4theditionchapter1

1、Introduction,1-1,Chapter 1Introduction,Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith RossAddison-WesleyMarch 2012,A note on the use of these ppt slides:We’re making these slides freely avai

2、lable to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent

3、 a lot of work on our part. In return for use, we only ask the following:,If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!)If you post any slides on

4、a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWR All material copyright 1996-2012 J.F Kurose and K

5、.W. Ross, All Rights Reserved,Chapter 1: Introduction,Our goal: get “feel” and terminologymore depth, detail later in courseapproach:use Internet as example,Introduction,1-2,計(jì)算機(jī)網(wǎng)絡(luò)向用戶(hù)提供的最重要的功能,連通性——計(jì)算機(jī)網(wǎng)絡(luò)使上網(wǎng)用戶(hù)之間都可以交換信

6、息，好像這些用戶(hù)的計(jì)算機(jī)都可以彼此直接連通一樣。 共享——即資源共享?？梢允切畔⒐蚕?、軟件共享，也可以是硬件共享。,世界十大互連網(wǎng)公司(2014),谷歌、臉譜、阿里巴巴、亞馬遜、騰迅、百度、ebay、Priceline、雅虎和京東(2014.9)：,世界六大互連網(wǎng)公司(2017),2017年，全球互聯(lián)網(wǎng)公司市值排名前六位分別是蘋(píng)果、谷歌、亞馬遜、Facebook、騰訊和阿里巴巴。放眼全球公司市值，互聯(lián)網(wǎng)公司占據(jù)了前五名：,中國(guó)十大互連

7、網(wǎng)公司,騰訊、阿里巴巴、百度、京東、網(wǎng)易、新浪、美團(tuán)點(diǎn)評(píng)、攜程、360。其中，騰訊、阿里巴巴、百度連續(xù)五年位居前三。(2017.8),BAT,分別是B百度、A阿里巴巴、T騰訊的首字母,李克強(qiáng)與互連網(wǎng)+,2015年政府工作報(bào)告：“制定‘互聯(lián)網(wǎng)+’行動(dòng)計(jì)劃，推動(dòng)移動(dòng)互聯(lián)網(wǎng)、云計(jì)算、大數(shù)據(jù)、物聯(lián)網(wǎng)等與現(xiàn)代制造業(yè)結(jié)合，促進(jìn)電子商務(wù)、工業(yè)互聯(lián)網(wǎng)和互聯(lián)網(wǎng)金融健康發(fā)展，引導(dǎo)互聯(lián)網(wǎng)企業(yè)拓展國(guó)際市場(chǎng)?！?互連網(wǎng)+,互聯(lián)網(wǎng)+XX傳統(tǒng)行業(yè)=互聯(lián)網(wǎng)XX行業(yè)

8、利用信息通信技術(shù)以及互聯(lián)網(wǎng)平臺(tái)，讓互聯(lián)網(wǎng)與傳統(tǒng)行業(yè)進(jìn)行深度融合，創(chuàng)造新的發(fā)展生態(tài)。電子商務(wù)、互聯(lián)網(wǎng)金融、在線旅游、在線影視、在線房產(chǎn)等行業(yè)都是“互聯(lián)網(wǎng)+”的杰作。,十三五“網(wǎng)絡(luò)強(qiáng)國(guó)戰(zhàn)略”,構(gòu)建泛在高效的信息網(wǎng)絡(luò)：加快構(gòu)建高速、移動(dòng)、安全、泛在的新一代信息基礎(chǔ)設(shè)施，推進(jìn)信息網(wǎng)絡(luò)技術(shù)廣泛運(yùn)用，形成萬(wàn)物互聯(lián)、人機(jī)交互、天地一體的網(wǎng)絡(luò)空間 發(fā)展現(xiàn)代互聯(lián)網(wǎng)產(chǎn)業(yè)體系：實(shí)施“互聯(lián)網(wǎng)+”行動(dòng)計(jì)劃，促進(jìn)互聯(lián)網(wǎng)深度廣泛應(yīng)用，帶動(dòng)生產(chǎn)模式和組

