西南师范大学：《计算机网络》课程教学资源（PPT课件讲稿，英文版）Chapter 4 Network Layer

Chapter 4 Network Layer Computer Networking A Top Down Approach The powerpoint slides are based on the material Featuring the Internet 2nd edition provided by Jim Kurose, Keith Ros J F Kurose and K.W. Ross Addison-Wesley, Juf 2002 Network Layer 4-1

Network Layer 4-1 Chapter 4 Network Layer Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002. The PowerPoint Slides are based on the material provided by J.F Kurose and K.W. Ross

Chapter 4: Network Layer Chapter goals: Overview: o understand principles o network layer services behind network layer D routing principles: path services: selection o routing(path selection) o hierarchical routing o dealing with scale g IP o how a router works o advanced topics: IPv6 o Internet routing protocols mobility o intra-domain g instantiation and o inter-domain implementation in the o what's inside a router? Internet 了TPV6 o mobility Network Layer 4-2

Network Layer 4-2 Chapter 4: Network Layer Chapter goals:  understand principles behind network layer services:  routing (path selection)  dealing with scale  how a router works  advanced topics: IPv6, mobility  instantiation and implementation in the Internet Overview:  network layer services  routing principles: path selection  hierarchical routing  IP  Internet routing protocols  intra-domain  inter-domain  what’s inside a router?  IPv6  mobility

Chapter 4 roadmap 4. 1 Introduction and Network Service Models 4.2 Routing Principles 4.3 Hierarchical Routing 4.4 The Internet(Ip) protocol 4.5 Routing in the Internet 4.6 What's Inside a router 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility Network Layer 4-3

Network Layer 4-3 Chapter 4 roadmap 4.1 Introduction and Network Service Models 4.2 Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.5 Routing in the Internet 4.6 What’s Inside a Router 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility

Network layer functions o transport packet from pplication sending to receiving hosts g network layer protocols in network eve ery host, router data link physical data link hysical three important functions ●●●口 data link o path determination: route data link lyrical taken by packets from source to dest. routing algorithms data link data link ysical o forwarding: move packets from router 's input to appropriate router output data link o call setup: some network architectures require router call setup along path before data flows Network Layer 4-4

Network Layer 4-4 Network layer functions  transport packet from sending to receiving hosts  network layer protocols in every host, router three important functions:  path determination: route taken by packets from source to dest. Routing algorithms  forwarding: move packets from router’s input to appropriate router output  call setup: some network architectures require router call setup along path before data flows 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

Network service model Q: What service model for channel transporting packets The most important abstraction provided from sender to by network layer receiver? s o guaranteed bandwidth? virtual circuit t o preservation of inter-packet or timing(no jitter)? datagram? go loss-free delivery o in-order delivery? 5 o congestion feedback to sender? Network le 45

Network Layer 4-5 Network service model Q: What service model for “channel” transporting packets from sender to receiver?  guaranteed bandwidth?  preservation of inter-packet timing (no jitter)?  loss-free delivery?  in-order delivery?  congestion feedback to sender? ? ? ? virtual circuit or datagram? The most important abstraction provided by network layer:

Virtual circuits source-to-dest path behaves much like telephone circuit o performance-WIse o network actions along source-to-dest path o call setup, teardown for each call before data can flow D each packet carries VC identifier(not destination host ID) o every router on source-dest path maintains "state"for each passing connection o transport-layer connection only involved two end systems o link, router resources(bandwidth, buffers)may be allocated to vc o to get circuit-like perf Network Layer 4-6

Network Layer 4-6 Virtual circuits  call setup, teardown for each call before data can flow  each packet carries VC identifier (not destination host ID)  every router on source-dest path maintains “state” for each passing connection  transport-layer connection only involved two end systems  link, router resources (bandwidth, buffers) may be allocated to VC  to get circuit-like perf. “source-to-dest path behaves much like telephone circuit”  performance-wise  network actions along source-to-dest path

Virtual circuits: signaling protocols D used to setup maintain teardown Vc O used in ATM, frame-relay, X25 g not used in today' s Internet applICaTion transport 5 Data flow begins 6. Receive data application network 4. Call connected transpon↑ 3. Accept ce data link 1 Initiate call network 2. incoming c data link physIca physical Network le 4-7

Network Layer 4-7 Virtual circuits: signaling protocols  used to setup, maintain teardown VC  used in ATM, frame-relay, X.25  not used in today’s Internet application transport network data link physical application transport network data link physical 1. Initiate call 2. incoming call 4. Call connected 3. Accept call 5. Data flow begins 6. Receive data

Datagram networks: the Internet model o no call setup at network layer routers: no state about end-to-end connections o no network-level concept of "connection O packets forwarded using destination host address o packets between same source-dest pair may take different paths applIcaTion fransport application network fransport data link 1.Send data neTwor k 2 Receive data data link physical t physical I )< Network Layer 4-8

Network Layer 4-8 Datagram networks: the Internet model  no call setup at network layer  routers: no state about end-to-end connections  no network-level concept of “connection”  packets forwarded using destination host address  packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data

Network layer service models: Network Service Guarantees Congestion Architecture Model Bandwidth Loss Order Timing feedback Internet best effort none no no no(inferred via loss) ATM CBR constant yes yes yes no rate congestion ATM VBR guaranteed yesyes yes no rate congestion ATM ABR guaranteed no yes no yes minimum ATM UBR none yes no no o Internet model being extended: Intserv Diffserv o Chapter 6 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 ?  Internet model being extended: Intserv, Diffserv  Chapter 6

Datagram or Vc network why? Internet ATM o data exchange among D evolved from telephony computers o human conversation: o elastic"service. no strict timing req o strict timing, reliability requirements 口"smar+" end systems (computers) o need for guaranteed service o can adapt, perform 口"dumb" end systems control, error recovery o telephones o simple inside network complexity at edge o complexity inside o many link types network o different characteristics o uniform service difficult Network Layer 4-10

Network Layer 4-10 Datagram or VC network: why? Internet  data exchange among computers  “elastic” service, no strict timing req.  “smart” end systems (computers)  can adapt, perform control, error recovery  simple inside network, complexity at “edge”  many link types  different characteristics  uniform service difficult ATM  evolved from telephony  human conversation:  strict timing, reliability requirements  need for guaranteed service  “dumb” end systems  telephones  complexity inside network