第1章计算机网络体系结构与Internet_873607670

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,1,计算机网络体系结构与,Internet,徐 恪,清华大学计算机系,2,提纲,网络基本概念,Internet,简介,协议分层和,OSI,参考模型,End-to-End Arguments,Internet,设计原则,基本机制回顾,3,提纲,网络基本概念,Internet,简介,协议分层和,OSI,参考模型,End-to-End Arguments,Internet,设计原则,基本机制回顾,4,“,Cool,”,Internet appliances,Worlds smallest web server,http:/www-ccs.cs.umass.edu/shri/iPic.html,IP picture frame, toaster+weather forecaster,5,What,s a network,network edge:,millions of end-system devices:,pc,s workstations, servers,PDA,s, phones, toasters,running network apps,network core:,routers, switches forwarding data,packets:,packet switching,calls:,circuit switching,communication links,fiber, copper, radio,local net,company,net,regional net,router,workstation,server,mobile,6,What,s a protocol?,a human protocol and a computer network protocol:,Hi,Hi,Got the,time?,2:00,TCP connection,req.,TCP connection,reply.,Get ,time,7,What,s a protocol?,human protocols:,“,what,s the time?,”,“,I have a question,”,Introductions,network protocols:,machines rather than humans,all communication activity in Internet governed by protocols,specific msgs sent,specific actions taken when msgs received, or other events,8,What,s a protocol?,protocols define,format,order of msgs,sent and received among network entities, and,actions,taken on msg transmission, receipt,9,A closer look at network structure,network edge:,applications and hosts,network core:,routers,network of networks,access networks, physical media:,communication links,10,The network edge,end systems (hosts),run application programs,e.g., WWW, email,at,“,edge of network,”,client/server model,client host requests, receives service from server,e.g., WWW client (browser)/ server; email client/server,peer-peer model,host interaction symmetric,e.g.: BT, Maze, e-Donkey,11,The network core,mesh of interconnected routers,the,fundamental question:,how is data transferred through net?,circuit switching:,dedicated circuit per call: telephone net,packet switching:,data sent thru net in discrete,“,chunks,”,12,Communication networks can be classified based on the way in which the nodes exchange information:,A Taxonomy of Communication Networks,Communication Network,SwitchedCommunication Network,BroadcastCommunication Network,Circuit-SwitchedCommunication Network,Packet-SwitchedCommunication Network,Datagram Network,Virtual Circuit Network,13,Broadcast communication networks,Information transmitted by any node is received by,every,other node in the network,E.g., LANs (Ethernet, Wavelan),Problem:,coordinate the access of all nodes to the shared communication medium (Multiple Access Problem),Switched communication networks,Information is transmitted to a sub-set of designated nodes,E.g., WANs (Telephony Network, Internet),Problem:,how to forward information to intended node(s),Done by special nodes (e.g., routers, switches) running routing protocols,Broadcast vs. Switched Communication Networks,14,Communication networks can be classified based on the way in which the nodes exchange information:,A Taxonomy of Communication Networks,Circuit-SwitchedCommunication Network,Communication Network,SwitchedCommunication Network,BroadcastCommunication Network,Packet-SwitchedCommunication Network,Datagram Network,Virtual Circuit Network,15,Circuit Switching,Three phases,circuit establishment,data transfer,circuit termination,If circuit not available:,“Busy signal”,Examples,Telephone networks,ISDN (Integrated Services Digital Networks),16,Timing in Circuit Switching,DATA,Circuit Establishment,Data Transmission,Circuit Termination,Host 1,Host 2,Node 1,Node 2,propagation delay,between Host 1,and Node 1,propagation delay,between Host 2,and Node 1,processing delay at Node 1,17,Circuit Switching,A node (switch) in a circuit switching network,incoming links,outgoing links,Node,18,Circuit Switching: Multiplexing/Demultiplexing,Time divided in,frames,and frames divided in,slots,Relative slot position inside a frame,determines,which conversation the data belongs to,Needs,synchronization,between sender and receiver,In case of non-permanent conversations,Needs to,dynamic,bind a slot to a conservation,19,Communication networks can be classified based on the way in which the nodes exchange information:,A Taxonomy of Communication Networks,Communication Network,SwitchedCommunication Network,BroadcastCommunication Network,Circuit-SwitchedCommunication Network,Packet-SwitchedCommunication