9、織方式變革，形成網(wǎng)絡(luò)化、智能化、服務(wù)化、協(xié)同化的產(chǎn)業(yè)發(fā)展新形態(tài),國(guó)家信息化發(fā)展戰(zhàn)略綱要(2016.7),中國(guó)信息化戰(zhàn)略：2025年核心技術(shù)不受制于人到2020年3G、4G網(wǎng)絡(luò)要覆蓋中國(guó)城鄉(xiāng)，5G技術(shù)研發(fā)和標(biāo)準(zhǔn)要取得突破性進(jìn)展；信息消費(fèi)總額要達(dá)到6萬(wàn)億元(人民幣，下同)，電子商務(wù)交易規(guī)模達(dá)到38萬(wàn)億元；核心關(guān)鍵技術(shù)部分領(lǐng)域要達(dá)到國(guó)際先進(jìn)水平；建成中國(guó)-東盟信息港，初步建成網(wǎng)上絲綢之路。 到2025年，要實(shí)現(xiàn)寬帶網(wǎng)絡(luò)無(wú)縫覆蓋；信息消費(fèi)總

10、額達(dá)到12萬(wàn)億元，電子商務(wù)交易規(guī)模達(dá)到67萬(wàn)億元；根本改變核心關(guān)鍵技術(shù)受制于人的局面。,國(guó)家信息化發(fā)展戰(zhàn)略綱要(2016.7),屆時(shí)，中國(guó)還計(jì)劃建成四大國(guó)際信息通道，連接太平洋、中東歐、西非北非、東南亞、中亞、印巴緬俄等國(guó)家和地區(qū)，涌現(xiàn)一批具有強(qiáng)大國(guó)際競(jìng)爭(zhēng)力的大型跨國(guó)網(wǎng)信企業(yè)。到本世紀(jì)中葉，中國(guó)網(wǎng)絡(luò)強(qiáng)國(guó)地位要日益鞏固，在引領(lǐng)全球信息化發(fā)展方面有更大作為。,計(jì)算機(jī)和人類(lèi)潛力將是推動(dòng)經(jīng)濟(jì)增長(zhǎng)的主力,18世紀(jì)以前，經(jīng)濟(jì)的驅(qū)動(dòng)力為農(nóng)耕19

11、世紀(jì)至20世紀(jì)，制造和工業(yè)成為經(jīng)濟(jì)發(fā)展的主力進(jìn)入21世紀(jì)，計(jì)算機(jī)和人類(lèi)潛力將是推動(dòng)經(jīng)濟(jì)增長(zhǎng)的主力。,Introduction,1-15,什么是網(wǎng)絡(luò) --- 從端系統(tǒng)的角度看(1),網(wǎng)絡(luò)提供的服務(wù): 信息傳遞信鴿、烽火、信使 、卡車(chē)、電報(bào)、電話(huà)、Internet…,什么是網(wǎng)絡(luò) --- 從端系統(tǒng)的角度看(2),不同的網(wǎng)絡(luò)以什么為區(qū)分所提供的服務(wù)服務(wù)以什么為區(qū)分延遲、帶寬、丟失率、端節(jié)點(diǎn)數(shù)目、服務(wù)接口、可靠性, 單播/多播，實(shí)時(shí)

12、，消息/字節(jié)流,什么是網(wǎng)絡(luò) --- 從網(wǎng)絡(luò)核心的角度看,電子、光子等作為傳輸介質(zhì)鏈路：光纖、電纜和衛(wèi)星交換節(jié)點(diǎn)：機(jī)械/電/光協(xié)議: TCP/IP, ATM, MPLS, SONET, Ethernet, PPP, X.25, FrameRelay, AppleTalk, IPX, SNA功能: 路由，差錯(cuò)控制、擁塞控制、服務(wù)質(zhì)量(QoS)應(yīng)用：FTP、HTTP、X windows,Introduction,1-19,Chapt

