1、计算机网络技术的 历史和新进展,高速计算机信息网络是信息社会的神经和血管体系结构：网络的骨架和神经协议：网络的心脏和血液,主要内容,网络概述 Internet的发展和成功经验 计算机网络技术的历史回顾 国际高速计算机网络研究计划 中国高速计算机网络研究计划,What is a Network? from end system point of view,Network offers a service: move information bird, fire, messenger, truck, telegraph, telephone, Internet another example, t
2、ransportation service: move objects horse, train, truck, airplane . What distinguish different types of networks? The services they provide What distinguish the services? latency bandwidth loss rate number of end systems service interface (how to invoke?) other details reliability, unicast vs. multi
3、cast, real-time, message vs. byte .,What is a Network? Infrastructure Centric View,Electrons and photons as communication medium Links: fiber, copper, satellite, Switches: mechanical/electronic/optical, crossbar/Banyan Protocols: TCP/IP, ATM, MPLS, SONET, Ethernet, PPP, X.25, FrameRelay, AppleTalk,
4、IPX, SNA Functionalities: routing, error control, congestion control, Quality of Service (QoS) Applications: FTP, WEB, X windows, .,Types of Networks,Geographical distance Local Area Networks (LAN): Ethernet, Token ring, FDDI Metropolitan Area Networks (MAN): DQDB, SMDS Wide Area Networks (WAN): X.2
5、5, ATM, frame relay Information type data networks vs. telecommunication networks Application type special purpose networks: airline reservation network, banking network, credit card network, telephony general purpose network: Internet,Types of Networks,Right to use private: enterprise networks publ
6、ic: telephony network, Internet Ownership of protocols proprietary: SNA open: IP Technologies terrestrial vs. satellite wired vs. wireless Protocols IP, AppleTalk, SNA,计算机网络发展历史回顾,七十年代的计算机网络 X.25 分组交换网：各国的电信部门建设运行 各种专用的网络体系结构：SNA，DNA Internet 的前身ARPANET进行实验运行 八十年代的计算机网络 标准化计算机网络体系结构：OSI 局域网络 LAN 技术空
7、前发展 建成NSFNET，Internet 初具规模 九十年代的计算机网络 Internet空前发展 Web技术在Internet/Intranet 得到广泛应用,主要内容,网络概述 Internet的发展和成功经验 计算机网络技术的历史回顾 国际高速计算机网络研究计划 中国高速计算机网络研究计划,The Internet,Global scale, general purpose, heterogeneous-technologies, public, computer network Internet Protocol open standard: Internet Engineering
8、 Task Force (IETF) as standard body technical basis for other types of networks Intranet: enterprise IP network Developed by the research community,History of the Internet,70s: started as a research project, 56 kbps, 100 computers 80-83: ARPANET and MILNET split, 85-86: NSF builds NSFNET as backbone
9、, links 6 Supercomputer centers, 1.5 Mbps, 10,000 computers 87-90: link regional networks, NSI (NASA), ESNet(DOE), DARTnet, TWBNet (DARPA), 100,000 computers 90-92: NSFNET moves to 45 Mbps, 16 mid-level networks 94: NSF backbone dismantled, multiple private backbones Today: backbones run at 2.5 / 10
10、 Gbps, 10s millions computers in 150 countries,Growth of the Internet,Number of Hosts on the Internet: Aug. 1981 213 Oct. 1984 1,024 Dec. 1987 28,174 Oct. 1990 313,000 Oct. 1993 2,056,000 Apr. 1995 5,706,000 Jul. 1997 19,540,000 Jul. 2000 93,047,785,Recent Growth (1991-2000),Internet 发展规模和趋势,Interne
11、t的发展速度 是历史上发展最快的一种技术 以商业化后达到 5000 万用户为例 电视用了13年，收音机用了38年，电话更长 Internet 从商业化后达到 5000 万用户用了4 年时间 Internet 正在以超过摩尔定理的速度发展,网络时代的三大基本定律,摩尔定律: CPU性能18个月翻番,10年100倍。 所有电子系统（包括电子通信系统，计算机）都适用,光纤定律： 超摩尔定律，骨干网带宽9个月翻番，10年10000倍。带宽需求呈超高速增长的趋势,迈特卡尔夫定律:联网定律， 网络价值随用户数平方成正比。未联网设备增加N倍，效率增加N倍。联网设备增加N倍，效率增加N2倍,网络带宽与CPU性
12、能,光纤容量,高水平大容量光纤传输试验系统,Data (Still) Overtaking Voice,0,Relative Capacity (%),Voice,Data,Source: MCI (Vint Cerf),International data traffic already exceeds international voice from Australia and Scandinavia.,2000,1998,1996,IP (Still) Conquering Data,All Other,IPX,TCP/IP,Traffic Ratios,Source: Gartner
