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

The capacity unused by the underloading VCs is divided equally among the over-
loading VCs. Thus, the fair share of the VCs is calculated as follows:
Fair Share =
Capacity ; P Bandwidth of underloading VCs
total number of VCs ; NumberofunderloadingVCs
It is possible that that after this calculation some VCs that were previously un-
derloading with respect to the old fair share can become overloading with respect to
the new fair share. In this case these VCs are re-marked as overloading and the fair
share is recalculated.
Charny [17] has shown that two iterations are su cient for this procedure to
converge. Charny also showed that the MIT scheme achieves max-min optimality in
4k round trips, where k is the number of bottlenecks.
4.5.2 Discussion
The contributions of the MIT scheme were as follows:
Help de ne the framework for explicit rate feedback mechanisms in the ATM
ABR speci cations
Provided a reference iterative algorithm
Max-min fairness is achieved because the underloading VCs see the same ad-
vertised rate
The switch algorithm is essentially a rate calculation algorithm which is not
concerned with the enforcement of the rates. The enforcement of rates may be
carried out either at the edge of the network or at every network switch though
queuing and scheduling policies. This algorithm gives the network designer the
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