CS551ComputerCommunicationsBill Chenghttp://merlot.usc.edu/cs551-f121 Computer Communications - CSCI 551 Copyright © William C. ChengIntroductionDesign principlesUnicast routingTCP and congestionWireless systemsPeer-to-peer systemsMulticast routing2Course Topics (Tentative) Computer Communications - CSCI 551 Copyright © William C. ChengInter-domain routingIntegrated anddifferentiated servicesMeasurementsTopology modelingTentative topicsTraffic modelingWeb performance andcachingCurrent topicsSecurityWe will not deal with how bits move in physical media -you did this in your undergrad classProtocols and mechanisms3Focus of the Class Computer Communications - CSCI 551 Copyright © William C. ChengProtocol rules and algorithmsWe will deal with:Investigate mechanism tradeoffsWhy this way and not another?4The Internet, Circa 1969 Computer Communications - CSCI 551 Copyright © William C. ChengIMPUCLAXOSD-7IMPSRIXOS940IMPUTAHDECPDP-10UCSBIBM360/75IMP5A Recent Internet ISP Map Computer Communications - CSCI 551 Copyright © William C. Cheng6The Internet, on a Poster,Circa 2000 Computer Communications - CSCI 551 Copyright © William C. Cheng[data courtesy ofUCSD’s caida]Quote from a t-shirt commonly worn at IETF meetings:7Internet Development Mantra Computer Communications - CSCI 551 Copyright © William C. Cheng"We reject kings, presidents and voting.We believe in rough consensus andrunning code." [Dave Clark]8Glimpses of the Future? Computer Communications - CSCI 551 Copyright © William C. Chenga sensor network(tracking the truck)http://www.picoweb.net/(an 8-bit web server withEthernet)UCB mote:an 8-bit sensor nodewith non-IP basednetworkingWire or wireless.Host: computer, PDA, light switch, ...9Some Definitions Computer Communications - CSCI 551 Copyright © William C. ChengLink: path followed by bits.Broadcast or switched (or both).Packet switching: stateless, store&forward.Switch: moves bits between links.Circuit switching: stateful, cut through.Point-to-Point10Networks Computer Communications - CSCI 551 Copyright © William C. ChengMultiple AccessWirelessTwo or more nodesconnected by a link,orA network can be defined recursively as...11Switched Networks Computer Communications - CSCI 551 Copyright © William C. ChengTwo or more networksconnected by one or morenodes12What Is the Problem? Computer Communications - CSCI 551 Copyright © William C. ChengTechnology?Applications?Robustness?Technology?13What Is the Problem? Computer Communications - CSCI 551 Copyright © William C. ChengTechnology?Applications?Robustness?Technology?Number of hosts, globally routableAlways define what kind of scale you mean14But What to Scale? Computer Communications - CSCI 551 Copyright © William C. ChengNetwork should support many link layersGeographic distanceMany versions of software, hardware technologiesRange of bandwidthsDifferent application needs (QoS, etc)Levels of trust / administrative boundariesRange of price points for hardwareLots of dimensions of scaling to considerTechnological issuesSometimes easy to forget in this course15Applications Rule! Computer Communications - CSCI 551 Copyright © William C. ChengAside: What are the implications of global connectivity?Societal issuesEconomic issuesSecurity issuesetc.Traffic data rateApplication input to network16Application Considerations Computer Communications - CSCI 551 Copyright © William C. ChengTraffic pattern (bursty or constant bit rate)Traffic target (multipoint or single destination, mobile orfixed)Delay sensitivityNetwork service delivered to applicationLoss sensitivityreliable file transferApplication examples:remote loginnetwork audionetwork videowebReliable file transfer17Application Examples Computer Communications - CSCI 551 Copyright © William C. ChengLoss sensitiveNot delay sensitive relative to round trip timesPoint-to-point or multipointBurstyRemote loginLoss sensitiveDelay sensitivesubject to interactive constraintscan tolerate up to several hundreds of millisecondsBurstyPoint to pointNetwork audioRelatively low bandwidthdigitized samples, packetizedDelay variance sensitiveLoss tolerant18Application Examples (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengPossibly multipoint, long duration sessionsnatural limit to number of simultaneous sendersCompressed audio, burstyNetwork videoHigh bandwidthCompressed video, burstyLoss tolerance function of compressionDelay tolerance a function of interactivityPossibly multipointLarger number of simultaneous sourcesWebTransactional trafficshort requests, possibly large responsesLoss (bug?) tolerantDelay sensitive19Application Examples (Cont...) Computer Communications - CSCI 551 Copyright © William C. Chenghuman interactivityPoint-to-point (multipoint is asynchronous)Applications that disrupt business as usual20Disruptive Applications Computer Communications - CSCI 551 Copyright © William C. ChengNot easy to predict: multicast case in pointWeb was arguably the first, and not many saw that comingNapster is the poster childGnutella, Kazaa, Morpheus, BitTorrent (?)Others? What’s next?21 Computer Communications - CSCI 551 Copyright © William C. Cheng Why A Single Network?can use excess capacity more efficientlyEfficiencycompare phone networks: voice calls, fax, modemsEase of introducing new applicationsto Internet: mail, remote login, file transfer, games, onlinetransactions, blogging, information retrieval, uploadsThe Global Network22 Computer Communications - CSCI 551 Copyright © William C. ChengGetting started23The Global Network Computer Communications - CSCI 551 Copyright © William C. ChengMetricsFailure modesHost configurationNetwork configurationISPa physical network cable (Ethernet, etc.)Host configuration needs:24Host Configuration Computer Communications - CSCI 551 Copyright © William C. Chengan IP addressa network maska gatewaya DNS server (and other servers)Automated with DHCPwires (from the phone or cable company)Network configuration needs:25A Network Computer Communications - CSCI 551 Copyright © William C. ChengRouter(s)a firewall?an ISP to connect to the Internetnetwork addresses (e.g., 192.168.1.xxx)serversa (big?) block of addressesISP needs:26An ISP Computer Communications - CSCI 551 Copyright © William C. Chengconnections to one or more other ISPs, peeringsmultiple routers, probably at exchange pointsservers for your users: mail, web, etc.servers for you: monitoring, etc.competent network admins (recommended)an AUP (Acceptable
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