計(jì)算機(jī)網(wǎng)絡(luò)和協(xié)議分析ppt課件

1、Advanced Computer Networks計(jì)算機(jī)網(wǎng)絡(luò)Weihong Chen Department of Computer ScienceHunan City UniversitySep, 2010ReviewNetwork Hardware The transmission techniques: Broadcasting links, Point-to-point links The types of the networks by scale: LAN,MAN,WANNetwork software Protocol Hierarchies Design Issues for

2、the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to ProtocolsSpring10 CNConnection-Oriented and Connectionless Servicesconnection-orientedconnectionless Connection-oriented service is modeled after the telephone system. Connectionless service

3、 is modeled after the postal system.It just sends the data.Three phases: set up a connection, data transmission, release the connection.Spring10 CNThe Relationship of Services to ProtocolsServices and protocols are distinct concepts.Fig.6 The relationship between a service and a protocolService prov

4、ided by layer kProtocol A service is a set of primitives (operations) that a layer provides to the layer above it. A service relates to an interface between two layers, with the lower layer being the service provider and the upper layer being the service user. A protocol, in contrast, is a set of ru

5、les governing the format and meaning of the packets, or messages that are exchanged by the peer entities within a layer. Entities use protocols to implement their service definitions. BackSpring10 CN第一章第一章 引言引言Chapter 1 IntroductionSpring10 CNWeihong Chen4. Network Software Protocol Hierarchies Desi

6、gn Issues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to ProtocolsSpring10 CNWeihong Chen 協(xié)議層次協(xié)議層次 典型的設(shè)計(jì)問(wèn)題典型的設(shè)計(jì)問(wèn)題 面向連接和無(wú)連接服務(wù)面向連接和無(wú)連接服務(wù) 服務(wù)原語(yǔ)服務(wù)原語(yǔ) 服務(wù)和協(xié)議的關(guān)系服務(wù)和協(xié)議的關(guān)系Spring10 CNWeihong Chen4.1 Protocol Hierarchies To reduce their design co

7、mplexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. The number of layers, the name of each layer, the contents of each layer, and the function of each layer differ from network to network. The purpose of each layer is to offer certain services

8、to the higher layers, shielding those layers from the details of how the offered services are actually implemented. In a sense, each layer is a kind of virtual machine, offering certain services to the layer above it.Spring10 CNWeihong Chen分層的好處分層的好處 各層之間是獨(dú)立的各層之間是獨(dú)立的; 靈活性好靈活性好; 結(jié)構(gòu)上可分割開(kāi)結(jié)構(gòu)上可分割開(kāi); 易于實(shí)現(xiàn)和

9、維護(hù)易于實(shí)現(xiàn)和維護(hù); 能促進(jìn)標(biāo)準(zhǔn)化工作能促進(jìn)標(biāo)準(zhǔn)化工作;Spring10 CNWeihong ChenSpring10 CNFig.9 Protocol Hierarchies A protocol is an agreement between the communicating parties on how communication is to proceed. It contains three elements: syntax, meaning and synchronization.The entities comprising the corresponding layers o

10、n different machines are called peers.Between each pair of adjacent layers is an interface. A set of layers and protocols is called a network architecture. Spring10 CN In reality, no data are directly transferred from layer n on one machine to layer n on another machine. Instead, each layer passes d

11、ata and control information to the layer immediately below it, until the lowest layer is reached. Below layer 1 is the physical medium through which actual communication occurs. In Fig.9, virtual communication is shown by dotted lines and physical communication by solid lines.Spring10 CN101010000111

12、0110100110100101Communication on different machines 5432154321Computer 1AP2AP1Computer 2H5H4H5H4H3H5321H2H4H3H5H5H4H5H4H3H5H2H4H3H5RouterSpring10 CNWeihong ChenFig. 10 Example information flow supporting virtual communication in layer 5Spring10 CNWeihong Chen一些概念一些概念 對(duì)等實(shí)體：在不同的系統(tǒng)中位于同一層次上的實(shí)體。（不對(duì)等實(shí)體：在不

