1、Jing Xu (徐晶)Dept. of Electronics and Information Eng.Huazhong University of Science and TechnologyMay. 2012Lecture 1lIntroduction of the courselWhat & WhylGoalslTextbooklEvaluationlBackground lChapter 1. Foundation-2-What is this Course All AboutlFundamental principles of Computer NetworkslFirst cou

2、rse Broad coverage of topics (important topics in depth)lTopics categorized to:lnetwork architectures - technologieslprotocolslapplicationslWe will not discuss specific implementations: le.g., how to configure the latest cisco routers-3-Why Learn about Networking?lIndispensable part of modern societ

3、ylCommercial e-commerce, banking, inventorying, telecommunications, archiving, healthlSocial critical infrastructure, homeland security, policinglHuman interaction/communication email, chat, videoconferencing, social networking, entertainmentlAppears in every facet of engineeringlModern trend Networ

4、k every (electronic) device (computers, phones, sensors, planes, cars, TVs, appliances, heart monitors, )lProlific field to pursue graduate studieslMany problems remain unsolvedlResearch funding is still strong-4-GoalslDevelop a fundamental understanding of the network design principles and performa

5、nce metricslBecome familiar with the mechanisms and protocols for reliable data communication via a computer networklBe able to evaluate the performance of various network technologies and protocolslThink as an engineer: What technologies should be employed to build a network with particular specifi

6、cations?lDevelop interest in performing research in the area of Computer Networks-5-Textbook lRequired Textbookl1 L. L. Peterson & B. S. Davie, Computer Networks: A Systems Approach, 3rd or 4th Edition, Morgan KaufmannlProblem driven: scenario and challenges lRequirements General solutions Real prot

7、ocolslHelpful to grasp the principles of network-6-Textbook lAlternative/additional textbooks: l2 James F. Kurose and Keith W. Ross, Computer Networking, A Top-Down Approach Featuring the Internet, 3rd Edition or 4th Edition, lApplication driven: functions and performancelHelpful to develop new serv

8、ice/application cross layers-7-Textbook lAdditional textbooks: l3 Andrew Tanenbaum, Computer Networks, 3rd or 4th Edition, lTraditional and classical layering view on networkslFrom different physical elements to various applicationsl4 謝希仁，計算機網(wǎng)絡，第4版 或 第5版，電子工業(yè)出版社lWidely used in China, take much refer

9、ence from 334-8-Evaluation lEvaluation CriterionlElementslLecture & Experiments Attendee (20%)lHomework assignments (20%)lFinal Examination (60%)lOptional credits (up to 15%)lSome advanced topics will be given in the homeworklAdditional credits will be awarded to the best solutions-9-Lecture 1lIntro

10、duction of the courselBackground lChapter 1. Foundation-10-NetworklA system that carries a commodity between 2 or more entitieslExamples: Transportation network, electric grid, postal, water, telephoneComputer network: A system that carries information between 2 or more entities, in the form of elec

11、tric signals -11-Network ElementslNodes: Special purpose deviceslLinks: Connections between nodesPCserverswitchbridgerouterOptical fiberCoaxial cablewireless-12-Network DesignlThe task of connecting nodes via links, so that nodes can exchange information, reliably, timely, efficiently, safely, priva

12、tely, “greenly”, and with low cost.lNeed to define the network architecture, protocols, applications, interfaces, policies, usages. lWe follow the system approach to investigate such a topic-13-What is system approach?1.Identify the target system2.General computer network3.Requirement analysis4.Back

13、ground of existed technologies5.Expectations: characteristics, functions, performances6.Design7.Architecture design: building blocks, modules, interfaces8.Module design: protocols, hardware, software9.Implementation10.System development, software coding, .11.Test 12.Performance metrics-14-Problem in

14、 Chapter1 :Building a Network-15-Lecture 1lIntroduction of the courselBackgroundlChapter 1. FoundationlProblem: building a networkl1.1 Applicationsl1.2 Requirementsl1.3 Network Architecturel1.4 Implementing Network Softwarel1.5 Performancel1.6 History story l1.7 Summary-16-What Drives Network Design