13、er 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched net

14、works1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,概述,1-20,1.1.1 具體構(gòu)成描述,終端設(shè)備：稱(chēng) 主機(jī)（host）或端系統(tǒng)（ end system） 運(yùn)行網(wǎng)絡(luò)應(yīng)用程序,通信鏈路：光纖，銅線，射頻等傳輸速率常稱(chēng)為帶寬（bandwidth）,分組交換機(jī): 轉(zhuǎn)發(fā)分組（packet）路由器和鏈路層

15、交換機(jī),具體構(gòu)成描述,路由（route, path）：分組從發(fā)送終端到接收終端經(jīng)過(guò)的通信鏈路及分組交換機(jī)的序列。Internet Service Provider（ISP）：由分組交換機(jī)和通信鏈路組成的網(wǎng)絡(luò)為終端提供接入因特網(wǎng)的服務(wù),Introduction,1-22,具體構(gòu)成描述,協(xié)議規(guī)定了設(shè)備之間通信的規(guī)則： 如 TCP, IP, HTTP, Skype因特網(wǎng)標(biāo)準(zhǔn)：以RFC（Request for comments

16、）文檔的形式發(fā)布由IETF（ Internet Engineering Task Force）組織統(tǒng)一管理,具體構(gòu)成描述,因特網(wǎng)是“網(wǎng)絡(luò)的網(wǎng)絡(luò)”:按松散的層次結(jié)構(gòu)組織、并且遵循TCP/IP協(xié)議的ISP集合。（描述一）,Introduction,1-24,1.1.2 服務(wù)描述,因特網(wǎng)是為分布式應(yīng)用提供通信服務(wù)的基礎(chǔ)設(shè)施：（描述二）應(yīng)用程序運(yùn)行在端系統(tǒng)上端系統(tǒng)為應(yīng)用程序提供使用因特網(wǎng)服務(wù)的API因特網(wǎng)提供的通信服務(wù)包括：源主機(jī)

17、到目的主機(jī)的可靠數(shù)據(jù)交付盡力而為的（不可靠的）數(shù)據(jù)交付,Introduction,1-25,1.1.3 什么是協(xié)議,一個(gè)人類(lèi)協(xié)議 一個(gè)計(jì)算機(jī)網(wǎng)絡(luò)協(xié)議,,Hi,,Hi,,,TCP connection request,,,,,,1-26,網(wǎng)絡(luò)協(xié)議,human protocols:specific msgs sentspecific actions taken when msgs rec

18、eived, or other events,network protocols:machines rather than humansall communication activity in Internet governed by protocols,協(xié)議定義了通信實(shí)體之間交換的報(bào)文的格式和次序，以及在報(bào)文發(fā)送、接收或收到其它事件后采取的動(dòng)作。掌握計(jì)算機(jī)網(wǎng)絡(luò)知識(shí)的過(guò)程，就是理解網(wǎng)絡(luò)協(xié)議構(gòu)成、原理和工作的過(guò)程。,Introdu

19、ction,1-27,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in pac

20、ket-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-28,A closer look at network structure:,end systems: 終端,access networks：將終端連接到其邊緣路由器的物理鏈路,networ

21、k core: 路由器和通信鏈路組成的網(wǎng)狀網(wǎng)絡(luò),Introduction,1-29,1.2.1 接入網(wǎng),Q: How to connect end systems to edge router?住宅接入公司接入（學(xué)校，公司）移動(dòng)接入Keep in mind: 接入網(wǎng)的帶寬（bits per second) 是多少？共享還是專(zhuān)用？,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

22、,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Introduction,家庭接入: 數(shù)字用戶(hù)線（DSL）,,,,,,,

23、central office,,telephonenetwork,DSLAM,,,,使用已有的數(shù)字電話(huà)線：數(shù)據(jù)送往因特網(wǎng)聲音送往電話(huà)網(wǎng)上行速率< 2.5 Mbps (典型地 < 1 Mbps)下行速率< 24 Mbps (典型地 < 10 Mbps),,,DSLmodem,splitter,,,,,,,1-30,Introduction,家庭接入: cable network,,,cablemode

24、m,splitter,,,,,,…,,,,,,,cable headend,,,,,,,,頻分復(fù)用: 將電纜劃分成不相重疊的頻段，每個(gè)頻段傳輸一路信號(hào),,1-31,Introduction,,,cablemodem,splitter,,,,,,…,,,,,,,cable headend,,,,,,,CMTS,,,混合光纖同軸電纜HFC: hybrid fiber coax下行速率最高 30Mbps上行速率最高 2 Mbps光纖、

25、電纜、cable modem、CMTS構(gòu)成接入網(wǎng)從住宅到電纜頭端的接入網(wǎng)部分是共享的,家庭接入: cable network,,1-32,Introduction,企業(yè)（和家庭）接入：Ethernet,主要用于公司、學(xué)校等傳輸速率：10 Mbps, 100Mbps, 1Gbps, 10Gbps以太網(wǎng)交換機(jī)及鏈路構(gòu)成接入網(wǎng),,,,,,,,,,Ethernet switch,,institutional mail,web serv

26、ers,institutional router,,,,,institutional link to ISP (Internet),,,,,,,1-33,Introduction,1-34,企業(yè)（和家庭）接入：無(wú)線局域網(wǎng),公司或個(gè)人提供基站（接入點(diǎn)），主要將移動(dòng)終端連接到有線網(wǎng)絡(luò)：終端與基站相距幾十米內(nèi)基站通常位于有線網(wǎng)絡(luò)上傳輸速率（Wifi）：11 or 54Mbps無(wú)線局域網(wǎng)是共享的,,,,,,,basestation,

27、mobilehosts,,router,Introduction,一個(gè)典型的家庭網(wǎng)絡(luò),,to/from headend or central office,,,,wirelessdevices,,,,,1-35,Introduction,廣域無(wú)線接入：3G/4G,由電信公司提供，使用現(xiàn)有的蜂窩電話(huà)網(wǎng)絡(luò)基站可為數(shù)萬(wàn)米半徑內(nèi)的用戶(hù)提供無(wú)線接入服務(wù)傳輸速率：3G：最大（靜止）2Mbps4G：下行100Mbps，上行20Mbps,t

28、o Internet,1-36,Introduction,1-37,1.2.2 物理媒體,設(shè)備之間通過(guò)物理媒體相連在一條路徑上，每對(duì)設(shè)備之間的物理媒體可以不同導(dǎo)引型媒體: 信號(hào)沿固體媒體傳播，如銅線，光纖非導(dǎo)引型媒體: 信號(hào)在空間自由傳播，如無(wú)線電,雙絞線：兩條絕緣的銅導(dǎo)線：3類(lèi)線: 10 Mbps5類(lèi)線: 100Mbps~1Gbps6類(lèi)線：10Gbps,Introduction,1-38,同軸電纜，光纖,同軸電纜:

29、兩根同心的絕緣銅導(dǎo)體基帶同軸電纜:single channel on cablelegacy Ethernet寬帶同軸電纜 multiple channels on cable HFC,光纖:能引導(dǎo)光脈沖的玻璃纖維，每個(gè)脈沖傳輸一比特。點(diǎn)-點(diǎn)傳輸速率:數(shù)十甚至數(shù)百Gb/s低誤碼率: 長(zhǎng)距離傳輸; 抗電磁干擾,Introduction,1-39,射頻（radio）,電磁信號(hào)影響傳輸速率的因素:距離：路徑損耗環(huán)境

30、：多徑衰落（信號(hào)反射） 遮擋衰落（障礙物）干擾,射頻鏈路類(lèi)型:短距離：如藍(lán)牙局域：如Wifi廣域：如3G衛(wèi)星280ms端到端延遲同步衛(wèi)星，近地軌道衛(wèi)星,Introduction,1-40,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core

31、circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-41,網(wǎng)絡(luò)核心

32、,由路由器和通信鏈路形成的網(wǎng)狀網(wǎng)絡(luò)任務(wù)：將數(shù)據(jù)從發(fā)送終端的邊緣路由器傳輸?shù)浇邮战K端的邊緣路由器基本問(wèn)題: 數(shù)據(jù)如何在網(wǎng)絡(luò)中傳遞?電路交換分組交換,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Introduction,主機(jī)將應(yīng)用報(bào)文劃分成分組在從源終端到目的終端的路

