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

hence, introduces a new parameter, T 0, in place of the target utilization parameter
of ERICA.
6.19 The ERICA+ Scheme
As previously mentioned, the ERICA+ scheme is a modi cation of the ERICA
scheme. In addition to the suggested scheduling method between VBR and ABR
classes, the following are the changes to ERICA.
1. The link utilization is no longer targeted at a constant Target Utilization as
in ERICA. Instead, the total ABR capacity is measured given the link capac-
ity and the VBR bandwidth used in that interval: Total ABR Capacity +
V BR Capacity = Link Capacity
2. The target ABR capacity is a fraction of the total ABR capacity
T arget ABR Capacity f(Tq) T otal ABR Capacity
This function must satisfy the following constraints:
1. It must have avalue greater than or equal to 1whenthe queueing delay, Tq is
0 (zero queues). This allows the queues to increase and Tq can go up to T 0,
the threshold value. A simple choice is to keep the value equal to one. The
queue increases due to the slight errors in measurement. Another alternative is
to have a linear function, with a small slope. Note that, we should not use an
aggressive increase function. Since queueing delay is a highly variant quantity,
a small variation in delay values may cause large changes in rate allocations,
and hence lead to instability.
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