15、?lApplicationslWWW, email, chat, videoconferencing, e-commerce, audio/video streaming, VOIP, file sharinglWho deploys the networklEnterprise, government, end-userlWhere is the network deployed lHome, building, campus, state, country, continent, globe -17-1.2 Requirementsl1.2.1 ConnectivitylProvide c

16、onnectivity among a set of computersl1.2.2 Cost-effective resource sharinglProvide efficiency under resource constraintl1.2.3 Support for common serviceslProvide general communication pattern for diverse applicationslProvide reliability under partial failure -18-1.2.1 ConnectivitylNodes (wide-sense)

17、lhost: connected computerslnode (narrow-sense): intermediate nodeslLinkslpoint-to-point linklmultiple-access linkl(shared media link)The simplest case: directly connection (one link)linklinkhosthost-19-1.2.1 ConnectivitylSwitched networks lA kind of element networkslTwo types of switched network (no

18、t only computer network): circuit-switched, packet-switchedMore complex case: Indirect connection (more links)a cloud is used to denote any type of network, whether it is a single point-to-point link, a multiple-access link, or a switched network. switchhost-20-1.2.1 ConnectivitylInternetwork lA set

19、 of independent networks (clouds) are interconnected to form an internetworkMost complex case: Internetwork (more networks)Router/gateway: A node specialized to connect two or more networksnetworkhostrouter-21-1.2.1 ConnectivitylHost-to-host connectivityl(1) setup direct or indirect connection among

20、 a set of computersl(2) identify a node in a network AddressinglAddresslA byte string that identifies a host or nodelRoutelWhere to forward messages toward the destination node lForwarding based on destination addresslUnicast: one-to-onelMulticast: one-to-manylBroadcast: one-to-all-22-1.2.1 Connecti

21、vitylSummarylA network can be defined recursively as consisting of ltwo or more nodes connected by a physical link lor as two or more networks connected by a nodelChallengeslHow to define an address for each node? lHow to use this address to route messages toward the appropriate destination node(s)

22、?-23-1.2 Requirementsl1.2.1 ConnectivitylProvide connectivity among a set of computerslRequired: naming and routing l1.2.2 Cost-effective resource sharinglProvide efficiency under resource constraintl1.2.3 Support for common serviceslProvide general communication pattern for diverse applicationslPro

23、vide reliability under partial failure -24-1.2.2 Cost-effective resource sharinglRequirement beyond Connectivity lAll pairs of hosts are able to exchange messages at the same timelTo be fit for the burst of computer communicationlEfficiently and fairly share the limited network resourcelConsidering

24、the switched network in details, and investigate its resource sharing strategy lSwitched networklMultiplexing-25-Taxonomy of Communication NetworkslCommunication networks can be classified based on the way in which the nodes exchange information:Communication NetworkSwitched NetworkBroadcast Network

25、Packet-Switched NetworkVirtual Circuit NetworkTwo kind of switched networks discussed in following. .-26-Switched NetworkslCircuit-Switched lA dedicated circuit is established across a set of linkslExample: Telephone networklPacket-SwitchedlData is split into blocks called packets or messages. lStor

26、e-and-forward strategylSwitches: Store and forward packetsterminal/ hostswitch-27-Circuit-Switched NetworkslEnd-to-end permanent connectionlDedicated path for communicationlNo need for a destination address since a path is already establishedlOnce communication is complete, connection is ended and l

27、inks are released. -28-Circuit Switching: Intermediate Nodeincoming linksoutgoing linksIntermediate Node(Switch)-29-Circuit Switching: TimingDATAHost 1Host 2Node 1Node 2propagation delay between Host 1 and Node 1propagation delay between Host 2 and Node 1processing delay at Node 1Circuit Establishme

28、nt Data Transmission Circuit Termination -30-Advantages of Circuit SwitchinglGuaranteed bandwidth (Quality of Service)lPredictable bitrate and delaylGood for delay-sensitive applicationslReliable communicationlRare packet losslPackets are delivered in orderlSimple data routinglForwarding based on ti

29、me slot or frequency (multiplexing)lNo need to inspect a packet header for addresslLow per-packet overheadlForwarding based on time slot or frequencylNo IP (and TCP/UDP) header on each packet-31-Disadvantages of Circuit SwitchinglWasted bandwidthlBursty traffic leads to idle connection during silent

