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U of I CS 438 - Packet Forwarding

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Packet ForwardingNow Arriving at Layer 3Network Layers and RoutersRouter DesignForwardingSwitching and ForwardingForwarding with DatagramsSlide 8Routing TableSlide 10Slide 11Traceroute ExampleDatagramsForwarding with Virtual CircuitsVirtual CircuitsSlide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Forwarding with source routingForwarding with Source RoutingSlide 27ATMSlide 29ATM DetailsATM CellsATM RationaleSlide 33Slide 34Slide 35Slide 36Slide 37ATM and LANsStructure of LANEATM Local Area Network Emulation (LANE)Slide 41ATM/LANE Protocol LayersPacket Forwarding01/14/19 CS/ECE 438 - UIUC, Fall 2007 2Now Arriving at Layer 3… although layer 2 switches and layer 3 routers are similar in many ways… and ATM/Virtual Circuits are used at layer 2 these days01/14/19 CS/ECE 438 - UIUC, Fall 2007 3Network Layers and RoutersApplicationPresentationPhysicalTransportSessionData LinkNetworkPhysicalData LinkNetworkApplicationPresentationPhysicalTransportSessionData LinkNetworkHostRouter01/14/19 CS/ECE 438 - UIUC, Fall 2007 4Router DesignInput PortInput PortInput PortInput PortInput PortInput PortOutput PortOutput PortOutput PortOutput PortOutput PortOutput PortSwitch Fabric01/14/19 CS/ECE 438 - UIUC, Fall 2007 5ForwardingForwarding AlgorithmConsult packet headerConsult forwarding tablesDecide on output portThree general typesDatagram forwardingVirtual CircuitsSource RoutingDiffer by contents of header and tables01/14/19 CS/ECE 438 - UIUC, Fall 2007 6Switching and ForwardingForwardingThe task of specifying an appropriate output port for a packetDatagram Virtual Circuit SwitchingSource RoutingEach packet contains enough information for a switch to determine the correct output portLaterBuilding forwarding tables – routing.Packet HeaderOutput Port Specification01/14/19 CS/ECE 438 - UIUC, Fall 2007 7Forwarding with DatagramsConnectionlessEach packet travels independentlySwitchTranslates global address to output portMaintains table of translationsUsed in traditional data networksi.e., Internet01/14/19 CS/ECE 438 - UIUC, Fall 2007 8Forwarding with DatagramsHost AHost GHost DHost EHost CHost BHost F 012301230123012301/14/19 CS/ECE 438 - UIUC, Fall 2007 9Routing TableABCDEFGABCDEFGABCDEFGABCDEFG’s Table ’s Table ’s Table ’s TableEach switch maintains a routing table that translates a host name to an output portAGDECBF0123012301230123011111330112233312333000013001/14/19 CS/ECE 438 - UIUC, Fall 2007 10Forwarding with DatagramsA  EDATAEA sends:C  FDATAFC sends:B  EDATAEB sends:F  GDATAGF sends:A  HDATAHA sends:What happens to the last packet?AGDECBF012301230123012301/14/19 CS/ECE 438 - UIUC, Fall 2007 11Forwarding with DatagramsAnalogous to following signsRequires globally unique addressesRouting is decentralizedA router follows global routing algorithmsTwo packets usually take the same path but…Each router can change its mind at any time01/14/19 CS/ECE 438 - UIUC, Fall 2007 12Traceroute ExampleFrom last year’s solutionstraceroute www.scott.aq traceroute to www.scott.aq (203.167.246.34), 30 hops max, 40 byte packets 1 uiuc-ewsl-vlan1.gw.uiuc.edu (130.126.160.1) 0.425 ms 0.213 ms 0.319 ms 2 …13 ae-0-0.bbr1.Washington1.Level3.net (64.159.0.229) 21.946 ms as-2-0.bbr2.Washington1.Level3.net (209.247.10.130) 21.351 ms 21.280 ms01/14/19 CS/ECE 438 - UIUC, Fall 2007 13DatagramsAdvantagesRoutes around failuresCan send traffic immediatelyDisadvantagesHeader requires full unique addressMight not be possible to deliver packetSuccessive packets may not follow the same routeGlobal address to path translations requires significant storage01/14/19 CS/ECE 438 - UIUC, Fall 2007 14Forwarding with Virtual CircuitsConnection orientedRequires explicit setup and teardownPackets follow established routeWhy support connections in a network?Useful for service notionsImportant for telephonySwitchTranslates virtual circuit ID on incoming link to virtual circuit ID on outgoing linkCircuit Ids can be per-link or per-switchUsed in ATM01/14/19 CS/ECE 438 - UIUC, Fall 2007 15Virtual CircuitsPacket header stores:Virtual Circuit IDRouter stores:Table of how to forward packets for each virtual circuitNote: VCID need not be globalAssign a VCID to a circuit for each link-link pair01/14/19 CS/ECE 438 - UIUC, Fall 2007 16Forwarding with Virtual CircuitsSet upA virtual circuit identifier (VCI) is assigned to the circuit for each link it traversesVCI is locally significant<incoming port, incoming VCI> uniquely identifies VCSwitchMaintains a translation table from <incoming port, incoming VCI> to <outgoing port, outgoing VCI>Permanent Virtual Circuits (PVC)Long-livedSwitch Virtual Circuits (SVC)Uses signaling to establish VC01/14/19 CS/ECE 438 - UIUC, Fall 2007 17Forwarding with Virtual CircuitsPort INVCI INPort OUTVCI OUTPort INVCI INPort OUTVCI OUTPort INVCI INPort OUTVCI OUT Table entries after A E connection is set0100VCI OUTPort OUTVCI INPort IN0203VCI OUTPort OUTVCI INPort IN0100VCI OUTPort OUTVCI INPort INAGDECBF0123012301230123AE01/14/19 CS/ECE 438 - UIUC, Fall 2007 18Forwarding with Virtual CircuitsA simple example setup protocolEach host and switch maintains per-linklocal variable for VCI assignmentWhen setup frame leaves host/switchAssign outgoing VCIIncrement assignment counterport and circuit id combination is uniqueswitches maintain translation table fromincoming port/VCI pair tooutgoing port/VCI pair01/14/19 CS/ECE 438 - UIUC, Fall 2007 19Forwarding with Virtual CircuitsAssumptionsCircuits are simplexOn a duplex link, the same VCI can be used for two circuits, one in each directionThe same VCI can be used on different ports of the same switchAt setup, the lowest available VCI is used01/14/19 CS/ECE 438 - UIUC, Fall 2007 20Forwarding with Virtual CircuitsHost AHost GHost DHost EHost CHost BHost F 23012123123Set up circuit:A  E1 3000Setup Message: Dest = EHost EVCI = ?Setup Message: Dest = E<0,0>  <1,?> Setup Message: Dest = E<3,0>  <2,?>Setup Message: Dest = E<0,0>  <1,?>01/14/19 CS/ECE 438 - UIUC, Fall 2007 21Forwarding with Virtual CircuitsHost AHost GHost DHost EHost CHost BHost F 23012123123Set up circuit:A  E1 3000ACK


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U of I CS 438 - Packet Forwarding

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