Traffic Management for the Available Bit Rate (ABR) Service in ...

ursty or ACR retaining sources. A drawback of this strategy is that in certain con-
gurations, the link may not be fully utilized if the entire tra c is bursty. This is
because all the bursty sources are asked to send at F airShare, which may not be
the optimal value if some sources are bottlenecked elsewhere. This option can also
be enabled and disabled based upon a certain queue threshold.
6.9 Averaging of the Number of Sources
Another technique to overcome the problem of underestimating the number of
active sources is to use exponential averaging to decay the contribution of each VC
to the numberofactive sources count. The main motivation behind this idea is that
if a source is inactive during the current interval, but was recently active, it should
still contribute to the numberofactive sources. This is because this source might be
sending its data in bursts, and just happened to be idle during the current interval.
Flow charts of gures C.4 and C.5 show this technique (see appendix C).
The DecayF actor used in decaying the contribution of each VCisavalue between
zero and one, and is usually selected to be a large fraction, say 0.9. The larger the
value of the DecayF actor, the larger the contribution of the sources active in prior
intervals, and the less sensitive the scheme is to measurement errors. Setting the
DecayF actor to a smaller fraction makes the scheme adapt faster to sources which
become idle, but makes the scheme more sensitive to the averaging interval length.
6.10 Boundary Cases
Two boundary conditions are introduced in the calculations at the end of the
averaging interval. First, the estimated number of active sources should never be less
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