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 D packets typically routed using destination host ID 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 4: Network Layer 4a-6
4: Network Layer 4a-6 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 typically routed using destination host ID 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 extented: Intserv diffserv o Chapter 6 4: Network Layer 4a-7
4: Network Layer 4a-7 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 extented: 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 4: Network Layer 4a-8
4: Network Layer 4a-8 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
Routing Routing protocol Goal: determine"good"path 5 (sequence of routers)thru network from source to dest B3-3 2 5 CA 2 Graph abstraction for routing algorithms O graph nodes are routers good"path o graph edges are o typically means minimum hysical links phy cost path o link cost: delay, $s cost o other defs possible or congestion level 4: Network Layer 4a-9
4: Network Layer 4a-9 Routing Graph abstraction for routing algorithms: graph nodes are routers graph edges are physical links link cost: delay, $ cost, or congestion level Goal: determine “good” path (sequence of routers) thru network from source to dest. Routing protocol A D E B C F 2 2 1 3 1 1 2 5 3 5 “good” path: typically means minimum cost path other def’s possible
Routing Algorithm classification Global or decentralized Static or dynamic? information? Static Global: o routes change slowly over o all routers have complete time topology link cost info Dynamic 0 link state"algorithms o routes change more quickly Decentralized o periodIc updaTe o router knows physically o in response to link cost connected neigh g bors link changes costs to neighbors g iterative process of computation exchange of info with neighbors o distance vector"algorithms 4: Network Layer 4a-10
4: Network Layer 4a-10 Routing Algorithm classification Global or decentralized information? Global: all routers have complete topology, link cost info “link state” algorithms Decentralized: router knows physicallyconnected neighbors, link costs to neighbors iterative process of computation, exchange of info with neighbors “distance vector” algorithms Static or dynamic? Static: routes change slowly over time Dynamic: routes change more quickly periodic update in response to link cost changes