internetworkingibasicsapril13,2000(編輯修改稿)
2024-11-29 17:40 本頁面
【文章內(nèi)容簡介】 n be dropped, latencies vary ? Homogeneity –can only support works with identical frame headers (., Ether/FDDI) –however, can connect different speed Ethers ? Scalability –tens of works only 187。bridges forward all broadcast frames 187。increased latency CS 213 S’00 – 17 – Interworking with application gateways application gateways (g in the figure) connect different works for particular applications. Example: ? User on host x posts news item to gateway machine on work A. ? Gateway on A passes item (along with others) to gateway B. ? User on host y reads message from gateway on B. g x g y Network A Network B phone system CS 213 S’00 – 18 – Interworking with application gateways host on work B use news application data link physical application data link modem phone physical Application gateway on work B transport work Gateway program Application gateway on work A CS 213 S’00 – 19 – Interworking with application gateways: Pros and cons Pros ? Heterogeneous –can connect different types of works ? Simple –modems + gateway software Cons ? Not generalpurpose –each solution is applicationspecific CS 213 S’00 – 20 – Interworking with routers Def: An interwork (inter for short) is an arbitrary collection of physical works interconnected by routers to provide some sort of hosttohost packet delivery service. inter host host host host CS 213 S’00 – 21 – Building an inter X Y Z work 2 (ECE) adapter adapter adapter A B C work 1 (SCS) adapter adapter adapter We start with two separate, unconnected puter works (subs), which are at different locations, and possibly built by different vendors. Ether ATM Question: How to present the illusion of one work? CS 213 S’00 – 22 – Building an inter (cont) X Y Z work 2 (ECE) adapter adapter adapter A B C (router) work 1 (SCS) adapter adapter adapter Next we physically connect one of the puters, called a router (in this case puter C), to each of the works. adapter CS 213 S’00 – 23 – Building an inter (cont) X Y Z work 2 (ECE) adapter adapter adapter A B C (router) work 1 (SCS) adapter adapter adapter adapter Finally, we run a software implementation of the Inter Protocol (IP) on each host and router. IP provides a global name space for the hosts, routing messages between work1 and work 2 if necessary. IP addresses: CS 213 S’00 – 24 – Building an inter (cont) inter At this point we have an
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