Review of Networking BasicsYao WangPolytechnic University, Brooklyn, [email protected] [Kurose/Ross]Networking Basics2Slides based on Computer Networking: A Top Down Approach Featuring the Internet, 2ndedition. Jim Kurose, Keith RossAddison-Wesley, July 2002. Chapters 1-2These slides are extracted from the slides made by authors of the book (J. F. Kurose and K. Ross), available from the publisher site for instructors. We would like to thank the authors for the excellent book and the slides.From [Kurose/Ross]Networking Basics3Overview of Telecommunication Networks and InternetBased on Chapter I -- Computer Networks and the InternetFrom [Kurose/Ross]Networking Basics4Roadmap What isthe Internet? Network edge Network core Internet structure and ISPs Protocol layers, service modelsFrom [Kurose/Ross]Networking Basics5What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts, end-systems❍ PCs workstations, servers❍ PDAs phones, toastersrunning network appscommunication links❍ fiber, copper, radio, satellite❍ transmission rate = bandwidthrouters:forward packets (chunks of data)local ISPcompanynetworkregional ISProuterworkstationservermobileFrom [Kurose/Ross]Networking Basics6What’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 ISProuterworkstationservermobileFrom [Kurose/Ross]Networking Basics7A closer look at network structure: network edge:applications and hosts network core:❍ routers❍ network of networks access networks, physical media:communication linksFrom [Kurose/Ross]Networking Basics8Network 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 congestedFrom [Kurose/Ross]Networking Basics9Network edge: connectionless serviceGoal:data transfer between end systems❍ same as before!UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service❍ 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 telephonyFrom [Kurose/Ross]Networking Basics10The 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”From [Kurose/Ross]Networking Basics11Network Core: Circuit SwitchingEnd-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup requiredFrom [Kurose/Ross]Networking Basics12Network 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 divisionFrom [Kurose/Ross]Networking Basics13Circuit Switching: TDMA and TDMAFDMAfrequencytimeTDMAfrequencytime4 usersExample:From [Kurose/Ross]Networking Basics14Network 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❍ transmit over link❍ wait turn at next linkBandwidth division into “pieces”Dedicated allocationResource reservationFrom [Kurose/Ross]Networking Basics15Packet Switching: Statistical MultiplexingSequence of A & B packets does not have fixed pattern ·statistical multiplexing.In TDM each host gets same slot in revolving TDM frame.ABC10 MbsEthernet1.5 MbsDEstatistical multiplexingqueue of packetswaiting for outputlinkFrom [Kurose/Ross]Networking Basics16Packet switching versus circuit switching 1 Mbit 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 .0004Packet switching allows more users to use network!N users1 Mbps linkFrom [Kurose/Ross]Networking Basics17Packet switching versus circuit switching Great for bursty data❍ resource sharing❍ simpler, no call setup Excessive congestion: packet delay and loss❍ protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior?❍ bandwidth guarantees needed for audio/video apps❍ still an unsolved problem (chapter 6)Is packet switching a “slam dunk winner?”From [Kurose/Ross]Networking Basics18Packet-switched networks: forwardingGoal:move packets through routers from source to destination❍ we’ll study several path selection (i.e. routing)algorithms (chapter 4)datagram network:❍destination addressin packet determines next hop❍ routes may change during session❍ analogy: driving, asking directions virtual circuit network:❍ each packet carries tag (virtual circuit ID), tag determines next hop❍ fixed path determined at call setup time, remains fixed thru call❍routers maintain per-call stateFrom [Kurose/Ross]Networking Basics19Network TaxonomyTelecommunicationnetworksCircuit-switchednetworksFDMTDMPacket-switchednetworksNetworkswith VCsDatagramNetworks• Datagram network is noteither connection-oriented or connectionless.• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.InternetFrom [Kurose/Ross]Networking Basics20Internet structure: network of networks roughly hierarchical at center: