Datagram or VC network:why? Internet (datagram) ATM(VC) data exchange among evolved from telephony computers ▣human conversation: o "elastic"service,no strict timing req. o strict timing,reliability requirements "smart"end systems o need for guaranteed (computers) service o can adapt,perform control,error recovery "dumb"end systems o simple inside network, o telephones complexity at "edge" o complexity inside network many link types o different characteristics o uniform service difficult Network Layer 4-19 Network Layer 4-19 Datagram or VC network: why? Internet (datagram)  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 (VC)  evolved from telephony  human conversation:  strict timing, reliability requirements  need for guaranteed service  “dumb” end systems  telephones  complexity inside network