33、徑上，分組從一個(gè)設(shè)備發(fā)送到下一個(gè)設(shè)備交換機(jī)僅在接收到整個(gè)分組后，才可以開(kāi)始轉(zhuǎn)發(fā)（存儲(chǔ)-轉(zhuǎn)發(fā)）,1.3.1 分組交換（packet switching）,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1-42,Introduction,存儲(chǔ)轉(zhuǎn)發(fā)引入延遲,假設(shè)分組長(zhǎng)度為L(zhǎng)比特，鏈路速率為R b/s將一個(gè)分組全部推送到一條鏈路上，耗時(shí) L/R 秒將一個(gè)分組從源發(fā)送到目的，總耗時(shí) = 2 L/R （不考慮信號(hào)傳

34、播時(shí)間）,3個(gè)分組從源終端發(fā)送到目的終端，總耗時(shí)=？4 L/R問(wèn)題：P個(gè)分組經(jīng)過(guò)N條鏈路的總耗時(shí)是多少？（P+N-1）L/R,1-43,source,,,R bps,,destination,1,2,3,L bitsper packet,R bps,,Introduction,排隊(duì)延時(shí)和分組丟失,,,,,,,,,,,,,,,,,,,A,B,C,R = 100 Mb/s,R = 1.5 Mb/s,,,,D,E,queue of

35、packetswaiting for output link,,,,,,1-44,排隊(duì)和丟包: 當(dāng)分組到達(dá)速率大于鏈路輸出速率時(shí):分組在對(duì)應(yīng)鏈路的輸出緩存中排隊(duì)，等待被發(fā)送到鏈路上，產(chǎn)生排隊(duì)延遲 若鏈路的輸出緩存滿(mǎn)，分組被丟棄，產(chǎn)生丟包,Network Layer,1-45,網(wǎng)絡(luò)核心的兩個(gè)重要功能,轉(zhuǎn)發(fā)（forwarding）: 按照轉(zhuǎn)發(fā)表，將分組從輸入鏈路移動(dòng)到輸出鏈路,選路(routing): 確定分組所走的路徑，生成轉(zhuǎn)

36、發(fā)表,,分組交換網(wǎng)絡(luò)原理總結(jié),存儲(chǔ)轉(zhuǎn)發(fā)動(dòng)態(tài)路由(包括每個(gè)分組自帶源地址、目的地址，拓?fù)浒l(fā)現(xiàn)、路由選擇)出錯(cuò)交由端系統(tǒng)處理,Introduction,1.3.2 電路交換（circuit switching）,電話(huà)網(wǎng)采用電路交換通信前預(yù)留好端-端資源（對(duì)比：分組交換不預(yù)留資源）資源獨(dú)占：保證性能（帶寬，延遲）在通信的靜默期，資源被閑置,1-47,Introduction,1-48,頻分復(fù)用FDM ，時(shí)分復(fù)用TDM,,,,,In

37、troduction,1-49,Numerical example,How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?All links are 1.536 MbpsEach link uses TDM with 24 slots/sec500 msec to esta

38、blish end-to-end circuitLet’s work it out!,Introduction,1-50,分組交換 vs 電路交換,1 Mb/s linkeach user: 100 kb/s when “active”active 10% of time電路交換（固定分配）10 users分組交換（按需分配）with 35 users, probability > 10 active at sa

39、me time is less than .0004,分組交換允許更多用戶(hù)使用網(wǎng)絡(luò)!,,,,,N users,1 Mbps link,,Introduction,1-51,時(shí)分復(fù)用 vs 統(tǒng)計(jì)復(fù)用,Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand ? statistical multiplexing.TDM: 每個(gè)

40、終端在周而復(fù)始的TDM幀中占有固定的時(shí)隙.,,,,,,,,,,,,,,,,,,,,,,,,,,,,A,B,C,100 Mb/sEthernet,1.5 Mb/s,,,,,statistical multiplexing,queue of packetswaiting for outputlink,,Introduction,1-52,分組交換 vs 電路交換,適合突發(fā)數(shù)據(jù)簡(jiǎn)單，不需建立電路可能產(chǎn)生嚴(yán)重?fù)砣? 延遲，丟包需要有

