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

6.16 ERICA+: Maintain a \Pocket" of Queues
The ABR capacityvaries dynamically, due to the presence of higher priorityclasses
(CBR and VBR). Hence, if the higher priority classes are absent for a short interval
(whichmay be smaller than the feedback delay), the remaining capacity is not utilized.
In such situations, it is useful to have a \pocket" full of ABR cells which use the
available capacity while the RM cells are taking the \good news" to the sources and
asking them to increase their rates.
One way toachieve this e ect is to control the queues to a \target queue length."
In the steady state, the link is 100% utilized, and the queue length is equal to the
target queue length, which is the \pocket" of queues we desire. If the queue length
falls below this value, the sources are encouraged to increase their rate and vice versa.
In other words:
Target rate = function (queue length, target queue length, link rate, VBR rate)
6.17 ERICA+: Scalability to Various Link Speeds
The above function is not scalable to various link speeds because the queue length
measured in cells translates to di erent drain times for di erent transmission speeds.
For example, a queue length of 5 at a T1 link may be considered large while a queue
length of 50 at an OC-3 link may be considered small. This point is signi cant due
to the varying nature of ABR capacity, especially in the presence of VBR sources.
To achieve scalability, we need to measure all queue lengths in units of time rather
than cells. However, the queue is the only directly measurable quantity at the switch.
The queueing delay is then estimated using the measured ABR capacity value. The
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