13、同的系統(tǒng)中位于同一層次上的實(shí)體。（不同系統(tǒng)之間的通信實(shí)際上就是各對(duì)等實(shí)體之間的通信。）同系統(tǒng)之間的通信實(shí)際上就是各對(duì)等實(shí)體之間的通信。） 協(xié)議：對(duì)等實(shí)體間通信所需遵循的規(guī)則的總和。協(xié)議：對(duì)等實(shí)體間通信所需遵循的規(guī)則的總和。 接口：定義了上層調(diào)用下層服務(wù)的原語(yǔ)操作。接口：定義了上層調(diào)用下層服務(wù)的原語(yǔ)操作。 網(wǎng)絡(luò)體系結(jié)構(gòu)：層次與協(xié)議的集合。網(wǎng)絡(luò)體系結(jié)構(gòu)：層次與協(xié)議的集合。 協(xié)議棧：將系統(tǒng)使用的協(xié)議按層次順序（每層一個(gè)協(xié)議）協(xié)議棧：將系統(tǒng)使用的協(xié)議按層次順序（每層一個(gè)協(xié)議）列出而得到的協(xié)議列表。列出而得到的協(xié)議列表。 實(shí)通信和虛通信。實(shí)通信和虛通信。 分層網(wǎng)絡(luò)中實(shí)際的通信過(guò)程。分層網(wǎng)絡(luò)中實(shí)際的通信過(guò)

14、程。Spring10 CNWeihong Chen4.2 Design Issues for the LayersError control is an important issue because physical communication circuits are not perfect. error-detecting, error-correctingFlow control: limit the sender to an agreed-on transmission rate.Multiplexing: use the same connection for multiple,

15、unrelated conversations.Routing: When there are multiple paths between source and destination, a route must be chosen.Spring10 CNWeihong Chen4.3 Connection-Oriented and Connectionless Servicesconnection-orientedconnectionless Connection-oriented service is modeled after the telephone system. Connect

16、ionless service is modeled after the postal system.It just sends the data.Three phases: set up a connection, data transmission, release the connection.Spring10 CNWeihong ChenEach service can be characterized by a quality of service. Connection-oriented service is reliable, but Connectionless service

17、 is unreliable. Connection-oriented communication has three phases. In the establishment phase a request is made to set up a connection. Only after this phase has been successfully completed can the data transfer phase be started and data transported.Then comes the release phase. Connectionless comm

18、unication does not have these phases. It just sends the data.Spring10 CNWeihong Chen 面向連接服務(wù)面向連接服務(wù) 建立連接、傳輸數(shù)據(jù)、拆除連接三步曲。類似電話系統(tǒng)服務(wù)，建立連接、傳輸數(shù)據(jù)、拆除連接三步曲。類似電話系統(tǒng)服務(wù)，保證數(shù)據(jù)傳輸順序。保證數(shù)據(jù)傳輸順序。 無(wú)連接服務(wù)無(wú)連接服務(wù) 數(shù)據(jù)不需要沿著相同的路徑傳輸。類似郵政系統(tǒng)服務(wù)，不保證數(shù)據(jù)不需要沿著相同的路徑傳輸。類似郵政系統(tǒng)服務(wù)，不保證數(shù)據(jù)傳輸順序。數(shù)據(jù)傳輸順序。 可靠的服務(wù)可靠的服務(wù) 通過(guò)接收方的應(yīng)答來(lái)實(shí)現(xiàn)，會(huì)引入開(kāi)銷和延遲。通過(guò)接收方的應(yīng)答來(lái)實(shí)現(xiàn)，會(huì)引入開(kāi)銷

19、和延遲。Spring10 CNWeihong Chen4.5 The Relationship of Services to ProtocolsServices and protocols are distinct concepts.Fig.6 The relationship between a service and a protocolService provided by layer kProtocol A service is a set of primitives (operations) that a layer provides to the layer above it. A

20、 service relates to an interface between two layers, with the lower layer being the service provider and the upper layer being the service user. A protocol, in contrast, is a set of rules governing the format and meaning of the packets, or messages that are exchanged by the peer entities within a la

21、yer. Entities use protocols to implement their service definitions. BackSpring10 CNWeihong Chen In other words, services relate to the interfaces between layers, as illustrated in Fig. 11. In contrast, protocols relate to the packets sent between peer entities on different machines. Spring10 CNWeiho

22、ng Chen 服務(wù)服務(wù) 涉及同一系統(tǒng)的相鄰兩個(gè)層次，定義了下層可以為上層執(zhí)行的操涉及同一系統(tǒng)的相鄰兩個(gè)層次，定義了下層可以為上層執(zhí)行的操作，但沒(méi)有說(shuō)明這些操作如何完成。作，但沒(méi)有說(shuō)明這些操作如何完成。 協(xié)議協(xié)議 涉及不同系統(tǒng)上的對(duì)等實(shí)體，定義了這些實(shí)體間通信所要遵循的涉及不同系統(tǒng)上的對(duì)等實(shí)體，定義了這些實(shí)體間通信所要遵循的規(guī)則，如數(shù)據(jù)包的格式及含義等。對(duì)等實(shí)體使用協(xié)議來(lái)實(shí)現(xiàn)它們規(guī)則，如數(shù)據(jù)包的格式及含義等。對(duì)等實(shí)體使用協(xié)議來(lái)實(shí)現(xiàn)它們的服務(wù)。的服務(wù)。Spring10 CN5. Reference Models The OSI Reference Model The TCP/IP Referen