41、保證可靠傳輸和擁塞控制的協(xié)議Q: How to provide circuit-like behavior?音/視頻應(yīng)用需要保證帶寬至今未解決的問(wèn)題 (chapter 7),Is packet switching a “slam dunk winner?”,1.3.3 網(wǎng)絡(luò)的網(wǎng)絡(luò),端系統(tǒng)通過(guò)一個(gè)接入ISP與因特網(wǎng)相連接入ISP必須相互連接 受經(jīng)濟(jì)因素和國(guó)家政策的影響，因特網(wǎng)的結(jié)構(gòu)非常復(fù)雜,網(wǎng)絡(luò)的網(wǎng)絡(luò),Question: g

42、iven millions of access ISPs, how to connect them together?,網(wǎng)絡(luò)的網(wǎng)絡(luò)：樸素的方法,Option: connect each access ISP to every other access ISP?,connecting each access ISP to each other directly doesn’t scale: O(N2) connections.,網(wǎng)絡(luò)的網(wǎng)絡(luò)

43、：?jiǎn)我坏娜騃SP,Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement.,,globalISP,網(wǎng)絡(luò)的網(wǎng)絡(luò)：多個(gè)全球ISP,But if one global ISP is viable business, there will be competitors ….,網(wǎng)絡(luò)的網(wǎng)

44、絡(luò)：多個(gè)全球ISP,But if one global ISP is viable business, there will be competitors …. which must be interconnected,peering link,Internet exchange point,網(wǎng)絡(luò)的網(wǎng)絡(luò)：多層結(jié)構(gòu),… and regional networks may arise to connect access nets to I

45、SPS,,regional net,,因特網(wǎng)生態(tài)系統(tǒng),接入ISP區(qū)域ISP第一層ISP存在點(diǎn)PoP：低層ISP接入高層ISP的地方多宿：一個(gè)ISP可以與兩個(gè)或多個(gè)上層ISP連接對(duì)等：相同層次上的一對(duì)ISP直接相連，不進(jìn)行結(jié)算因特網(wǎng)交換點(diǎn)IXP：多個(gè)ISP在這里共同對(duì)等,網(wǎng)絡(luò)的網(wǎng)絡(luò)：內(nèi)容提供商網(wǎng)絡(luò),… and content provider networks (e.g., Google, Microsoft, Akam

46、ai ) may run their own network, to bring services, content close to end users,,regional net,,,Content provider network,Introduction,網(wǎng)絡(luò)的網(wǎng)絡(luò)：今天的因特網(wǎng)結(jié)構(gòu),at center: small # of well-connected large networks“tier-1” commercial I

47、SPs ：national & international coveragecontent provider network : private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs,1-62,Introduction,1-63,Chapter 1: roadmap,1.1 What is

48、 the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers

49、, service models1.6 Networks under attack: security1.7 History,Introduction,1-64,分組延遲的來(lái)源,1. 節(jié)點(diǎn)處理: 檢查比特錯(cuò)誤確定輸出鏈路,2. 排隊(duì)在輸出緩存等待傳輸 時(shí)間長(zhǎng)短取決于鏈路擁塞程度,Introduction,1-65,分組延遲的來(lái)源,3. 傳輸延遲:R=link bandwidth (bps)L=packet length

50、(bits)將分組發(fā)送到鏈路上的時(shí)間 = L/R,4. 傳播延遲:d = length of physical links = propagation speed in medium (~2x108 m/sec)propagation delay = d/s,Note: s and R are very different quantities!,,Introduction,1-66,節(jié)點(diǎn)延遲,dproc = 處理延遲典型地為

51、幾個(gè)微秒或更低dqueue = 排隊(duì)延遲取決于擁塞程度dtrans = 傳輸延遲微秒～毫秒, 低速鏈路上較大dprop = 傳播延遲幾微秒～幾百毫秒，長(zhǎng)距離鏈路上較大,Introduction,1-67,排隊(duì)延遲與流量強(qiáng)度,R=link bandwidth (bps)L=packet length (bits)a=average packet arrival rate,traffic intensity = La/R,L

