《计算机网络》课程PPT教学课件（自顶向下方法，英文第三版）第四章 Network Layer

Chapter 4 Network Layer computer networking James F.Kurose Keith W.Ross A 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 Computer Networking: (including this one)and slide content to suit your needs.They obviously A Top Down Approach represent a lot of work on our part.In return for use,we only ask the following: Featuring the Internet, If you use these slides (e.g.,in a class)in substantially unaltered form, 3rd edition that you mention their source(after all,we'd like people to use our book!) f you post any slides in substantially unaltered form on a ww site,that Jim Kurose,Keith Ross you note that they are adapted from(or perhaps identical to)our slides,and note our copyright of this material. Addison-Wesley,July 2004. Thanks and enjoy!JFK/KWR All material copyright 1996-2006 J.F Kurose and K.W.Ross,All Rights Reserved Network Layer 4-1

Network Layer 4-1 Chapter 4 Network Layer Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. A 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/KWR All material copyright 1996-2006 J.F Kurose and K.W. Ross, All Rights Reserved

Chapter 4:Network Layer Chapter goals: Ounderstand principles behind network layer services: o network layer service models o forwarding versus routing o how a router works o routing (path selection) o dealing with scale o advanced topics:IPv6,mobility instantiation,implementation in the Internet Network Layer 4-2

Network Layer 4-2 Chapter 4: Network Layer Chapter goals:  understand principles behind network layer services:  network layer service models  forwarding versus routing  how a router works  routing (path selection)  dealing with scale  advanced topics: IPv6, mobility  instantiation, implementation in the Internet

Chapter 4:Network Layer ▣4.1 Introduction 4.5 Routing algorithms 4.2 Virtual circuit and o Link state datagram networks o Distance Vector ▣4.3What's inside a o Hierarchical routing router 4.6 Routing in the 4.4 IP:Internet Internet Protocol O RIP o OSPF o Datagram format o IPv4 addressing oBGP ICMP ▣4.7 Broadcast and IPv6 multicast routing Network Layer 4-3

Network Layer 4-3 Chapter 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 routing

Network layer transport segment from sending to receiving host applicatior TransporT ▣on sending side network data link physical network encapsulates segments network data link network data link physical data link physical physical into datagrams network data link on rcving side,delivers physical network data link segments to transport physical network layer network data link data link physical physical network layer protocols network data link application in every host,router physical transport network data link Router examines header physical fields in all IP datagrams passing through it Network Layer 4-4

Network Layer 4-4 Network 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 it network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical application transport network data link physical

Two Key Network-Layer Functions ▣forwarding:.move analogy: packets from router's input to appropriate ▣routing:process of router output planning trip from source to dest ▣routing:determine route taken by forwarding:process packets from source of getting through to dest. single interchange o routing algorithms Network Layer 4-5

Network Layer 4-5 Two Key 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 algorithms analogy:  routing: process of planning trip from source to dest  forwarding: process of getting through single interchange

Interplay between routing and forwarding routing algorithm local forwarding table header value output link 0100 0101 2 0111 1001 value in arriving packet's header 0111 Network Layer 4-6

Network Layer 4-6 1 2 3 0111 value in arriving packet’s header routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 Interplay between routing and forwarding

Connection setup 3rd important function in some network architectures: ATM,frame relay,X.25 before datagrams flow,two end hosts and intervening routers establish virtual connection o routers get involved network vs transport layer connection service: o network:between two hosts(may also involve inervening routers in case of VCs) o transport:between two processes Network Layer 4-7

Network Layer 4-7 Connection setup  3 rd important function in some network architectures:  ATM, frame relay, X.25  before datagrams flow, two end hosts and intervening routers establish virtual connection  routers get involved  network vs transport layer connection service:  network: between two hosts (may also involve inervening routers in case of VCs)  transport: between two processes

Network service model Q:What service model for "channel"transporting datagrams from sender to receiver? Example services for Example services for a individual datagrams: flow of datagrams: ▣guaranteed delivery in-order datagram ▣guaranteed delivery delivery with less than 40 msec ▣guaranteed minimum delay bandwidth to flow ▣restrictions on changes in inter- packet spacing Network Layer 4-8

Network Layer 4-8 Network service model Q: What service model for “channel” transporting datagrams from sender to receiver? Example services for individual datagrams:  guaranteed delivery  guaranteed delivery with less than 40 msec delay Example services for a flow of datagrams:  in-order datagram delivery  guaranteed minimum bandwidth to flow  restrictions on changes in inter￾packet spacing

Network layer service models: Network Service Guarantees Congestion Architecture Model Bandwidth Loss Order Timing feedback Internet best effort none no no no no(inferred via loss) ATM CBR constant yesyes yes no rate congestion ATM VBR guaranteed yes yes yes no rate congestion ATM ABR guaranteed no yes no yes minimum ATM UBR none no yes no no Network Layer 4-9

Network Layer 4-9 Network layer service models: Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees ?

Chapter 4:Network Layer ▣4.1 Introduction 4.5 Routing algorithms 4.2 Virtual circuit and o Link state datagram networks o Distance Vector 4.3 What's inside a o Hierarchical routing router 4.6 Routing in the ▣4.4IP:Internet Internet Protocol o RIP o Datagram format o OSPF o IPv4 addressing o BGP o ICMP ▣4.7 Broadcast and o IPv6 multicast routing Network Layer 4-10

Network Layer 4-10 Chapter 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 routing