Embedded Systems November 2000 Vol13_12

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FIGURE 5 Intel's IXP1200 StrongARM Core @ 200MHz little luck. Vector-processing super- computers are used for special pur- pose applications like weather simula- tion, but programmers have not been successful in using them f01ยท general purpose applications. Is there any reason to think net- work processors will fare better? Yes, there is. Network processors are not trying to speed up general purpose processing. Network processing has certain characteristics that are very different from general purpose pro- cessing. Network processing involves less code but more data than general purpose processing. There is less interdependency between the data. Consider a router again . If a router receives n packets, for a small number n, it can proces those packets inde- pendently. Another way of saying this is that processing these packets does- n 't change the router's state. The exception to this would be configura- tion packets, or routing protocol packets. However, even these interde- pendencies are rather loose. If a router receives a packet that indicates it should update its routing tables, there is no reason it can 't finish pro- cessing a few more packets before it does the update. lnterpacket dependencies On the other hand, for the web switch there are substantial interpacket dependencies. A large class of packets must be processed in the order they are received. The web switch must maintain the semantics of a TCP con- nection, which means it must buffer packets it has received until it has received enough to parse out the URL. When forwarding the request to a web server, the web switch must save packets that it has sent but have not yet been acknowledged, in case they need to be resent. Despite these inter-

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