Computer Networking A Top-Down Approach Featuring the Internet 计算机网络 - 自顶向下方法与 Internet 特色 - PowerPoint PPT Presentation

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  1. Computer NetworkingA Top-Down Approach Featuring the Internet计算机网络-自顶向下方法与Internet特色 Chapter1 Computer Networks and the Internet

  2. Introduction • Chapter goal • get context, overview, and “feel” of computer networking • more depth, detail later in the course • approach: • descriptive • use Internet as example

  3. roadmap • What is the Internet? • The Network edge • The Network core • Access networks and physical media • ISPs and Internet backbones • Delay & loss in packet-switched networks • Protocol layersand their service models • Historyof networking and the Internet

  4. 1.1 What’s the Internet? • Nuts-and-bolts description • the basic hardware and software components that make up the Internet. • Computing devices, communication links, switches,…… • A service description • describing the Internet in terms of a networking infrastructure that provides services to distributed applications. • Connection-oriented reliable service • Connectionless unreliable service

  5. router workstation server mobile local ISP regional ISP company network 1 A Nuts-and-Bolts view • End systems • public Internet is a worldwide computer network that connects millions of computing devices • pc’s workstations, servers, PDA’s phones, even toasters. • hosts • The term computer network is being to sound a bit dated! 1.1What’s the Internet?

  6. Host Count in the Internet

  7. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • communicationlinksconnect the end systems together to form a network • fiber, copper, radio, satellite,…… • transmission rate: bits per second (bps) 1.1 What’s the Internet?

  8. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • End systems are usually connected to each other through packet switches. • forward arrivalpacketsfrom input to output • a packet is a chunk of data. • Router andLink-layer switch • forward packets thru network according to the value of header field 1.1What’s the Internet?

  9. Example-A Packet

  10. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • route/ path • links and switches sequence that a packet traversed from a source to the destination end system • In the Internet, the routeis dynamic , and not dedicated. • packet switching • allows multiple communicating end systems to share a link, a switch, or the whole path. 1.1What’s the Internet?

  11. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view 1.1What’s the Internet? local ISP B regional ISP A company network

  12. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • End system access the Internet through the ISP. • Internet Service Provider • Each ISP is a network of packet switches and communication links. 1.1What’s the Internet?

  13. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • protocols control the sending and receiving of information within the Internet. • Protocols are rules must be obeyed. • TCP/IP • TCP: transmission control protocol • IP: Internet protocol • Internet standards • RFC: Request for comments/请求注释 • IETF: Internet Engineering Task Force • IEEE: Institute of Electrical and Electronics Engineers 1.1What’s the Internet?

  14. 1 A Nuts-and-Bolts view 1 A Nuts-and-Bolts view • public Internet vs. private intranet • Internet is a network of networks • public Internet:the network that one typically refers to astheInternet, that is, the global network of networks • extranet • private Internet: heir hosts cannot exchange messages with hosts outside of the private network • intranet 1.1What’s the Internet?

  15. Brief summary • End systems/hosts • Communication links • Packet switches • Route or Path • ISP • Protocols • Public Internet and private Intranet 1.1What’s the Internet?

  16. 2 A Service Description 2 A Service Description • The Internet enables distributed applications • WWW, email, e-commerce, database, voting, … • Everything over IP! • connection-oriented reliable service • guarantees that data transmitted from a sender to a receiver will eventually be delivered to the receiver in order and in its entirety • Connectionless unreliable service • without any guarantees about the eventually delivery 1.1What’s the Internet?

  17. 3 What’s a protocol? 3 What’s a protocol? human protocols: • “what’s the time?” • “I have a question” • Introductions …there are specific msgs we send, and specific actions we take in response to the received reply msgs or other events 1.1What’s the Internet?

  18. 3 What’s a protocol? 3 What’s a protocol? network protocols: • machines, rather than humans, exchange msgs • all communication activity in Internet governed by protocols protocols define format,orderof msgs exchanged between network entities, and actionstaken on msg transmission, receiptor other events 1.1What’s the Internet?

  19. Hi TCP connection req. TCP connection reply. Hi Get http://www2.sdai.edu.cn/index.htm Got the time? 2:00 <file> time 3 What’s a protocol? 3 What’s a protocol? human protocol and computer network protocol: 1.1What’s the Internet? what’s the time?

  20. 1.1 What’s the Internet?-summary • Nuts-and-bolts description • the basic hardware and software components that make up the Internet. • A service description • describing the Internet in terms of a networking infrastructure that provides services to distributed applications. • Protocols • define format, orderof msgs exchanged between network entities, and actions taken on msg transmission, receiptor other events.

  21. roadmap • What is the Internet? • The Network edge • The Network core • Access networks and physical media • ISPs and Internet backbones • Delay & loss in packet-switched networks • Protocol layersand their service models • Historyof networking and the Internet

  22. network edge: hosts and applications services network core: routers and switches Circuit/Packet switching access networks, physical media: physical media access types Introduction Introduction 1.2 The Network Edge

  23. Computers connected to the Internet are referred to as end systems. sit at the edge of the Internet run application programs, so also referred to as host. e.g., WWW, email,…… 1 End systems 1 End systems 1.2 The Network Edge

  24. 1 Clients, and Servers 1 Clients, and Servers • Two categories of hosts : Clients and Servers • Client (program) host requests, receives service from server (program) • Client/Server Internet applications are distributed applications • Client program runs on one PC, and the server program runs on another PC. 1.2 The Network Edge

