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 <file> 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 connectionoriented service TCP service [RFC 793] r reliable, in-order bytestream 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