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:Were making these slides freely available to all (faculty, students, readers). Theyre in PowerPoint form so you see the ani
2、mations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent 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, wed like p
3、eople to use our book!)If you post any slides on 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.W. Ross, All Rights Reserved,Chapter 1: Intr
4、oduction,Our goal: get “feel” and terminologymore depth, detail later in courseapproach:use Internet as example,Introduction,1-2,计算机网络向用户提供的最重要的功能,连通性计算机网络使上网用户之间都可以交换信息，好像这些用户的计算机都可以彼此直接连通一样。 共享即资源共享。可以是信息共享、软件共享，也可以是硬件共享。,世界十大互连网公司(2014),谷歌、脸谱、阿里巴巴、亚马逊、腾迅、百度、ebay、Priceline、雅虎和京东(2014.9)：,世界六大互连网公司
5、(2017),2017年，全球互联网公司市值排名前六位分别是苹果、谷歌、亚马逊、Facebook、腾讯和阿里巴巴。放眼全球公司市值，互联网公司占据了前五名：,中国十大互连网公司,腾讯、阿里巴巴、百度、京东、网易、新浪、美团点评、携程、360。其中，腾讯、阿里巴巴、百度连续五年位居前三。(2017.8),BAT,分别是B百度、A阿里巴巴、T腾讯的首字母,李克强与互连网+,2015年政府工作报告：“制定互联网+行动计划，推动移动互联网、云计算、大数据、物联网等与现代制造业结合，促进电子商务、工业互联网和互联网金融健康发展，引导互联网企业拓展国际市场。”,互连网+,互联网+XX传统行业=互联网XX行
6、业利用信息通信技术以及互联网平台，让互联网与传统行业进行深度融合，创造新的发展生态。电子商务、互联网金融、在线旅游、在线影视、在线房产等行业都是“互联网+”的杰作。,十三五“网络强国战略”,构建泛在高效的信息网络：加快构建高速、移动、安全、泛在的新一代信息基础设施，推进信息网络技术广泛运用，形成万物互联、人机交互、天地一体的网络空间 发展现代互联网产业体系：实施“互联网+”行动计划，促进互联网深度广泛应用，带动生产模式和组织方式变革，形成网络化、智能化、服务化、协同化的产业发展新形态,国家信息化发展战略纲要(2016.7),中国信息化战略：2025年核心技术不受制于人到2020年3G、4G网络
7、要覆盖中国城乡，5G技术研发和标准要取得突破性进展；信息消费总额要达到6万亿元(人民币，下同)，电子商务交易规模达到38万亿元；核心关键技术部分领域要达到国际先进水平；建成中国-东盟信息港，初步建成网上丝绸之路。 到2025年，要实现宽带网络无缝覆盖；信息消费总额达到12万亿元，电子商务交易规模达到67万亿元；根本改变核心关键技术受制于人的局面。,国家信息化发展战略纲要(2016.7),届时，中国还计划建成四大国际信息通道，连接太平洋、中东欧、西非北非、东南亚、中亚、印巴缅俄等国家和地区，涌现一批具有强大国际竞争力的大型跨国网信企业。到本世纪中叶，中国网络强国地位要日益巩固，在引领全球信息化发
8、展方面有更大作为。,计算机和人类潜力将是推动经济增长的主力,18世纪以前，经济的驱动力为农耕19世纪至20世纪，制造和工业成为经济发展的主力进入21世纪，计算机和人类潜力将是推动经济增长的主力。,Introduction,1-15,什么是网络 - 从端系统的角度看(1),网络提供的服务: 信息传递信鸽、烽火、信使 、卡车、电报、电话、Internet,什么是网络 - 从端系统的角度看(2),不同的网络以什么为区分所提供的服务服务以什么为区分延迟、带宽、丢失率、端节点数目、服务接口、可靠性, 单播/多播，实时，消息/字节流,什么是网络 - 从网络核心的角度看,电子、光子等作为传输介质链路：光纤、
9、电缆和卫星交换节点：机械/电/光协议: TCP/IP, ATM, MPLS, SONET, Ethernet, PPP, X.25, FrameRelay, AppleTalk, IPX, SNA功能: 路由，差错控制、拥塞控制、服务质量(QoS)应用：FTP、HTTP、X windows,Introduction,1-19,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, pack
10、et switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,概述,1-20,1.1.1 具体构成描述,终端设备：称 主机（host）或端系统（ end system） 运行网络应用程序,通信链路：光纤，铜线，射频等传输速率常称为带宽（bandwidth）,分组交换机: 转发分组（packet）路由器和链路层交换机,具
11、体构成描述,路由（route, path）：分组从发送终端到接收终端经过的通信链路及分组交换机的序列。Internet Service Provider（ISP）：由分组交换机和通信链路组成的网络为终端提供接入因特网的服务,Introduction,1-22,具体构成描述,协议规定了设备之间通信的规则： 如 TCP, IP, HTTP, Skype因特网标准：以RFC（Request for comments）文档的形式发布由IETF（ Internet Engineering Task Force）组织统一管理,具体构成描述,因特网是“网络的网络”:按松散的层次结构组织、并且遵循TCP/IP
