Introduction1-1Chapter 1: IntroductionOur goal: get “feel” and terminology more depth, detail laterin course approach: use Internet as exampleOverview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models network modelingIntroduction1-2Chapter 1: roadmap1.1 What isthe Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 HistoryIntroduction1-3What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts = end systems running network appscommunication links fiber, copper, radio, satellite transmission rate = bandwidthrouters:forward packets (chunks of data)local ISPcompanynetworkregional ISProuterworkstationservermobileIntroduction1-4What’s the Internet: “nuts and bolts” viewprotocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPPInternet: “network of networks” loosely hierarchical public Internet versus private intranetInternet standards RFC: Request for comments IETF: Internet Engineering Task Forcelocal ISPcompanynetworkregional ISProuterworkstationservermobileIntroduction1-5What’s the Internet: a service view communication infrastructure enables distributed applications: Web, email, games, e-commerce, file sharingcommunication services provided to apps: Connectionless unreliable connection-oriented reliableIntroduction1-6What’s a protocol?human protocols: “what’s the time?” “I have a question” introductions… specific msgs sent… specific actions taken when msgs received, or other eventsnetwork protocols: machines rather than humans all communication activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receiptIntroduction1-7What’s a protocol?a human protocol and a computer network protocol:Q:Other human protocols? HiHiGot thetime?2:00TCP connectionreqTCP connectionresponseGet http://www.awl.com/kurose-ross<file>timeIntroduction1-8Chapter 1: roadmap1.1 What isthe Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 HistoryIntroduction1-9A closer look at network structure: network edge:applications and hosts network core: routers network of networksaccess networks, physical media:communication linksIntroduction1-10The network edge: end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaAIntroduction1-11Network edge: connection-oriented serviceGoal:data transfer between end systemshandshaking:setup (prepare for) data transfer ahead of time Hello, hello back human protocolset up “state”in two communicating hostsTCP - Transmission Control Protocol  Internet’s connection-oriented serviceTCP service [RFC 793]reliable, in-orderbyte-stream data transfer loss: acknowledgements and retransmissionsflow control: sender won’t overwhelm receivercongestion control: senders “slow down sending rate” when network congestedIntroduction1-12Network edge: connectionless serviceGoal:data transfer between end systems same as before!UDP - User Datagram Protocol [RFC 768]:  connectionless  unreliable data transfer no flow control no congestion controlApp’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email)App’s using UDP: streaming media, teleconferencing, DNS, Internet telephonyIntroduction1-13Chapter 1: roadmap1.1 What isthe Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 HistoryIntroduction1-14The Network Core mesh of interconnected routersthefundamental question: how is data transferred through net? circuit switching:dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks”Introduction1-15Network Core: Circuit SwitchingEnd-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup requiredIntroduction1-16Network Core: Circuit Switchingnetwork resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idleif not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time divisionIntroduction1-17Circuit Switching: FDM and TDMFDMfrequencytimeTDMfrequencytime4 usersExample:Introduction1-18Numerical example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots 500 msec to establish end-to-end circuitIntroduction1-19Network Core: Packet Switchingeach end-end data stream divided into packets user A, B packets sharenetwork resources each packet uses full link bandwidth  resources used as neededresource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time Node receives complete packet before forwardingBandwidth division into “pieces”Dedicated allocationResource reservationIntroduction1-20Packet Switching: Statistical MultiplexingSequence of A & B packets does not have fixed pattern Îstatistical multiplexing.In TDM each host gets same slot in revolving TDM frame.ABC10 Mb/sEthernet1.5 Mb/sDEstatistical multiplexingqueue of packetswaiting for outputlinkIntroduction1-21Packet switching versus circuit switching 1 Mb/s link each user:  100 kb/s when “active” active 10% of timecircuit-switching:  10 userspacket switching:  with 35 users, probability > 10 active less than