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Network Layer 4-1Chapter 4Network LayerA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWRAll material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights ReservedComputer Networking: A Top Down Approach 4thedition. Jim Kurose, Keith RossAddison-Wesley, July 2007.Network Layer 4-2Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What‟s inside a router 4.4 IP: Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 Broadcast and multicast routingNetwork Layer 4-3Network 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 everyhost, router router examines header fields in all IP packets passing through itapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalNetwork Layer 4-4Two Key Network-Layer Functionsforwarding:move packets from router‟s input to appropriate router outputrouting: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 4-51230111value in arrivingpacket’s headerrouting algorithmlocal forwarding tableheader valueoutput link01000101011110013221Interplay between routing and forwardingRouting Algorithm• Static: Human configures•Centralized: Algorithm is executed on central site and downloaded•Decentralized: Runs on each routerNetwork Layer 4-6Connection setup 3rdimportant function in somenetwork architectures: ATM, frame relay, X.25 before datagrams flow, two end hosts andintervening routers establish virtual connection routers get involved network vs transport layer connection service: network: between two hosts (may also involve intervening routers in case of VCs) transport: between two processesNetwork Layer 4-7Network service modelQ: What service modelfor “channel” transporting packets from sender to receiver?Example services for individual packets: Guaranteed delivery Guaranteed delivery with less than 40 msec delayExample services for a flow of packets: In-order packet delivery Guaranteed minimum bandwidth to flow Guaranteed maximum jitter: time between transmission of two successive packets is equal to the time betweeen their receipt at the distination or no more than a specified value SecurityNetwork Layer 4-8Network layer service models:NetworkArchitectureInternetATMATMServiceModelbest effortCBRABRBandwidthnoneconstantrateguaranteed minimumLossnoyesnoOrdernoyesyesTimingnoyesnoCongestionfeedbackno (inferredvia loss)noCongestionyesGuarantees ?Constant Bit Rate (CBR)Available Bit Rate (ABR)Asynchronous Transfer Mode (ATM) Protocol Compromise between the rigidity of the telecommunication synchronous architecture and packet network‟s unpredictable load behavior Used by telecommunication companies as a broadband carrier for ISDN networks Viewed by the computer industry as a strong candidate for high-speed LAN networkingNetwork Layer 4-9Network Layer 4-10Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What‟s inside a router 4.4 IP: Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 Broadcast and multicast routingNetwork Layer 4-11Network layer connection and connection-less service Datagram Network provides network-layer connectionless service Virtual Circuit Network provides network-layer connection service Analogous to the transport-layer services, but: service: host-to-host implementation: in network coreNetwork Layer 4-12Virtual circuits Source to destination path behaves much like a telephone circuit Call setup, teardown for each call beforedata can flow Each packet carries VC identifier (not destination host address)Everyrouter on source-dest path maintains “state” for each passing connection Link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service)Network Layer 4-13VC 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 VC number (rather than dest address) VC number can be changed on each link. New VC number comes from forwarding tableNetwork Layer 4-14Forwarding table122232123VC numberinterfacenumberIncoming interface Incoming VC # Outgoing interface Outgoing VC #1 12 3 222 63 1 18 3 7 2 171 97 3 87… … … …Forwarding table innorthwest router:Routers maintain connection state information!VC numbersNetwork Layer 4-15 Why doesn‟t a
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