23、ce Model A Comparison of the OSI and TCP/IP Reference Models A Critique of the OSI Model and Protocols A Critique of the TCP/IP Reference ModelSpring10 CN5.1 The OSI Reference Model OSI : Open Systems Interconnection The OSI model has seven layers. Spring10 CNThe OSI Reference ModelOSI : Open System

24、s InterconnectionSpring10 CNThe Physical Layer The design issues here largely deal with mechanical, electrical, and timing interfaces, and the physical transmission medium, which lies below the physical layer. 功能：完成相鄰節(jié)點(diǎn)之間原始比特流的傳輸 協(xié)議： 機(jī)械特性：連接器形狀，DB25 電氣特性：正、負(fù)邏輯，傳輸介質(zhì)、速率、距離等 功能特性：每一根信號(hào)線的功能定義 過(guò)程特性：完成特定功

25、能時(shí)，各信號(hào)的工作過(guò)程Spring10 CNThe Data Link Layer The main task of the data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer. 功能：完成相鄰節(jié)點(diǎn)之間數(shù)據(jù)的可靠傳輸 協(xié)議： 幀(frame)結(jié)構(gòu) 差錯(cuò)控制 流量控制 LAN的數(shù)據(jù)鏈路層又分為兩個(gè)子層： 介質(zhì)訪問(wèn)子層（MAC） 邏輯鏈路子層（LLC）Spring

26、10 CNThe Network Layer A key design issue is determining how packets are routed from source to destination. 功能：完成兩個(gè)主機(jī)之間的報(bào)文的傳輸 協(xié)議：報(bào)文(packet)的格式路由選擇主機(jī)尋址擁塞控制網(wǎng)絡(luò)互聯(lián)網(wǎng)絡(luò)計(jì)費(fèi)Spring10 CNThe Transport Layer The basic function of the transport layer is to accept data from above, split it up into smaller units if n

27、eed be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.功能：在兩個(gè)主機(jī)的不同進(jìn)程之間提供無(wú)差錯(cuò)和有效的數(shù)據(jù)通信服務(wù)Spring10 CNThe Session Layer The session layer allows users on different machines to establish sessions between them. Sessions offer various services, including dia

28、log control, token management, and synchronization.The Presentation Layer The presentation layer is concerned with the syntax and semantics of the information transmitted. 功能：完成不同用戶之間的會(huì)話管理 功能：提供公共的數(shù)據(jù)表示格式或完成數(shù)據(jù)格式轉(zhuǎn)換、數(shù)據(jù)加解密以及數(shù)據(jù)壓縮和解壓縮的功能。Spring10 CNThe Application Layer The application layer contains a va

29、riety of protocols that are commonly needed by users.功能：提供訪問(wèn)網(wǎng)絡(luò)的各種接口和應(yīng)用層協(xié)議實(shí)例： E-mail，Telnet，F(xiàn)TP, WWW，BBSSpring10 CN5.2 The TCP/IP Reference ModelFig.2 The TCP/IP reference modelSpring10 CNThe Internet Layer The internet layer defines an official packet format and protocol called IP (Internet Protocol

30、). The job of the internet layer is to deliver IP packets where they are supposed to go. Packet routing is clearly the major issue here, as is avoiding congestion. For these reasons, it is reasonable to say that the TCP/IP internet layer is similar in functionality to the OSI network layer. Fig.2 sh

31、ows this correspondence.功能：負(fù)責(zé)IP報(bào)文在各節(jié)點(diǎn)中的傳輸Spring10 CNThe Transport Layer Two end-to-end transport protocols have been defined here: TCP and UDP. The first one, TCP (Transmission Control Protocol), is a reliable connection-oriented protocol that allows a byte stream originating on one machine to be de

32、livered without error on any other machine in the internet. The second protocol in this layer, UDP (User Datagram Protocol), is an unreliable, connectionless protocol for applications. The relation of IP, TCP, and UDP is shown in Fig.3 .功能：在源結(jié)點(diǎn)和目的結(jié)點(diǎn)的兩個(gè)進(jìn)程之間提供可靠的端到端的數(shù)據(jù)傳輸。Spring10 CNFig.3 Protocols and