  25. 1 Clients, and Servers 1 Clients, and Servers • Peer to Peer model(P2P): • host interaction symmetric • e.g.: • teleconferencing • emule 1.2 The Network Edge

  26. 2 Services 2 Services • End system programs use the services of the Internet to exchange messages. • Connectionless service • UDP: user datagram protocol • 用户数据报协议 • Connection-oriented service • TCP: transmission control protocol • 传输控制协议 1.2 The Network Edge

  27. 2 Connection-Oriented Service 2 Connection-Oriented Services • Connection-Oriented service • handshaking • setup (prepare for) data transfer ahead • sends control packets to each other to establish the connection. • end system allocates resources for the connection • buffer/bandwidth/states 1.2 The Network Edge

  28. 2 Connection-Oriented Services • Whyconnection-orientedand not justconnection? • Connection established between hosts is very loose and only the end systems are aware of the connection. • Only the end system allocates buffers , state,.., fort the connection 1.2 The Network Edge

  29. 2 Connectionless Service 2 Connectionless Service • Connectionless Service = no handshaking • UDP (User Datagram Protocol) 1.2 The Network Edge

  30. 2 Services 2 Services • TCP or UDP? • Apps using TCP • WWW, FTP, E-mail,… • Apps using UDP • Internet Phone, video-conferencing,… • If the apps want control what and when the data sent, choose UDP. • If apps want reliable data transfer, choose TCP. 1.2 The Network Edge

  31. Summary • End systems/hosts are sit at the edge of the Internet, and host applications. • Client/Server • P2P • End systems use the services of the Internet to send msgs to each other • Connection-oriented service:TCP • Connectionless service:UDP • Applications choose transport service according to their requirements. 1.2 The Network Edge

  32. roadmap • What is the Internet? • The Network edge • The Network core • Access networks and physical media • ISPs and Internet backbones • Delay & loss in packet-switched networks • Protocol layersand their service models • Historyof networking and the Internet

  33. Introduction Introduction • Network core is a mesh of routers and links that interconnect the hosts. 1.3 The Network Core

  34. 1. Switching techniques • Two approaches to build a network core • circuit switching:dedicatedcircuit per call • telecommunication network • packet-switching: data sent thru net in discrete “chunks” (packets) • Internet 1.3 The Network Core

  35. 1. Switching techniques • Circuit Switching • Reserveresources needed along a path for any call for the duration of the session. • bandwidth and/or switch capacity • dedicatedresources allocation • guaranteed performance • call setuprequired 1.3 The Network Core

  36. 1. Switching techniques • Packet Switching • Resources are used on demand • Resources are shared with other sessions • No performance guarantee 1.3 The Network Core

  37. Circuit Switching Circuit Switching 1.3 The Network Core

  38. Multiplexing in Circuit Switched Networks • There are lots of circuits in a link. How to implement a circuit? • network resources (e.g., bandwidth) divided into“pieces” • a piece allocated to one call • resource piece idle if not used by the owning call (no sharing) 1.3 The Network Core

  39. What’s multiplexing? • Multiplexing is sending multiplesignals on a carrierat the same time in the form of a complex signal and then recovering the separate signals at the receiving end. • frequency-division multiplexing-FDM • Wavelength division multiplexing-WDM • time-division multiplexing-TDM • code-division multiplexing-CDM 1.3 The Network Core

  40. FDM • The frequency spectrum of a link is divided into bands and shared among the connections established across the link. • Bandwidth: the width of the band 1.3 The Network Core

  41. 干涉 interference

  42. TDM • For a TDM link, time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots. • The network dedicates one time slot in every frame to the connection. 1.3 The Network Core

  43. TDM and FDM

  44. Packet Switching Packet Switching • Long msgsare broken into packets. • There has a destination addressof the destination in each packet and used by the packetswitches to determine output link • Packets are transmitted over each link at fullrate of the link • resources used asneeded, no setup • Resources are shared among multiple user 1.3 The Network Core

  45. Packet Switching : Store-and-Forward transmission • Packet Switches must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link. • it introduces a store-and-forward delay at the input to each link along the path. • The delay is proportional to the packet’s length • Packet Length = L bits and the link rate =R bps • Store-and-forward delay=L/R s 1.3 The Network Core

  46. Packet Switching: Store-and-Forward transmission • Packet length: L bits; • Q links from source to destination • link rate: R bps • no queuing delay and no propagations delay • store and forward delay in each link is L/R s • end to end delay is QL/R s 1.3 The Network Core

  47. Packet Switching:Buffering in Packet Switches • If a packet needs to be transmitted across a link that is busy now, it must be stored in the buffer temporarily and wait for its turn. • Queueing delay • Packet loss: if the buffer overflows 1.3 The Network Core

  48. D E Statistical Multiplexing of Packet Switched Network • Sequence of A & B packets does not have fixed pattern  statistical multiplexing. • In TDM each host gets same slot in revolving TDM frame. 1.3 The Network Core C A statistical multiplexing B

  49. N users 1 Mbps link Packet switching vs. Circuit switching • Packet switching allows more users to use network than circuit switching! • For Example: • 1 Mbps link • each user: • 100 kbps when “active” • active 10% of time • circuit-switching: • 10 users • packet switching: • with 35 users, probability > 10 active less than .0004 1.3 The Network Core

  50. Packet switching vs. Circuit switching • Packet switches can send data at full rate of the outbound link. • Example • 10users, one suddenly generate one 1000-bit packet, while others remain silent. • Link rate is 1Mbps, each user 100kbps • Under circuit switching • 1000/100000=10msec • Under packet switching • 1000/1000000=1msec 1.3 The Network Core