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

The OSU scheme was one of the rst explicit rate schemes designed for ABR. It
exposed some of the pitfalls in using window-based control techniques in rate-based
control. The key contributions of the algorithm are:
Choice of congestion indicator (input rate i.e. aggregate demand, instead of
queue length)
Application of the congestion avoidance concept in rate-based control (use of
the target utilization parameter).
Use of the \overload factor" and \equal fairshare" metrics instead of simply the
queue length.
Small number of parameters
Measurement of the number of active sources. In general, the scheme uses
measurement instead of beleiving the declared values of metrics.
O(1) time complexity.
A proof that the fairness algorithm does achieve fairness.
The drawbacks of the scheme are its slow convergence in complex con gurations,
and the fact that it is incompatible with the nal version of the standard (since it
was developed at a time when the standards themselves were not nalized).
Three di erent options that further improve the performance over the basic scheme
are also described. These allow the fairness to be achieved quickly, oscillations to be
minimized, and feedback delay tobe reduced.
The OSU scheme drawbacks were addressed in the ERICA schemes. The ERICA
set of schemes use an optimistic approach to provide good steady state as well as
375