計算機學校--英文講座-文庫吧
2025-11-09 12:15 本頁面
【正文】 ing and forwarding Introduct by Weifeng Sun Network layer 8/36 Connection setup ? 3rd important function in some work architectures: – ATM, frame relay, ? before datagrams flow, two end hosts and intervening routers establish virtual connection – routers get involved ? work vs transport layer connection service: – work: between two hosts (may also involve intervening routers in case of VCs) – transport: between two processes Introduct by Weifeng Sun Network layer 9/36 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: ? inorder datagram delivery ? guaranteed minimum bandwidth to flow ? restrictions on changes in interpacket spacing Introduct by Weifeng Sun Network layer 10/36 Network layer service models: Network Architecture Inter 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 ? Introduct by Weifeng Sun Network layer 11/36 Chapter 4: Network Layer ? 4. 1 Introduction ? Virtual circuit and datagram works ? What?s inside a router ? IP: Inter Protocol – Datagram format – IPv4 addressing – ICMP – IPv6 ? Routing algorithms – Link state – Distance Vector – Hierarchical routing ? Routing in the Inter – RIP – OSPF – BGP ? Broadcast and multicast routing Introduct by Weifeng Sun Network layer 12/36 Network layer connection and connectionless service ? datagram work provides worklayer connectionless service ? VC work provides worklayer connection service ? analogous to the transportlayer services, but: – service: hosttohost – no choice: work provides one or the other – implementation: in work core Introduct by Weifeng Sun Network layer 13/36 Virtual circuits ? call setup, teardown for each call before data can flow ? each packet carries VC identifier (not destination host address) ? every router on sourcedest path maintains “state” for each passing connection ? link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service) “sourcetodest path behaves much like telephone circuit” – performancewise – work actions along sourcetodest path Introduct by Weifeng Sun Network layer 14/3
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