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Bandwidth for High Speed Networks

This was intentional as the csfq approach can be

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Unformatted text preview: ters are typically not on the high-speed backbone links then there is no problem as classi cation at moderate speeds is quite practical. 2.6 Architectural Considerations We have used the term ow without de ning what we mean. This was intentional, as the CSFQ approach can be applied to varying degrees of ow granularity; that is, what constitutes a ow is arbitrary as long as all packets in the ow follow the same path within the core. In this paper, for convenience, a ow is implicitly de ned as a source-destination pair, but one could easily assign fair rates to many other granularities such as source-destination-ports. Moreover, the unit of ow" can vary from island to island as long as the rates are re-estimated when entering a new island. Similarly, we have not been precise about the size of these CSFQ islands. In one extreme, we could take each router as an island and estimate rates at every router; this would allow us to avoid the use of complicated per- ow scheduling and dropping algorithms, but would require per- ow classication. Another possibility is that ISP's could extend their island of CSFQ routers to the very edge of their network, having their edge routers at the points where customer's packets enter the ISP's network. Building on the previous scenario, multiple ISP's could combine their islands so that classi cation and estimation did not have to be performed at ISP-ISP boundaries. The key obstacle here is one of trust between ISPs. Having presented the basic CSFQ algorithm, we now return to discuss a few aspects in more detail. We have used exponential averaging to estimate the arrival rate in Eq. 3. However, instead of using a constant exponential weight we used e,T=K where T is the interpacket arrival time and K is a constant. Our motivation was that e,T=K more closely re ects a uid averaging process which is independent of the packetizing structure. More speci cally, it can be shown that if a constant weight is used, the estimated rate will be sensitive to...
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