L9: Intro Network Systems6.033 Spring 2007http://web.mit.edu/6.033Slides from many folksWhat have you seen so far?MapReduceCoping with bottlenecksPerformanceEraser and UnixClient/service with in a computerOperating systemsX windowsEnforced modularityClient/service designFile system name spaceGluing systemsNaming systemsHierarchyTherac-25ComplexityModularityDtechnology/dtSystemsClient/service using network•Sharing irrespective of geography•Strong modularity through geographic separationOSOSclientserverrequestnetworkNetwork is a system too!•Network consists of many networks, many links, many switches•Internet is a case study of successful network systemdomain-1domain-2domain-3Today’ s topic: challenges•Economical:•Universality•Topology, Sharing, Utilization•Organizational•Routing, Addressing, Packets, Delay•Best-effort contract•Physical•Errors, speed of light, wide-range of parametersCircuit SwitchingDATACaller CalleeBoston SwitchLA Switchpropagation delay between caller and and Boston switchprocessing delay at switch•It’ s the method used by the telephone network•A call has three phases:Establish circuit from end-to-end (“ dialing” ),Communicate,Close circuit (“ tear down” ).•If circuit not available: “ busy signal”(1)(2)(3)SwitchIsochronous Multiplexing/Demultiplexing•A time interval is divided into n frames•Each frame carries the data of a particular conversation •E.g., frame 0 belongs to the red conversation0 1 234 5 0 1 234 5frames = One way for sharing a link is TDM:intervalCircuit Switching•Assume link capacity is C bits/sec•Each communication requires R bits/sec•#frames = C/R•Maximum number of concurrent communications is C/R•What happens if we have more than C/R communications? •What happens if the a communication sends less/more than R bits/sec? Design is unsuitable for bursty communicationsPacket Switching•Used in the Internet•Data is sent in Packets (header contains control info, e.g., source and destination addresses)•Per-packet routing•At each node the entire packet is received, buffered, and then forwarded)•No capacity is allocated Header DataPacket 1Packet 2Packet 3Packet 1Packet 2Packet 3Packet 1Packet 2Packet 3processing delay of Packet 1 at Node 2propagationdelay betweenHost 1 & Node 2 transmission time of Packet 1at Host 1Host 1Host 2switch 1 switch 2SwitchAsynchronous Multiplexing/Demultiplexing•Multiplex using a queue•Switch need memory/buffer•Demultiplex using information in packet header•Header has destination •Switch has a forwarding table that contains information about which link to use to reach a destinationQueueAggregate Internet Traffic Smooths5-min average traffic rate at an MIT-CSAIL routerMax In:12.2Mb/s Avg. In: 2.5Mb/sMax Out: 12.8Mb/s Avg. Out: 3.4 Mb/sStatistical multiplexingBest EffortNo Guarantees:•Variable Delay (jitter)•Variable rate•Packet loss•Duplicates•ReorderingNetworks are heterogeneousLink technologyBits/s1000100001000001E+061E+071E+081E+091E+101E+11Tel modemWireless CDPDTel modemTel. modem2.5G wirelessBluetooth wirelessCable modem / DSLT1802.11 baseEthernetInfrared802.11b wirelessT3802.11a wirelessFast EthernetGig EthernetOC48 opticalOC192c optical10G EthernetOC768d(technology)/dt for networksMoore’ s Law2x / 18 monthsHighest Link Capacity2x / 7 monthsAggregate Internet Traffic2x / 12 months1101001,00010,000100,0001,000,0001980 1983 1986 1989 1992 1995 1998 2001Normalized Growth since 1980Speed of light0x / 18 months!Bits/s per dollar2x / 79 months(crude estimate)# Internet hosts2x / 13.3 monthsThanks to Nick Mckeown @ Stanford for some of these data pointsPlan for studying network systemsNATs7.FCongestion controlNetwork file system7.EEnd-to-end reliabilityInternet routing7.DRoutingEnd-to-end7.B+CLayeringEthernet7.ASharing and
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