13、1997,100%,90%,80%,70%,60%,50%,40%,30%,20%,10%,0%,Relative User Population,8%,17%,39%,27%,7%,2%,13%,18%,23%,23%,16%,7%,14%,17%,12%,15%,28%,14%,Internet (Still) Going Interactive,To Transactional Pages (Red) and Audio/Video Content (Purple),100%,80%,60%,40%,20%,0%,2000,1998,1996,Source: The Yankee Gro
14、up, 1996,Apps (Always) Driving Capacity,Simple Video, Multimedia,Browsing, PCM Voice,IP, PCS, E-Mail, File Transfer,Paging,Video Conferencing, MPEG1 NTSC Video,Telnet, VoIP,ISDN, Frame Relay,ATM/POS,T3/E3,T1/E1,New Modem,Wireless WAN,Old Modem,.004,.0192,.0288,.128,1.5,3,155,Mb/s,Minimum Bandwidth f
15、or Application per User,Virtual Reality, Medical Imaging,Data/Voice/Video Transport Convergence,高速信息网络的发展方向： 通信与计算聚合,通信和计算技术的聚合 改变了各自的原有特征 高速信息网络体系结构的发展趋势 分层结构；分布控制、管理和安全机制 分层结构 比特路层 服务层 应用层,高速信息网络的体系结构,比特路层 主干网传输技术：SDH/SONET，光纤 主干网交换技术：IP over SDH或光纤，GbE，支持IPv6 端系统接入技术：LAN；ADSL、FTTH、HFC 服务层（支撑技术） 全
16、球统一的地址、域名；安全的系统管理和访问控制 Browser/Server 计算模式，支持 Data, Voice, Video 以 Java 为代表的网络编程语言 应用层（用户功能） 用户用户（立即响应，可适当延迟） 用户服务器（立即响应，可适当延迟）,ATM,SDH/SONET,IP,Optical,IP Transport Alternatives,B-ISDN,IP over ATM,IP over SDH/SONET,IP over Optical,Long-Term Winners,IP,ATM,Optical,IP,SDH/SONET,Optical,IP,Optical,Mul
17、tiplexing, Protection, and Management at Every Layer.,Eliminating Layers Lowers Costs.,Who is Who on the Internet ?,Internet Engineering Task Force (IETF): The IETF is the protocol engineering and development arm of the Internet. Subdivided into many working groups, which specify Request For Comment
18、s or RFCs. IRTF (Internet Research Task Force): The Internet Research Task Force is a composed of a number of focused, long-term and small Research Groups. Internet Architecture Board (IAB): The IAB is responsible for defining the overall architecture of the Internet, providing guidance and broad di
19、rection to the IETF. The Internet Engineering Steering Group (IESG): The IESG is responsible for technical management of IETF activities and the Internet standards process. Standards. Composed of the Area Directors of the IETF working groups.,Internet Standardization Process,All standards of the Int
20、ernet are published as RFC (Request for Comments). But not all RFCs are Internet Standards ! available: http:/www.ietf.org A typical (but not only) way of standardization is: Internet Drafts RFC Proposed Standard Draft Standard (requires 2 working implementation) Internet Standard (declared by IAB)D
21、avid Clark, MIT, 1992: “We reject: kings, presidents, and voting. We believe in: rough consensus and running code.”,Services Provided by the Internet,Shared access to computing resources telnet (1970s) Shared access to data/files FTP, NFS, AFS (1980s) Communication medium over which people interact
22、email (1980s), on-line chat rooms, instant messaging (1990s) audio, video (1990s) replacing telephone network? A medium for information dissemination USENET (1980s) WWW (1990s) replacing newspaper, magazine? audio, video (1990s) replacing radio, CD, TV?,Todays Vision,Everything is digital: voice, vi
23、deo, music, pictures Everything is on-line: bank statement, medical record, books, airline schedule, weather, highway traffic, toaster, refrigerator Everyone is connected: doctor, teacher, broker, mother, son, friends, enemies,What is Next?,Electronic commerce virtual enterprise Internet entertainme
24、nt interactive sitcom World as a small village community organized according to interests enhanced understanding among diverse groups Electronic democracy little people can voice their opinions to the whole world bridge the gap between information haves and have nos Electronic terrorism hacker can b
25、ring the whole world to its knee,Industrial Players,Telephone companies own long-haul and access communication links, customers Cable companies own access links Wireless/Satellite companies alternative communication links Utility companies: power, water, railway own right of way to lay down more wir
26、es Medium companies own content Internet Service Providers Equipment companies switches/routers, chips, optics, computers Software companies,Backbone,ISP,ISP,Internet Physical Infrastructure,Residential Access Modem DSL Cable modem Satellite LAN,Enterprise/ISP access, Backbone transmission T1/T3, DS
27、-1 DS-3 OC-3, OC-12 ATM vs. SONET, vs. WDM,Campus network Ethernet, ATM Internet Service Providers access, regional, backbone Point of Presence (POP) Network Access Point (NAP),Links for Long Haul Transmission,Types of links T1/DS1: 1.544 Mbps T3/DS3: 44.736 Mbps STS-1/OC-1: 51.850 Mbps STS-3/OC-3:
28、155.2 Mbps STS-12/OC-12: 622.080 Mbps STS-48/OC-48: 2.488 Gbps STS-192/OC-192: 9.953 Gbps Higher levels of services offered commercially Frame Relay ATM,Possibilities IP over SDH/SONET IP over ATM IP over Frame Relay IP over WDM,Internet 的成功经验,有远见的政府不断支持：1969 有风险的企业参与和投入： NFS：MCI、IBM vBNS：MCI；Abilen
29、e: Qwest，CISCO 联合协作的开放式研究：IETF/RFC 教育和科研的示范网络为起点 具有实验物理学的研究特点 ARPAnet、NSF、ANS、vBNS 简单实用的技术路线：TCP/IP,Research and,Development,Commercialization,Partnerships,Privatization,NSFNET,Internet2, Abilene, vBNS,Advanced US Govt Networks,ARPAnet,gigabit,testbeds,Active,Nets,wireless,WDM,SprintLink,InternetMCI
30、,US Govt,Networks,ANS,Interoperable,High Performance,Research &Education,Networks,21st Century,Networking,Quality of Service,(QoS),主要内容,网络概述 Internet的发展和成功经验 计算机网络技术的历史回顾 国际高速计算机网络研究计划 中国高速计算机网络研究计划,Outline,The first design for a packet-switched network by Paul Baran in early 60s TCP/IP protocol: on
31、e realization of the basic principles in Barans design How the Internet looks like today Where it may be moving to,Paul Barans classical work “On Distributed Communications”,Time: 1960 - 1964 Goal: building a robust communication system that could survive nuclear attacks Outcome: a packet-switched n
32、etwork,What is in Barans Design,A self-adaptive system: hot-potato routing If dont know better: forwarding packets to all neighbors Update routing table by observing packets passing by; old routing entries timeout and deleted Forward packets ASAP not necessarily along shortest paths all the time Lea
33、rning & adapting to the changing environment,What is in Barans Design (cont),Datagram delivery Each switch makes packet forwarding decision based on its own routing table Each packet is forwarded independently from any others Switches keep no state about end nodes Not a most efficient network Delive
34、ry will not be perfect End systems must tolerate & recover from transmission errors,What is in Barans Design (cont),A distributed system all switch nodes are equal eliminating any single point of failure components may fail, the system must not system robustness through adequate physical redundancy
35、adaptive routing,Simulation experiment demonstrated that “extremely survivable networks can be built using a moderately low redundancy of connectivity level”Paul Baran, 1964,some less known side of the story.,at the time a number of people in telecommunication industry considered Barans proposal “to
36、tally preposterous” “they kicked, screamed, grumbled, and worse. Their response tended to be emotional, often with anger, rarely with humor”,“outsiders could not possibly understand the complexity of large systems like the telephone network”,Different approaches to system reliability,phone system at
37、 the time (still true today) Dumb end nodes, smart network making each and every network component reliable system reliability = component reliability high component reliability by local redundancy everything expected to work; failures expected to be extreme exceptions a human configured, tightly co