Network,Datagram Network,Virtual Circuit Network,20,Packet Switching,Data are sent as formatted bit-sequences, so-called,packets,Packets have the following structure:,Header and Trailer carry control information (e.g., destination address, checksum),Each packet is passed through the network from node to node along some path (,Routing,),At each node the entire packet is received, stored briefly, and then forwarded to the next node (,Store-and-Forward,Networks,),Typically no capacity is allocated for packets,Header,Data,Trailer,21,Packet Switching,A node in a packet switching network,incoming links,outgoing links,Node,Memory,22,Packet Switching: Multiplexing/Demultiplexing,Data can be transmitted at any given time,How to tell them apart?,Use,meta-data (header),to describe data,23,Communication networks can be classified based on the way in which the nodes exchange information:,A Taxonomy of Communication Networks,Communication Network,SwitchedCommunication Network,BroadcastCommunication Network,Circuit-SwitchedCommunication Network,Packet-SwitchedCommunication Network,Datagram Network,Virtual Circuit Network,24,Datagram Packet Switching,Each packet is,independently,switched,Each packet header contains destination address,No resources are pre-allocated (reserved) in advance,Example: IP networks,25,Datagram Packet Switching,Host A,Host B,Host E,Host D,Host C,Node 1,Node 2,Node 3,Node 4,Node 5,Node 6,Node 7,26,How do loss and delay occur?,packets,queue,in router buffers,packet arrival rate to link exceeds output link capacity,packets queue, wait for turn,A,B,packet being transmitted,(delay),packets queueing,(delay),free (available) buffers: arriving packets,dropped (,loss,) if no free buffers,27,Four sources of packet delay,1. nodal processing,check bit errors,determine output link,A,B,propagation,transmission,nodal,processing,queueing,2. queueing,time waiting at output link for transmission,depends on congestion level of router,28,Four sources of packet delay,3. Transmission delay:,R=link bandwidth (bps),L=packet length (bits),time to send bits into link = L/R,4. Propagation delay:,d = length of physical link,s = propagation speed in medium (2x10,8,m/sec),propagation delay = d/s,A,B,propagation,transmission,nodal,processing,queueing,Note:,s and R are,very,different quantities!,29,Communication networks can be classified based on the way in which the nodes exchange information:,A Taxonomy of Communication Networks,Communication Network,SwitchedCommunication Network,BroadcastCommunication Network,Circuit-SwitchedCommunication Network,Packet-SwitchedCommunication Network,Datagram Network,Virtual Circuit Network,30,Virtual-Circuit Packet Switching,Hybrid of,circuit,switching and,packet,switching,Data is transmitted as packets,All packets from one packet stream are sent along a,pre-established path,(=virtual circuit),Guarantees in-sequence delivery of packets,However,: Packets from different virtual circuits may be interleaved,Example: ATM networks,31,Virtual-Circuit Packet Switching,Communication with virtual circuits takes place in three phases,VC establishment,data transfer,VC disconnect,Note:,packet headers don,t need to contain the full destination address of the packet,32,Packet 1,Packet 2,Packet 3,Packet 1,Packet 2,Packet 3,Timing of,Virtual-Circuit Packet Switching,Packet 1,Packet 2,Packet 3,Host 1,Host 2,Node 1,Node 2,propagation delay,between Host 1,and Node 1,VC,establishment,VC,termination,Data,transfer,33,Virtual-Circuit Packet Switching,Host A,Host B,Host E,Host D,Host C,Node 1,Node 2,Node 3,Node 4,Node 5,Node 6,Node 7,34,Packet-Switching vs. Circuit-Switching,Most important advantage of packet-switching over circuit switching: ability to exploit,statistical multiplexing,Efficient bandwidth usage,ratio between peek and average rate is 3:1 for audio, and 15:1 for data traffic,35,Packet-Switching vs. Circuit-Switching,However, packet-switching needs to deal with,congestion,More complex routers,Harder to provide good network services (e.g., delay and bandwidth guarantees),In practice they are,combined,IP over SONET, IP over Frame Relay,36,提纲,网络基本概念,Internet,简介,协议分层和,OSI,参考模型,End-to-End Arguments,Internet,设计原则,基本机制回顾,37,The Internet,Global scale, general purpose, heterogeneous-technologies, public, computer network,Internet Protocol,Open standard:,Internet Engineering Task Force (IETF) as standard body,http:/www.ietf.org,Technical basis for other types of networks,Intranet: enterprise