30、 periodlBlocked connectionslConnection refused when resources are not sufficientlUnable to offer “okay” service to everybodylConnection set-up delay lNo communication until the connection is set uplUnable to avoid extra latency for small data transferslNetwork statelNetwork nodes must store per-conn

31、ection informationlUnable to avoid per-connection storage and state-32-Packet Switched NetworkslData is divided into packets (messages)lEach packet contains identification info (source/destination address seq. number, etc)lPackets traverse the network individuallylUse the destination address to forw

32、ard packetsl May use more than one routes, nodes may store packets temporarily-33-Packet Switching: Intermediate Nodeincoming linksoutgoing linksIntermediate Node(Switch)MemoryCongested: If a switch receive packets faster than it can send them for an period of time, then the switch will run out of b

33、uffer space, and some packets will have to be dropped. Stored-and-forward-34-Packet Switching: TimingPacket 1Packet 2Packet 3Packet 1Packet 2Packet 3Packet 1Packet 2Packet 3processing delay of Packet 1 at Node 2Host 1Host 2Node 1Node 2propagationdelay betweenHost 1 and Node 2 transmission time of Pa

34、cket 1at Host 1Store-and-forward strategy is more efficient-35-Advantages of Packet SwitchinglNo wasted bandwidth (not entirely true)lLinks are not reserved during idle periodlMultiplexing (see next slides)lFrequency, time, statistical multiplexinglServicelMore connections of lesser qualitylNo block

35、ing of userslAdaptationlCan adapt to network congestion and failures-36-Multiplexing MethodslTime Division MultiplexinglFrequency Division MultiplexingS1S2S3S1S2S3S1S2S3S1S2S3timetimefrequencyS3S1S2f1f2f3-37-Multiplexing MethodslStatistical multiplexinglDivision of the communication medium into a nu

36、mber of channels of variable bandwidth-38-Deterministic vs. Statistical MultiplexingDeterministic Multiplexing Statistical Multiplexing-39-Disadvantages of Packet SwitchinglNo guaranteed bandwidthlHarder to build applications requiring QoSlPer packet overheadlNeed a header with source/dest. address,

37、 etc.lComplex end-to-end controllPackets can be lost, corrupted or delivered out-of-orderlDelay and CongestionlNo congestion control, can lead to arbitrary delays and packet drops-40-1.2.2 Cost-effective resource sharinglSummarylStatistical multiplexing defines a cost-effective way for multiple user

38、s to share network resourceslPacket is defined as the granularity with which the links of the network are allocated to different flowslEach switch is able to schedule the use of the physical links it is connected to on a per-packet basis. lChallenges lFairly allocate link capacity to different flows

39、 lDeal with congestion when it occurs-41-1.2 Requirementsl1.2.1 ConnectivitylProvide connectivity among a set of computerslRequired: naming and routing l1.2.2 Cost-effective resource sharinglProvide efficiency under resource constraintlRequired: packet-switched networking, resource allocationl1.2.3

40、Support for common serviceslProvide general communication pattern for diverse applicationslProvide reliability under partial failure -42-1.2.3 Support for common servicesSample 1: Host A send a text file in 1Mb size to Host BSample 2: Host A request streaming video from Host BHostHostHostSample1 App

41、licationHostApplicationHostSample2Host AHost B-43-Common ServiceslCommon serviceslSome building blocks that can be invoked repeatedly by applicationslCommon communication patternslThe characteristics of common serviceslTwo communication patternslRequest/Reply: guarantee that every message sent by on

42、e side is received by the other side, and only one copy of each message is delivered.lMessage stream: support both one-way and two-way traffic and to support different delay properties, ensure that those messages arrive in the same order in which they were sent, support multicast.-44-Common ServicesHostHostHostChannelApplicationHostApplicationHostHost AHost BHostHostHostChannelApplicationHostApplicationHostHost AHost BSimple host, Complex NetworkSample: telephone networkComplex host, Simple NetworkSample: Internet-45-Telephone Network: Dumb Edge, Smart CorelDumb phoneslDial a numberlSpeak and