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37 Pages

chapter1

Course: CNT 4007, Spring 2012
School: University of Florida
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Word Count: 1248

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4007 CNT Computer Networks - Chapter 1 : Overview JonathanC.L.Liu,Ph.D. DepartmentofComputer,Information ScienceandEngineering(CISE), UniversityofFlorida 1 Chapter 1: Introduction Overview: Ourgoal: whatstheInternet? getfeeland whatsaprotocol? terminology moredepth,detail networkedge;hosts,access laterincourse approach: useInternetas example net,physicalmedia networkcore:packet/circuit switching,Internetstructure performance:loss,delay, throughput protocollayers,service models 2 Whats the Internet: nuts and bolts view millionsofconnected PC server wireless laptop cellular handheld access points wired links router computingdevices: hosts=endsystems runningnetwork apps Mobilenetwork GlobalISP Homenetwork RegionalISP communicationlinks fiber,copper, radio,satellite transmissionrate =bandwidth Institutionalnetwork 3 Whats the Internet protocolscontrolsending, receivingofmsgs Mobilenetwork Internet:networkof networks Homenetwork GlobalISP e.g.,TCP,IP,HTTP,Skype, Ethernet looselyhierarchical publicInternetversusprivate intranet Internetstandards RegionalISP Institutionalnetwork RFC:Requestforcomments IETF:InternetEngineering TaskForce 4 Whats the Internet: a service view communication infrastructureenables distributedapplications: Web,VoIP,email,games, ecommerce,filesharing communicationservices providedtoapps: reliabledatadeliveryfrom sourcetodestination besteffort(unreliable) datadelivery 5 Whats a protocol? ahumanprotocolandacomputernetwork protocol: Hi TCPconnection request Hi TCPconnection response Gotthe time? Gethttp://www.ufl.edu/ 2:00 time <file> Q:Otherhumanprotocols? 6 Whats a protocol? humanprotocols: whatsthetime? Ihaveaquestion introductions specificmsgssent specificactions takenwhenmsgs received,orother events networkprotocols: machinesratherthan humans allcommunication activityinInternet governedbyprotocols protocolsdefineformat, orderofmsgssentand receivedamong networkentities,and actionstakenonmsg transmission,receipt 7 A closer look at network structure: networkedge: applicationsand hosts networkcore: routers networkof networks accessnetworks, physicalmedia: communication links 8 The network edge: endsystems(hosts): runapplicationprograms e.g.Web,email atedgeofnetwork client/servermodel clienthostrequests, receivesservicefrom alwaysonserver e.g.Webbrowser/server; emailclient/server peerpeermodel: minimal(orno)useof dedicatedservers 9 Access networks and physical media Q:Howtoconnectend systemstoedge router? residentialaccessnets institutionalaccess networks(school, company) mobileaccessnetworks Keepinmind: bandwidth(bitsper second)ofaccess network? sharedordedicated? 10 Residential access: point to point access Dialupviamodem upto56Kbpsdirectaccessto router(oftenless) Cantsurfandphoneatsame time:cantbealwayson DSL:digitalsubscriberline deployment:telephonecompany(typically) upto1Mbpsupstream(todaytypically<256kbps) upto8Mbpsdownstream(todaytypically<1Mbps) dedicatedphysicallinetotelephonecentraloffice 11 Digital Subscriber Lines Bandwidthversusdistancedover category3UTPforDSL. 12 Digital Subscriber Lines AtypicalADSLequipmentconfiguration. 13 Residential access: cable modems HFC:hybridfibercoax asymmetric:upto30Mbps downstream,2Mbpsupstream networkofcableandfiberattaches homestoISProuter homesshareaccesstorouter deployment:availableviacableTV companies 14 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 15 Cable Network Architecture: Overview Typically500to5,000homes cable headend cable distribution network (simplified) home 16 Cable Network Architecture: Overview server(s) cable headend cable distribution network home 17 Cable Network Architecture: Overview cable headend cable distribution network (simplified) home 18 Cable Network Architecture: Overview FDM(moreshortly): V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels cable headend cable distribution network home 19 Company local access: area networks company/univlocalarea network(LAN)connects endsystemtoedge router Ethernet: 10Mbs,100Mbps, 1Gbps,10Gbps Ethernet modernconfiguration: endsystemsconnect intoEthernetswitch 20 Wireless access networks sharedwirelessaccess networkconnectsend systemtorouter viabasestationakaaccess point wirelessLANs: 802.11b/g(WiFi):11or54 router base station Mbps widerareawirelessaccess mobile hosts ~1Mbpsovercellularsystem (EVDO,HSDPA) WiMAX(upto100Mbps) overwidearea 21 Home networks Typicalhomenetworkcomponents: DSLorcablemodem router/firewall/NAT Ethernet wirelessaccess point to/from cable headend cable modem router/ firewall Ethernet wireless laptops wireless access point 22 Physical Media Bit:propagatesbetween transmitter/rcvrpairs physicallink:whatlies betweentransmitter& receiver guidedmedia: signalspropagateinsolid media:copper,fiber,coax TwistedPair(TP) twoinsulatedcopper wires Category3:traditional phonewires,10Mbps Ethernet Category5: 100MbpsEthernet unguidedmedia: signalspropagatefreely,e.g., radio 23 Physical Media: coax, fiber Coaxialcable: Fiberopticcable: twoconcentriccopper conductors bidirectional baseband: glassfibercarryinglight pulses,eachpulseabit highspeedoperation: broadband: lowerrorrate:repeaters spacedfarapart;immune toelectromagneticnoise singlechanneloncable legacyEthernet multiplechannelson cable HFC highspeedpointtopoint transmission(e.g.,10s 100sGps) 24 Physical media: radio signalcarriedin electromagnetic spectrum nophysicalwire bidirectional propagation environmenteffects: reflection obstructionbyobjects interference Radiolinktypes: terrestrialmicrowave e.g.upto45Mbpschannels LAN(e.g.,Wifi) 11Mbps,54Mbps widearea(e.g.,cellular) 3Gcellular:~1Mbps satellite Kbpsto45Mbpschannel(or multiplesmallerchannels) 270msecendenddelay geosynchronousversuslow altitude 25 The Network Core meshof interconnectedrouters thefundamental question:howcandata betransferredthrough thenet? circuitswitching: dedicatedcircuitper call:telephonenet packetswitching: datasentthrunetin discretechunks 26 Network Core: Circuit Switching Endendresources reservedforcall linkbandwidth, switchcapacity dedicated resources:no sharing circuitlike (guaranteed) performance callsetuprequired 27 Network Core: Circuit Switching networkresources (e.g.,bandwidth) dividedinto pieces piecesallocatedto calls resourcepieceidleif notusedbyowning call(nosharing) dividinglink bandwidthinto pieces frequencydivision timedivision 28 Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time 29 Time Division Multiplexing TheT1carrier(1.544Mbps). 30 Time Division Multiplexing (3) MultiplexingT1streamsintohigher carriers. 31 32 33 Network Core: Packet Switching eachendenddatastream resourcecontention: dividedintopackets aggregateresource userA,Bpacketsshare demandcanexceed networkresources amountavailable eachpacketusesfulllink congestion:packets bandwidth resourcesusedasneeded queue,waitforlink Bandwidthdivisioninto pieces Dedicatedallocation Resourcereservation use storeandforward: packetsmoveone hopatatime Nodereceivescomplete packetbeforeforwarding 34 Packet Switching: Statistical Multiplexing 100Mb/s Ethernet A B C statistical multiplexing 1.5Mb/s queueofpackets waitingforoutput link D E SequenceofA&Bpacketsdoesnothavefixed pattern,bandwidthsharedondemand statisticalmultiplexing. 35 Packet switching versus circuit switching Packetswitchingallowsmoreusers!! 1Mb/slink eachuser: 100kb/swhenactive active10%oftime circuitswitching: 10users Nusers 1Mbpslink packetswitching: with35users, probability>10 activeatsametime islessthan.0004 Q:howdidwegetvalue0.0004? 36 Packet switching versus circuit switching Ispacketswitchingaslamdunkwinner? Greatforburstydata resourcesharing simpler,nocallsetup Excessivecongestion:packetdelayandloss protocolsneededforreliabledatatransfer, congestioncontrol Q:Howtoprovidecircuitlikebehavior? bandwidthguaranteesneededfor audio/videoapps stillanunsolvedproblem 37

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