12、协议的ISP集合。（描述一）,Introduction,1-24,1.1.2 服务描述,因特网是为分布式应用提供通信服务的基础设施：（描述二）应用程序运行在端系统上端系统为应用程序提供使用因特网服务的API因特网提供的通信服务包括：源主机到目的主机的可靠数据交付尽力而为的（不可靠的）数据交付,Introduction,1-25,1.1.3 什么是协议,一个人类协议 一个计算机网络协议,Hi,Hi,TCP connection request,1-26,网络协议,human protocols:specific msgs sentspecific actions taken when msgs
13、received, or other events,network protocols:machines rather than humansall communication activity in Internet governed by protocols,协议定义了通信实体之间交换的报文的格式和次序，以及在报文发送、接收或收到其它事件后采取的动作。掌握计算机网络知识的过程，就是理解网络协议构成、原理和工作的过程。,Introduction,1-27,Chapter 1: roadmap,1.1 What is the Internet?1.2 Network edge end syst
14、ems, access networks, links1.3 Network core 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,1-28,A closer look at network structure:,end syst
15、ems: 终端,access networks：将终端连接到其边缘路由器的物理链路,network core: 路由器和通信链路组成的网状网络,Introduction,1-29,1.2.1 接入网,Q: How to connect end systems to edge router?住宅接入公司接入（学校，公司）移动接入Keep in mind: 接入网的带宽（bits per second) 是多少？共享还是专用？,Introduction,家庭接入: 数字用户线（DSL）,central office,telephonenetwork,DSLAM,使用已有的数字电话线：数据送往因特网
16、声音送往电话网上行速率 2.5 Mbps (典型地 1 Mbps)下行速率 24 Mbps (典型地 10 active at same time is less than .0004,分组交换允许更多用户使用网络!,N users,1 Mbps link,Introduction,1-51,时分复用 vs 统计复用,Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing.TDM: 每个终端在周而复始的TDM帧中占有固定的时隙.,A,B,
17、C,100 Mb/sEthernet,1.5 Mb/s,statistical multiplexing,queue of packetswaiting for outputlink,Introduction,1-52,分组交换 vs 电路交换,适合突发数据简单，不需建立电路可能产生严重拥塞: 延迟，丢包需要有保证可靠传输和拥塞控制的协议Q: How to provide circuit-like behavior?音/视频应用需要保证带宽至今未解决的问题 (chapter 7),Is packet switching a “slam dunk winner?”,1.3.3 网络的网络,端系统
18、通过一个接入ISP与因特网相连接入ISP必须相互连接 受经济因素和国家政策的影响，因特网的结构非常复杂,网络的网络,Question: given millions of access ISPs, how to connect them together?,网络的网络：朴素的方法,Option: connect each access ISP to every other access ISP?,connecting each access ISP to each other directly doesnt scale: O(N2) connections.,网络的网络：单一的全球ISP,Op
19、tion: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement.,globalISP,网络的网络：多个全球ISP,But if one global ISP is viable business, there will be competitors .,网络的网络：多个全球ISP,But if one global ISP is viable business, there will be competitors . which must be i
20、nterconnected,peering link,Internet exchange point,网络的网络：多层结构, and regional networks may arise to connect access nets to ISPS,regional net,因特网生态系统,接入ISP区域ISP第一层ISP存在点PoP：低层ISP接入高层ISP的地方多宿：一个ISP可以与两个或多个上层ISP连接对等：相同层次上的一对ISP直接相连，不进行结算因特网交换点IXP：多个ISP在这里共同对等,网络的网络：内容提供商网络, and content provider networks
21、(e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users,regional net,Content provider network,Introduction,网络的网络：今天的因特网结构,at center: small # of well-connected large networks“tier-1” commercial ISPs ：national & international coveragecontent provider
22、 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 the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.