IP network,Developed by the research community,38,Internet History,1961:,Kleinrock - queueing theory shows effectiveness of packet-switching,1964:,Baran - packet-switching in military nets,1967:,ARPAnet conceived by Advanced Research Projects Agency,Larry Roberts,1969:,first ARPAnet node operational,1972:,ARPAnet demonstrated publicly,NCP (Network Control Protocol) first host-host protocol,first e-mail program,ARPAnet has 15 nodes,1961-1972: Early packet-switching principles,39,Internet History,1970:,ALOHAnet satellite network in Hawaii,1973:,Metcalfe,s PhD thesis proposes Ethernet,1974:,Cerf and Kahn - architecture for interconnecting networks,late 70s:,proprietary architectures: DECnet, SNA, XNA,late 70s:,switching fixed length packets (ATM precursor),1979:,ARPAnet has 200 nodes,Cerf and Kahns internetworking principles:,minimalism, autonomy,no internal changes required to interconnect networks,best effort service model,stateless routers,decentralized control,define todays Internet architecture,1972-1980: Internetworking, new and proprietary nets,40,Internet History,1982:,SMTP e-mail protocol defined,1983:,deployment of TCP/IP,1983:,DNS defined for name-to-IP-address translation,1985:,FTP protocol defined,1988:,TCP congestion control,new national networks: Csnet, BITnet, NSFnet, Minitel,100,000 hosts connected to confederation of networks,1980-1990: new protocols, a proliferation of networks,41,Internet History,Early 1990s:,ARPAnet decommissioned,1991:,NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995),early 1990s:,Web,hypertext Bush 1945, Nelson 1960,s,HTML, HTTP: Berners-Lee,1994: Mosaic, later Netscape,late 1990,s: commercialization of the Web,Late 1990s 2000s:,more killer apps: instant messaging, peer2peer file sharing (e.g., BT, Napster),network security to forefront,est. 50 million host, 100 million+ users,backbone links running at Gbps,1990, 2000s: commercialization, the Web, new apps,42,Time Line of the Internet,Source: Internet Society,43,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,Jan. 1997 16,146,000,Jan. 1999 56,218,000,Jan. 2001 109,374,000,Jan. 2003 171,638,297,Jan. 2006 394,991,609,July 2007 489,774,269,Jan. 2009 625,226,456,July 2009 681,064,561,July 2010 768,913,036,Data available at: http:/www.isc.org/,44,Growth of the Internet,45,Who is Who in the Internet ?,Internet Society (ISOC),ISOC is a professional membership society with more than 100 organization and over 28,000 individual members in over 180 countries,It provides leadership in addressing issues of the Internet, and is the organization home for the groups responsible for Internet infrastructure standards, including IETF and IAB,46,Who is Who in 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 Comments or RFCs,47,Who is Who in the Internet ?,IRTF (Internet Research Task Force),The Internet Research Task Force is 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 direction to the IETF,48,Who is Who in the Internet ?,The Internet Engineering Steering Group (IESG),The IESG is responsible for technical management of IETF activities and the Internet standards process,Composed of the,Area Directors,of the IETF working groups,49,Who is Who in the Internet ?,IETF and IESG Chair,Russ Housley, Vigil Security, LLC,Applications Area (app),Alexey Melnikov, Isode Limited,Peter Saint-Andre, Cisco,Internet Area (int),Jari Arkko, Ericsson,Ralph Droms, Cisco,Operations and Management Area (ops),Ronald Bonica, Juniper Networks,Dan Romascanu, Avaya,Real-time Applications and Infrastructure Area (rai),Gonzalo Camarillo,Ericsson,Robert Sparks, Tekelec,Routing Area (rtg),Stewart Bryant, Cisco,Adrian Farrel,Huawei,Security Area (sec),Tim Polk, National Institute of Standards and Technology,Sean Turner, IECA, Inc.,Transport Area (tsv),Lars Eggert, Nokia Research Center,David Harrington, HuaweiSymantec,50,Internet Standardization Process,All standards of the Internet 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:,BOF (Birds of a feather),Internet Drafts,RFC,Proposed Standard,Draft Standard (requires 2 working implementation),Internet Standard (declared by IAB),51,Internet Standardization Process,David Clark, MIT, 1992:,We reject: kings, presidents, and voting. We believe in: rough consensus and running code.,52,Services Provided by the Internet,Shared access to computing resources,Telnet (1970,s),Shared access to data/files,FTP, NFS, AFS (1980,s),Communication medium over which people interact,Email (1980,s), on-line chat rooms (1990,s),Instant messaging, IP Telephony (2000,s),53,Services Provided by the Internet,A medium for information dissemination,USENET (1980,s),WWW (1990,s),Replacing newspaper, magazine?,Audio, video (2000,s),Replacing radio, CD, TV,54,Internet structure: network of networks,roughly hierarchical,at center: “tier-1” ISPs,(e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage,treat each other as equals,Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,Tier-1 providers interconnect (peer) privately,NAP,Tier-1 providers also interconnect at public network access points (NAPs),Tier-1 ISP: e.g., AT&T,56,Tier-1 ISPs,http:/en.wikipedia.org/wiki/Tier_1_network,57,Internet structure: network of networks,“Tier-2” ISPs: smaller (often regional) ISPs,Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs,Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,NAP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet,tier-2 ISP is c,ustomer,of,tier-1 provider,Tier-2 ISPs also peer privately with each other, interconnect at NAP,58,Internet structure: network of networks,“Tier-3” ISPs and local ISPs,last hop (,“,access,”,) network (closest to end systems),Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,NAP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,local,ISP,local,ISP,local,ISP,local,ISP,local,ISP,Tier 3,ISP,local,ISP,local,ISP,local,ISP,Local and tier- 3 ISPs are,customers,of,higher tier ISPs,connecting them to rest of Internet,59,Internet structure: network of networks,a packet passes through many networks!,Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,NAP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,Tier-2 ISP,local,ISP,local,ISP,local,ISP,local,ISP,local,ISP,Tier 3,ISP,local,ISP,local,ISP,local,ISP,Try a traceroute!,60,61,62,63,64,65,Access Networks,Q: How to connect end systems to edge router?,residential access nets,institutional access networks (school, company),mobile access networks,Keep in mind:,bandwidth (bits per second) of access network?,shared or dedicated?,66,Residential access: point to point access,Dialup via modem,up to 56Kbps direct access to router (often less),ISDN:,integrated services digital network,128kbps + regular phone line,ADSL:,asymmetric digital subscriber line,up to 1 Mbps upstream (today typically 256 kbps),up to 8 Mbps downstream (today typically 1 Mbps),FDM: 50 kHz - 1 MHz for downstream,67,Residential access: point to point access,ADSL:,asymmetric digital subscriber line,充分利用了双绞铜线的频谱,传统话音业务频段，,4,带宽,上行双工低速信道，在话音频谱之上,下行单工高速信道，位于高频部分,频分多路复用,(FDM),或回波抵消,(Echo Cancellation),技术,在回波抵消,ADSL,系统中，下行信道与上行信道有重叠,(,主要是利用低频部分信号衰减小的特点,),与频分复用技术相比，回波抵消技术消除了因频率叠加所带来的干涉,(,如近端串音,),，可使,ADSL,系统在性能指标上有较大的提高，复杂度较高,68,Residential access: cable modems,HFC: hybrid fiber coax,asymmetric: up to 10Mbps upstream, 30 Mbps downstream,network,of cable and fiber attaches homes to ISP router,shared access to router among home,issues: congestion, dimensioning,deployment: available via cable companies, e.g., ComCast,69,Residential access: cable modems,Diagram: Network Architecture: Overview,home,cable headend,cable distribution,network (simplified),Typically 500 to 5,000 homes,71,Cable Network Architecture: Overview,home,cable headend,cable distribution,network,server(s),72,Cable Network Architecture: Overview,home,cable headend,cable distribution,network (simplified),73,Cable Network Architecture: Overview,home,cable headend,cable distribution,network,Channels,V,I,D,E,O,V,I,D,E,O,V,I,D,E,O,V,I,D,E,O,V,I,D,E,O,V,I,D,E,O,D,A,T,A,D,A,T,A,C,O,N,T,R,O,L,1,2,3,4,5,6,7,8,9,FDM:,74,Company access:local area networks,company/univ,local area network,(LAN) connects end system to edge router,Ethernet:,shared or dedicated link (switched Ethernet) connects end system and router,10 Mbps, 100Mbps, Gigabit Ethernet,deployment:,institutions, home LANs happening now,To/From,ISP,75,Wireless access networks,shared,wireless,access network connects end system to router,via base station aka,“,access point,”,wireless LANs:,802.11b: 11 Mbps,802.11g: 54 Mbps,802.11n: Marvell,提供,450Mbps,wider-area wireless access,provided by telecom operator,3G ,2 Mbit/s,for stationary or walking users, and,384 kbit/s,in a moving,vehicle,WCDMA/CDMA2000/TDS-CDMA in China,base,station,mobile,hosts,router,76,Home networks,Typical home network components:,ADSL or cable modem,router/firewall/NAT,Ethernet,wireless access point,wireless,access,point,wireless,laptops,router/,f