52、a/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced, average delay infinite!,Introduction,1-68,排隊(duì)與丟包,輸出隊(duì)列的容量是有限的隊(duì)列滿(mǎn)時(shí)，新到達(dá)的分組被丟棄,,,,,,,,,,,,,,,A,B

53、,packet being transmitted,,,,,,,,,packet arriving tofull buffer is lost,buffer (waiting area),,Introduction,1-69,,端到端吞吐量,發(fā)送端和接收端之間的比特傳輸速率：瞬時(shí)吞吐量: 給定時(shí)刻的傳輸速度平均吞吐量: 較長(zhǎng)時(shí)間內(nèi)的傳輸速度,server, withfile of F bits to send to clie

54、nt,,link capacity Rs bits/sec,link capacity Rc bits/sec,,,,,,,server sends bits (fluid) into pipe,Introduction,1-70,吞吐量 (more),Rs < Rc What is average end-end throughput?,,,Rs bits/sec,,,,Introduction,1-71,Through

55、put: Internet scenario,10 connections (fairly) share backbone bottleneck link R bits/sec,,,,,,,,,,Rs,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Rs,Rs,,Rc,,,Rc,Rc,R,端到端吞吐量: min(Rc,Rs,R/10)吞吐量與鏈路速率及鏈路上的負(fù)載有關(guān),Introd

56、uction,1-72,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in pa

57、cket-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-73,Protocol “Layers”,Networks are complex! many “pieces”:hostsrouterslinks of various mediaap

58、plicationsprotocolshardware, software,Question: Is there any hope of organizing structure of network?Or at least our discussion of networks?,Introduction,1-74,Organization of air travel,a series of steps,Introductio

59、n,1-75,Layering of airline functionality,分層：將系統(tǒng)功能組織成一系列水平的層次，每層實(shí)現(xiàn)一個(gè)功能（服務(wù)）每層通過(guò)以下方式提供它的服務(wù)：在本層內(nèi)執(zhí)行一些動(dòng)作依靠下層提供的服務(wù),Introduction,1-76,為什么分層?,易于處理復(fù)雜系統(tǒng):顯式的層次結(jié)構(gòu)易于確定系統(tǒng)的各個(gè)部分及其相互關(guān)系模塊化簡(jiǎn)化了系統(tǒng)的維護(hù)和升級(jí)改變某層服務(wù)的實(shí)現(xiàn)對(duì)于其它層次是透明的,Introduction,1

60、-77,,Internet協(xié)議棧,application: 支持各種網(wǎng)絡(luò)應(yīng)用E.g., FTP, SMTP, HTTPtransport: 進(jìn)程-進(jìn)程的分組傳輸TCP, UDPnetwork: 源主機(jī)-目的主機(jī)的分組傳輸IP, routing protocolslink: 相鄰網(wǎng)絡(luò)設(shè)備之間的分組傳輸E.g., PPP, Ethernetphysical: 在物理媒體上傳輸比特,Introduction,1-78,,ISO

61、/OSI reference model,presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventionssession: synchronization, checkpointing, recovery of data exchangeInternet

62、stack “missing” these layers!these services, if needed, must be implemented in applicationneeded?,Introduction,1-79,,,source,,,,,applicationtransportnetworklinkphysical,,,,segment,datagram,destination,,,,,applicati

63、ontransportnetworklinkphysical,,,,,,router,switch,封裝,message,frame,Introduction,1-80,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switch

64、ing, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-81,Chapter 1: roadmap

65、,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Pro

66、tocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-82,Internet History,1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in

67、military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational,1972: ARPAnet public demonstrationNCP (Network Control Protocol) first host-host protocol first e-mail pr

68、ogramARPAnet has 15 nodes,1961-1972: Early packet-switching principles,Introduction,1-83,Internet History,1970: ALOHAnet satellite network in Hawaii1974: Cerf and Kahn - architecture for interconnecting networks1976: