• Border Gateway Protocol (BGP)</div>
<div>
• The Routing Information Protocol (RIP)</div>
<div>
• RIP Packet Format</div>
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<div>
• The Open Shortest Path First Protocol (OSPF)</div>
<div>
• An Example OSPF Graph</div>
<div>
• OSPF Areas</div>
<div>
• Multicast Routing</div>
</div>
<div>
<b><span style="font-size: large;"><a href="http://www.genrica.com/vustuff/BIT710/BIT710_handouts_1_45.pdf" target="_blank"><br /></a></span></b></div>
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<b><span style="font-size: large;"><a href="http://www.genrica.com/vustuff/BIT710/BIT710_handouts_1_45.pdf" target="_blank">Computer Network BIT710/COMPUTER NETWORKS CS610 book HANDOUTS in pdf</a></span></b></div>
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Computer Network BIT710/COMPUTER NETWORKS CS610 book HANDOUTS in pdf

Computer Network BIT710/COMPUTER NETWORKS CS610 book HANDOUTS in pdf Handouts | Lectures | Contents | Books COMPUTER NETWORKS (CS610...