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