38、ntrolled system Baran proposal a reliable system built out of simple, unreliable parts an adaptive system that adjusts itself to changes automatically Smart ends to fix transmission errors,One Realization of Barans Desing: the Internet,interconnecting heterogeneous subnets two basic functionalities:
39、 globally unique addresses datagram delivery from sources to destinations via dynamic routing Claim: simple, flexible, scalable, and robust,IPs view of the world,IP,All kinds of subnet technologies,all kinds of applications,all kinds of transport protocols,Datagrams as the basic building block: Syst
40、em Simplicity,Each packet carries its own address One routing table serves all traffic An enabler to the explosive growth the simpler, the fewer chances to go wrong the simpler, the easier to grow the requirement of least common network functionality maximizes the number of usable networks,Datagrams
41、 as the basic building block: Flexibility,“runs over anything” IP started with ARPANET, PRNET, SATNET; all long gone today IP runs over 100 Mb or Gb/s Ethernet, FDDI, Frame Relay, ATM, SONET, DWDM Supports all different applications used to be telnet, ftp, email only now audio, video, web, e-commerc
42、e, online-education,What will the future bring?The best bet would be to stay flexible,Datagrams as the basic building block: Scalability,To scale the system must be able to gracefully handle the growth in the total number of end systems the growth in traffic volume the growth in network size larger
43、routing tables More frequent changes,With IP, “the network knows nothing about individual end applications; end applications know nothing about network internals”Van Jacobsonmade it possible to aggregate routing table entries according to scaling need,Datagrams as the basic building block: Robustnes
44、s,self-adaptive nature of dynamic routing facilitated the growth dynamic routing and datagram delivery go hand-in-hand periodic routing updates: “are you still there” silent assumption: existing parts may fail, new parts may appear any time changes considered the norm rather than exceptions trades o
45、ff optimal link usage (e.g. header overhead, update overhead) for system robustness,“Unintended consequence” ?,In a casual conversation Noel Chiappa said, without DoDs Internet research initiative “Perhaps wed have discovered computer networks eventually, but I have no idea when; . Its also unclear
46、if wed have the kind of network we do if it hadnt been intended for such a use.,“A spirit of intense robustness, and the ability to keep going no matter what, has been part of the Internet ethic since day one, and it is due in part to the rather severe operation environment for which it was original
47、ly intended. This extremely monolithic nature of the Internet is one of the things which is making it hostile to control, and perhaps that is in some part due to the original goals of the network.”,“Why a tougher system?”,things do go wrong from time to time, despite all the honest efforts to preven
48、t them Have a guess on how often network outage happens? Get worse as the system grows larger “What sort of changes would be helpful in next generation networks? Of course higher data rate and lower cost are desirable, but of all parameters I would opt for greater emphasis on robustness.” Paul Baran
49、, 1977,How the Internet looks like today,No longer the same as 20 years ago A lot bigger A lot more users A lot more useful, a lot more valuable less robust, less adaptive, and less connected . Effectively we were out of IPv4 address space some years ago most users are connected via Network Address Translator (NAT) now,