23、4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-64,分组延迟的来源,1. 节点处理: 检查比特错误确定输出链路,2. 排队在输出缓存等待传输 时间长短取决于链路拥塞程度,Introduction,1-65,分组延迟的来源,3. 传输延迟:R=link bandwidth (bps)L=packet length (bits)将分组发送到链
24、路上的时间 = L/R,4. 传播延迟: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,节点延迟,dproc = 处理延迟典型地为几个微秒或更低dqueue = 排队延迟取决于拥塞程度dtrans = 传输延迟微秒毫秒, 低速链路上较大dprop = 传播延迟几微秒几百毫秒，长距离链路上较大,Introduction,1-67,
25、排队延迟与流量强度,R=link bandwidth (bps)L=packet length (bits)a=average packet arrival rate,traffic intensity = La/R,La/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,排队与丢包,输出队列的容量是有限的队列满时，新到达的分组被丢弃,A
26、,B,packet being transmitted,packet arriving tofull buffer is lost,buffer (waiting area),Introduction,1-69,端到端吞吐量,发送端和接收端之间的比特传输速率：瞬时吞吐量: 给定时刻的传输速度平均吞吐量: 较长时间内的传输速度,server, withfile of F bits to send to client,link capacity Rs bits/sec,link capacity Rc bits/sec,server sends bits (fluid) into pipe,Int
27、roduction,1-70,吞吐量 (more),Rs Rc What is average end-end throughput?,Rs bits/sec,Introduction,1-71,Throughput: 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)吞吐量与链路速率及链路上的负载有关,Introduction,1-72,Chapter 1: roadmap,1.1 What
28、 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 Protocol layers, service models1.6 Networks under attack: security1.7 History,Introduction,1-73,Pr
29、otocol “Layers”,Networks are complex! many “pieces”:hostsrouterslinks of various mediaapplicationsprotocolshardware, 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,Introduc
30、tion,1-75,Layering of airline functionality,分层：将系统功能组织成一系列水平的层次，每层实现一个功能（服务）每层通过以下方式提供它的服务：在本层内执行一些动作依靠下层提供的服务,Introduction,1-76,为什么分层?,易于处理复杂系统:显式的层次结构易于确定系统的各个部分及其相互关系模块化简化了系统的维护和升级改变某层服务的实现对于其它层次是透明的,Introduction,1-77,Internet协议栈,application: 支持各种网络应用E.g., FTP, SMTP, HTTPtransport: 进程-进程的分组传输TCP,
31、 UDPnetwork: 源主机-目的主机的分组传输IP, routing protocolslink: 相邻网络设备之间的分组传输E.g., PPP, Ethernetphysical: 在物理媒体上传输比特,Introduction,1-78,ISO/OSI reference model,presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventionssession: synchronization, chec
32、kpointing, recovery of data exchangeInternet stack “missing” these layers!these services, if needed, must be implemented in applicationneeded?,Introduction,1-79,source,applicationtransportnetworklinkphysical,segment,datagram,destination,applicationtransportnetworklinkphysical,router,switch,封装,messag
33、e,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 switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks u
34、nder attack: security1.7 History,Introduction,1-81,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 packet-switched networks1.5 Protocol layers, ser
35、vice 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 military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node op
36、erational,1972: ARPAnet public demonstrationNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet 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: Ethernet at Xerox PARCate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodes,
