《计算机网络与通讯》课程教学资源（PPT课件讲稿，英文版）Part I Introduction

Assignment: read Part I: Introduction chapter 1 in text O ur goa Overview: r get context r what's the Internet overview, feel " of r what's a protocol? networKing r network edge r more depth detail r network core later in course r access net, physical media r approach: m descriptive performance: loss, delay m use Internet as r protocol layers, service models backbones NAPs, ISPs example r history 1: Introduction 1

1: Introduction 1 Part I: Introduction Our goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive m use Internet as example Overview: r what’s the Internet r what’s a protocol? r network edge r network core r access net, physical media r performance: loss, delay r protocol layers, service models r backbones, NAPs, ISPs r history Assignment: read chapter 1 in text

What's the Internet: "nuts and bolts"view router r millions of connected workstation computing devices: hosts server mobile end-systems 投 al Is n pc s worksTations, servers m PDA's phones, toasters running network apps r communication links m fiber, copper, radio satellite r routers: forward packets (chunks )of data thru company network network 1: Introduction 2

1: Introduction 2 What’s the Internet: “nuts and bolts” view r millions of connected computing devices: hosts, end-systems m pc’s workstations, servers m PDA’s phones, toasters running network apps r communication links m fiber, copper, radio, satellite r routers: forward packets (chunks) of data thru network local ISP company network regional ISP router workstation server mobile

Cool"internet appliances IP picture frame http://www.ceiva.com leb-enabled toaster+weather foreca http://dancing-man.com/robin/toastyster World's smallest web server http://www-ccs.cs.umass.edu/-shri/ipic.html 1: Introduction 3

1: Introduction 3 “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster+weather forecaster http://dancing-man.com/robin/toasty/

What's the Internet: "nuts and bolts"view r protocols: control sending router workstation receiving of msgs server e.g., Tcp, Ip, Http, Ftp, PpP mobile Internet: " network of 投 al Is networks loosely hierarchical m public Internet versus regional/ISP private intranet r Internet standards RFC: Request for comments IETF: Internet Engineering Task Force company B g 1: Introduction 4

1: Introduction 4 What’s the Internet: “nuts and bolts” view r protocols: control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP r Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet r Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

What's the Internet: a service view r communication infrastructure enables distributed applications m WWW, email, games,e commerce, database ●●●口 voting, file(mP3)sharing r communication services provided connectionless connection-oriented yberspace [Gibson a consensual hallucination experienced daily by billions of operators in every nation 1: Introduction 5

1: Introduction 5 What’s the Internet: a service view r communication infrastructure enables distributed applications: m WWW, email, games, e￾commerce, database., voting, file (MP3) sharing r communication services provided: m connectionless m connection-oriented r cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in every nation,

What's a protocol? human protocols: network protocols: r" what's the time? r machines rather than ri have a question humans r introductions r all communication activity in Internet specific msgs sent governed by protocols specific actions taken protocols define format, when msas received order of msgs sent and or other events received among network entities and actions taken on msg transmission, receipt 1: Introductio 6

1: Introduction 6 What’s a protocol? human protocols: r “what’s the time?” r “I have a question” r introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: r machines rather than humans r all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

What's a protocol? a human protocol and a computer network protocol TCP connection req. TCP connection Got the re ply time? Gethttp://gaia.csumass.edu/index.htm 2:00 file time Q: Other human protocol? 1: Introduction 7

1: Introduction 7 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocol? Hi Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

A closer look at network structure r network edge: applications and hosts r network core: m routers m network of networks r access networks, physical media communication links 1: Introduction 8

1: Introduction 8 A closer look at network structure: r network edge: applications and hosts r network core: m routers m network of networks r access networks, physical media: communication links

he network edge: r end systems(hosts) m run application programs m e.g., www, email at edge of network r client/server model m client host requests, receives service from server m e.g., WWw client browser)/ server, email client/server r peer-peer model m host interaction symmetric m e.g. Gnutella, KaZaA 1: Introduction 9

1: Introduction 9 The network edge: r end systems (hosts): m run application programs m e.g., WWW, email m at “edge of network” r client/server model m client host requests, receives service from server m e.g., WWW client (browser)/ server; email client/server r peer-peer model: m host interaction symmetric m e.g.: Gnutella, KaZaA

Network edge: connection-oriented service Goal: data transfer TCP service_[RFC 793 between end sys r reliable, in-order byte- handshaking: setu stream data transfer (prepare for) data m loss: acknowledgements transfer ahead of time and retransmissions Hello. hello back human flow control proTocol m sender won 't overwhelm set up state"in two receiver communicating hosts r congestion contro/: r TCP- Transmission m senders slow down sending Control protocol rate "when network m Internet's connection congested oriented service 1: Introduction 10

1: Introduction 10 Network edge: connection-oriented service Goal: data transfer between end sys. r handshaking: setup (prepare for) data transfer ahead of time m Hello, hello back human protocol m set up “state” in two communicating hosts r TCP - Transmission Control Protocol m Internet’s connection￾oriented service TCP service [RFC 793] r reliable, in-order byte￾stream data transfer m loss: acknowledgements and retransmissions r flow control: m sender won’t overwhelm receiver r congestion control: m senders “slow down sending rate” when network congested