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

and
Figure 6.6: The queue control function in ERICA+
f(Tq) =
b Q0
(b ; 1) q + Q0
for 0 q Q0
Note that f(Tq) is a number between 1 and 0 in the range Q0 to in nity and
between b and 1 in the range 0 to Q0. Both curves intersect at Q0, where the value
is 1. These are simple rectangular hyperbolas which assume a value 1 at Q0. This
function is lower bounded by the queue drain limit factor (QDLF):
f(Tq) =Max(QDLF�
6.20 E ect of Variation on ERICA+
a Q0
) forq > Q0
(a ; 1) q + Q0
ERICA+ calculates the target ABR capacity, which is the product of f(Tq) and
the ABR capacity. Both these quantities are variant quantities (random variables),
and the product of two random variables (say, A and B) results in a random variable
which has more variance than either A or B. Feedback becomes less reliable as the
variance increases.
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