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

The key technique in the scheme is the following. On the lines of the MIT
scheme, the scheme assumes that the source demands a certain rate, and the switch
tries to satisfy that demand. In the scheme, VCi \requests" bandwidth equal to
min(ERi�CCRi). We can consider this as the \demand" of VCi. The same quantity
can also be considered as the bandwidth \usage" of the VC. The scheme computes a
\maximum bandwidth" value Amax depending upon the VC's current state. Amax is
the fairshare which is given to the source as feedback. Next, we describe the states
of the VCs and show how they are used to compute the bandwidth allocations.
Each VCi can be in one of the following two states:
1. Bottlenecked: the switch cannot allocate the requested bandwidth to VCi on
the outgoing link, Amax < min(ERi�CCRi). The set of bottlenecked connec-
tions is B. Intuitively, the bottlenecked connections are those that can use a
higher rate allocation at the switch.
2. Satis ed: the switch can satisfy the request, Amax
min(ERi�CCRi). The
set of bottlenecked connections is S. Intuitively, the bottlenecked connections
are those which cannot use even the current maximum bandwidth allocation
Amax. In some sense, they are currently \saturated."
Typically, a given VCi will be in di erent states (bottlenecked and satis ed) at
di erent switches. Observe that connections can move from one state to another
depending upon their demand and the available bandwidth. Free bandwidth is de-
ned as the amount of bandwidth available as a result of the satis ed connections
not claiming their equal share, Beq. The computation of the maximum bandwidth
allocation for a connection is done as follows.
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