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

The use of the utilization factor introduces higher degree of variation in load,
and the possibility of sharp queue spikes. This necessitates complex variance
reduction and queue control techniques within the algorithm, and introduces
several extra parameters. The scheme may also require the sources to negotiate
a lower value of the \Rate Increase Factor (RIF)" parameter to moderate the
network-directed rate increases.
The queue thresholding procedures may require a new set of parameter recom-
mendations for Wide Area Networks. It is not clear whether the scheme will
work in WANs without complex parameter changes.
4.9 UCSC Scheme
This scheme was proposed by researchers Kalampoukas and Varma at the Univer-
sity of California, Santa Cruz (UCSC), and K.K. Ramakrishnan of AT&T Research
[58].
4.9.1 Key Techniques
The scheme cleverly approximates the MIT scheme with O(1) bookkeeping, and
hence brings the computational complexity from O(N) to O(1). Intuitively, the
scheme spreads the MIT O(N) iteration over successive RM cells. As a result, the
convergence time and bu er requirements are traded o with computational com-
plexity. The space requirements compared to the MIT scheme remain O(N) since the
scheme maintains some per-VC state information. In special cases, optimization may
be achieved by using shift operations instead of multiply/divide operations.
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