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

ER in both the forward and backward directions. It assumes that the destination
resets the ER eld to the peak cell rate (PCR), which isnotmandated by the tra c
management standard. Since it derives from the properties of the MIT scheme, it is
fair. The setting of feedback in both the forward and backward directions improves
the response of the scheme compared to the MIT scheme. Another interesting aspect
is that due to the bidirectional ER setting, and the resetting at the destination,
the minimum of ER elds in the forward and backward directions gives the current
bottleneck rate for that VC.
4.12.2 Discussion
Though given the above interesting aspects, the scheme has several drawbacks:
It retains the O(N) complexity of the MIT scheme. Further, doing the ER
calculation at the receipt of both the forward and backward RM cells increases
the computation burden on the switch.
The scheme does no load measurement, and as a result may not work if the
sources are bottlenecked at rates below their allocations.
The scheme does not measure the number of active VCs, and uses the (static)
total number of VCs for the computation.
The scheme is incompatible with the ATM Forum's Tra c Management 4.0
speci cation since it requires the ER to be reset by the destination.
It is not clear how the scheme accounts for variable capacity, especially the
handling of queues which build up during transient phases.
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