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컴퓨터 네트워크 개념, 프로토콜, 프로그래밍 임 효 택, 송 주 석 E-mail: htlim@dongseo. ac. kr Home page: http: //kowon. dongseo. ac. kr/~htlim 1

컴퓨터 네트워크 구조의 예: Internet n millions of connected computing devices: hosts, end-systems l l pc’s workstations, servers PDA’s phones, toasters router server regional ISP communication links l n mobile local ISP running network apps n workstation fiber, copper, radio, satellite routers: forward packets (chunks) of data thru network company network 8

What’s the Internet: “nuts and bolts” view n protocols: control sending, receiving of msgs l n e. g. , TCP, IP, HTTP, FTP, PPP router server mobile local ISP Internet: “network of networks” l l n workstation regional ISP loosely hierarchical public Internet versus private intranet Internet standards l l RFC: Request for comments IETF: Internet Engineering Task Force company network 9

What’s the Internet: a service view n communication infrastructure enables distributed applications: l l n communication services provided: l l n WWW, email, games, ecommerce, database. , voting, more? connectionless connection-oriented cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in every nation, . . " 10

What’s a protocol? human protocols: n “what’s the time? ” n “I have a question” n introductions network protocols: n machines rather than humans n all communication activity in Internet governed by protocols … specific msgs sent … specific actions taken when msgs received, or other events protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt 11

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection req. Hi TCP connection reply. Got the time? Get http: //gaia. cs. umass. edu/index. htm 2: 00 <file> time Q: Other human protocol? 12

A closer look at network structure: n n network edge: applications and hosts network core: l l n routers network of networks access networks, physical media: communication links 13

The network edge: n end systems (hosts): l l l n client/server model l l n run application programs e. g. , WWW, email at “edge of network” client host requests, receives service from server e. g. , WWW client (browser)/ server; email client/server peer-peer model: l l host interaction symmetric e. g. : teleconferencing 14

Network edge: connection-oriented service Goal: data transfer n between end sys. handshaking: setup (prepare for) data transfer ahead of time l l n Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol l Internet’s connection -oriented service TCP service [RFC 793] n reliable, in-order bytestream data transfer l n flow control: l n loss: acknowledgements and retransmissions sender won’t overwhelm receiver congestion control: l senders “slow down sending rate” when network congested 15

Network edge: connectionless service Goal: data transfer between end systems l n same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service l unreliable data transfer l no flow control l no congestion control App’s using TCP: n HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: n streaming media, teleconferencing, Internet telephony 16

n 표준화 기구 – – – ANSI (American National Standards Institute) IEEE (Institute for Electrical and Electronics Engineers) ITU-T (International Telecommunications Union Telecommunications), CCITT ETSI (European Telecommunications Standards Institute) ISO (International Standards Organization) 23

TCP/IP n n 미국 국방성의 ARPANET 인터넷(Internet) 27

IEEE LAN, MAN n n LAN (Local Area Network) MAN (Metropolitan Area Network) 29