Subject: [Diffserv] Alternative congestion avoidance parameterization (diffserv-mib-01)

From: "Alain BURGAIN" <[email-masked]>
Date: Fri, 05 Nov 1999 11:34:18 +0100

Hello,

========================================================================

Proposal of an alternative congestion avoidance parameterization for a
more precise queuing delay control.
========================================================================

In term of service differentiation, at least for some service classes,
the number of packets in a queue has not a clear meaning for the user
(or for the network administrator). What is important is the control
over the queuing delay for each class of service.

To trigger drop decision, the evaluation of the pre-congestion level
should then be performed according to the current (instantaneous or
average) queuing delay. That is to say drop thresholds are (optionally)
configured in microseconds, in the diffServActionTable.
When a variable bit rate subnetwork is used, the implementation is then
able to take into account the exact [average] queuing delay for each
packet (provided that the current rate of the subnetwork connection is
known. Suitable purge actions may also be needed after a sudden decrease
of this service rate).

To keep compatibility with congestion avoidance implementations taking
into account the number of packets in the queue, we can propose two
possibilities :
- The MIB thresholds parameters, expressed in microseconds in the MIB,
are converted by the router into a number of packets, provided that the
service rate of the queue, and the average packet size are known by the
router.
- The new behavior is optional in the MIB : a
“diffServQueueFillingControl” parameter, indicating whether to use
packet number thresholds or queuing delay thresholds can be specified in
the diffServQueueTable entry that is pointed by the diffServActionTable
entry.

Bye
Alain BURGAIN

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