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

all eligible sources can also get this high allocation. To do this, we add a vari-
able MaxAllocP revious which stores the maximum allocation given in the previous
interval, and another variable MaxAllocCurrent which accumulates the maximum
allocation given during the current switchaveraging interval. The step 9 of the basic
algorithm is replaced by the ow chart shown in gure C.2 (see appendix C).
Basically, for z > 1 + , where is a small fraction, we use the basic ER-
ICA algorithm and allocate the source Max (FairShare, VCShare). But, for z
1+ , we attempt to make all the rate allocations equal. We calculate the ER as
Max (FairShare, VCShare, MaxAllocPrevious).
The key point isthattheV CShare is only used to achieve e ciency. The fairness
can be achieved only by giving the contending sources equal rates. Our solution
attempts to give the sources equal allocations during underload and then divide the
(equal) CCRs by the same z during the subsequent overload to bring them to their
max-min fair shares. The system is considered to be in a state of overload when
its load factor, z, is greater than 1+ . The aim of introducing the quantity is
to force the allocation of equal rates when the overload is uctuating around unity,
thus avoiding unnecessary rate oscillations. The next subsection examines one further
modi cation to the ERICA algorithm.
6.3 Fairshare First to Avoid Transient Overloads
The inter-RM cell time determines how frequently a source receives feedback. It is
also a factor in determining the transient response time when load conditions change.
With the basic ERICA scheme, it is possible that a source which receives feedback
rst can keep getting rate increase indications, purely because it sends more RM cells
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