Data Communication and NetworksSwitching NetworksTechnologySimple Switched NetworkCircuit SwitchingCircuit Switching - IssuesPacket SwitchingBasic OperationUse of PacketsNetwork layerKey Network-Layer FunctionsSlide 12Connection setupNetwork service modelNetwork layer service models:Virtual circuit vs. datagram networksNetwork layer connection and connection-less serviceVirtual circuitsVC implementationForwarding tableVirtual circuits: signaling protocolsDatagram networksSlide 23Longest prefix matchingDatagram or VC network: why?IP: Internet ProtocolThe Internet Network layerIP Addressing: introductionSubnetsSlide 30Slide 31IP addressing: CIDRIP datagram formatIP Fragmentation & ReassemblyIP Fragmentation and ReassemblyNAT: Network Address TranslationSlide 37Slide 38Slide 39Slide 40Network Layer 4-1Data Communication and NetworksLecture 6Networks: Part 1Circuit Switching, Packet Switching, The Network LayerOctober 13, 2005Network Layer 4-2Switching NetworksLong distance transmission is typically done over a network of switched nodesNodes not concerned with content of dataEnd devices are stationsComputer, terminal, phone, etc.A collection of nodes and connections is a communications networkData routed by being switched from node to nodeNetwork Layer 4-3TechnologyTwo different switching technologiesCircuit switchingPacket switchingNetwork Layer 4-4Simple Switched NetworkNetwork Layer 4-5Circuit SwitchingDedicated communication path between two stations (during conversation)Three phasesEstablishTransferDisconnectMust have switching capacity and channel capacity to establish connectionMust have intelligence to work out routingNetwork Layer 4-6Circuit Switching - IssuesCircuit switching is inefficient (designed for voice)Resources dedicated to a particular callMuch of the time a data connection is idleData rate is fixed•Both ends must operate at the same rateSet up (connection) takes timeOnce connected, transfer is transparentNetwork Layer 4-7Packet SwitchingNetwork Layer 4-8Basic OperationData transmitted in small packetsTypically 1000 octetsLonger messages split into series of packetsEach packet contains a portion of user data plus some control infoControl infoRouting (addressing) infoPackets are received, stored briefly (buffered) and passed on to the next nodeStore and forwardNetwork Layer 4-9Use of PacketsNetwork Layer 4-10Network layertransport segment from sending to receiving host on sending side encapsulates segments into datagramson rcving side, delivers segments to transport layernetwork layer protocols in every host, routerRouter examines header fields in all IP datagrams passing through itnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalNetwork Layer 4-11Key Network-Layer Functionsforwarding: move packets from router’s input to appropriate router outputrouting: determine route taken by packets from source to dest. Routing algorithmsanalogy:routing: process of planning trip from source to destforwarding: process of getting through single interchangeNetwork Layer 4-121230111value in arrivingpacket’s headerrouting algorithmlocal forwarding tableheader valueoutput link01000101011110013221Interplay between routing and forwardingNetwork Layer 4-13Connection setup3rd important function in some network architectures:ATM, frame relay, X.25Before datagrams flow, two hosts and intervening routers establish virtual connectionRouters get involvedNetwork and transport layer cnctn service:Network: between two hostsTransport: between two processesNetwork Layer 4-14Network service modelQ: What service model for “channel” transporting datagrams from sender to rcvr?Example services for individual datagrams:guaranteed deliveryGuaranteed delivery with less than 40 msec delayExample services for a flow of datagrams:In-order datagram deliveryGuaranteed minimum bandwidth to flowRestrictions on changes in inter-packet spacingNetwork Layer 4-15Network layer service models:NetworkArchitectureInternetATMATMATMATMServiceModelbest effortCBRVBRABRUBRBandwidthnoneconstantrateguaranteedrateguaranteed minimumnoneLossnoyesyesnonoOrdernoyesyesyesyesTimingnoyesyesnonoCongestionfeedbackno (inferredvia loss)nocongestionnocongestionyesnoGuarantees ?Network Layer 4-16Virtual circuit vs. datagram networksNetwork Layer 4-17Network layer connection and connection-less serviceDatagram network provides network-layer connectionless serviceVC network provides network-layer connection serviceAnalogous to the transport-layer services, but:Service: host-to-hostNo choice: network provides one or the otherImplementation: in the coreNetwork Layer 4-18Virtual circuitscall setup, teardown for each call before data can floweach packet carries VC identifier (not destination host address)every router on source-dest path maintains “state” for each passing connectionlink, router resources (bandwidth, buffers) may be allocated to VC“source-to-dest path behaves much like telephone circuit”performance-wisenetwork actions along source-to-dest pathNetwork Layer 4-19VC implementationA VC consists of:1. Path from source to destination2. VC numbers, one number for each link along path3. Entries in forwarding tables in routers along pathPacket belonging to VC carries a VC number.VC number must be changed on each link.New VC number comes from forwarding tableNetwork Layer 4-20Forwarding table122232123VC numberinterfacenumberIncoming interface Incoming VC # Outgoing interface Outgoing VC #1 12 2 222 63 1 18 3 7 2 171 97 3 87… … … …Forwarding table innorthwest router:Routers maintain connection state information!Network Layer 4-21Virtual circuits: signaling protocolsused to setup, maintain teardown VCused in ATM, frame-relay, X.25not used in today’s Internetapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysical1. Initiate call2. incoming call3. Accept call4. Call connected5. Data flow begins6.