33、 networks in the TCP/IP model initiallySpring10 CNThe Application Layer It contains all the higher-level protocols.The Host-to-Network Layer功能：提供用戶訪問(wèn)網(wǎng)絡(luò)的接口功能：接收IP協(xié)議模塊交來(lái)的IP數(shù)據(jù)報(bào)并通過(guò)物理傳輸網(wǎng)絡(luò)發(fā)送出去或者作相反的工作。Spring10 CN5.3 Comparing OSI and TCP/IP Models The OSI and TCP/IP reference models have much in common. B

34、oth are based on the concept of a stack of independent protocols. Also, the functionality of the layers is roughly similar. The two models also have many differences.Spring10 CN1. Three concepts are central to the OSI model:Services, Interfaces, Protocols The service definition tells what the layer

35、does, not how entities above it access it or how the layer works. A layers interface tells the processes above it how to access it. It specifies what the parameters are and what results to expect. It, too, says nothing about how the layer works inside. The peer protocols used in a layer are the laye

36、rs own business. It can use any protocols it wants to, as long as it gets the job done (i.e., provides the offered services). It can also change them at will without affecting software in higher layers. The TCP/IP model did not originally clearly distinguish between service, interface, and protocol.

37、Spring10 CN2. Different numbers of layers: the OSI model has seven layers and the TCP/IP has four layers. Both have (inter)network, transport, and application layers, but the other layers are different. 3. Another difference is in the area of connectionless versus connection-oriented communication.

38、The OSI model supports both connectionless and connection-oriented communication in the network layer, but only connection-oriented communication in the transport layer . The TCP/IP model has only one mode in the network layer (connectionless) but supports both modes in the transport layer .Spring10

39、 CN OSI參考模型清晰地區(qū)分服務(wù)、接口、協(xié)議三個(gè)概念，參考模型清晰地區(qū)分服務(wù)、接口、協(xié)議三個(gè)概念，而而TCP/IP參考模型沒(méi)有區(qū)分這三個(gè)概念；參考模型沒(méi)有區(qū)分這三個(gè)概念； OSI參考模型是在其協(xié)議開(kāi)發(fā)之前設(shè)計(jì)出來(lái)的，更通用參考模型是在其協(xié)議開(kāi)發(fā)之前設(shè)計(jì)出來(lái)的，更通用性；而性；而TCP/IP參考模型是對(duì)現(xiàn)成協(xié)議的描述；參考模型是對(duì)現(xiàn)成協(xié)議的描述； OSI參考模型參考模型(除去除去session和和presentation層層)可以用于可以用于很好地討論計(jì)算機(jī)網(wǎng)絡(luò)，但很好地討論計(jì)算機(jī)網(wǎng)絡(luò)，但OSI協(xié)議卻不常用；相反，協(xié)議卻不常用；相反，TCP/IP參考模型不常用，但參考模型不常用，但TCP/I

40、P協(xié)議卻很常用。協(xié)議卻很常用。Spring10 CN5.4 A Critique of the OSI Model and Protocols Why OSI did not take over the worldBad timingBad technologyBad implementationsBad politicsSpring10 CN5.5 A Critique of the TCP/IP Reference Model Problems:Service, interface, and protocol not distinguishedNot a general modelHost

41、-to-network “l(fā)ayer” not really a layerNo mention of physical and data link layersMinor protocols deeply entrenched, hard to replaceSpring10 CN In summary, despite its problems, the OSI model (minus the session and presentation layers) has proven to be exceptionally useful for discussing computer net

42、works. In contrast, the OSI protocols have not become popular. The reverse is true of TCP/IP: the model is practically nonexistent, but the protocols are widely used. In effect, the hybrid model of Fig.4 as the framework for this book.Fig.4 The hybrid reference model to be used in this bookSpring10

43、CN8 Metric UnitsM milli MicroKilo 1024 e.g. 1GB=1024Bbut, 1k bps=1000bps mSpring10 CNExercise Imagine that you have trained your St. Bernard, Bernie, to carry a box of three 8mm tapes instead of a flask of brandy. (When your disk fills up, you consider that an emergency.) These tapes each contain 7

44、gigabytes. The dog can travel to your side, wherever you may be, at 18 km/hour. For what range of distances does Bernie have a higher data rate than a transmission line whose data rate (excluding overhead) is 150 Mbps?Spring10 CNSummarize OSI Reference models TCP/IP Reference models Comparing OSI and TCP/IP ModelsSpring10 CNHomework Page82 21, 22Spring10 CNPreparation Charpter 2 The Physical LayerSpring10 CNThe answer to exercise11. What are t