Unformatted text preview: the packet length distribution and there are pathological cases where the estimated rate di ers from the real arrival rate by a factor;
this would allow ows to exploit the estimation process and
obtain more than their fair share. In contrast, by using a
parameter of e,T=K , the estimated rate will asymptotically
converge to the real rate, and this allows us to bound the
excess service that can be achieved as in Theorem 1. We
used a similar averaging process in Eq. 5 to estimate the
total arrival rate A.
The choice of K in the above expression e,T=K presents
us with several tradeo s. First, while a smaller K increases
the system responsiveness to rapid rate uctuations, a larger
K better lters the noise and avoids potential system instability. Second, K should be large enough such that the estimated rate, calculated at the edge of the network, remains
reasonably accurate after a packet traverses multiple links.
This is because the delay-jitter changes the packets' interarrival pattern, which may result in an increased discrepancy between the estimated rate received in the packets'
labels and the real rate. To counteract this e ect, as a rule
of thumb, K should be one order of magnitude larger that
the delay-jitter experienced by a ow over a time interval of
the same size, K . Third, K should be no larger than the
average duration of a ow. Based on this constraints, an
appropriate value for K would be between 100 and 500 ms.
A second issue relates to the requirement of CSFQ for a
label to be carried in each packet. One possibility is to use
the Type Of Service byte in the IP header. For example, by
using a oating point representation with four bits for mantissa and four bits for exponent we can represents any rate
between 1 Kbps and 65 Mbps with an accuracy of 6.25.
Another possibility is to de ne an IP option in the case of
IPv4, or a hop-by-hop extension header in the case of IPv6. 3 Simulations
In this section we evaluate our algorithm by simulation. To
provide some context, we compare CSFQ's performance to
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This document was uploaded on 03/04/2014 for the course ENG 531 at Rice.
- Fall '10
- Eugene Ng