specifying an appropriate value for the CIR. The strict priority scheme can be used for
low-latency traffic such as Voice over IP and protocol data such as spanning tree
BPDU’s or GVRP PDU’s.
Weighted bandwidth queues are useful to assign a guaranteed bandwidth to each of the
queues. The bandwidth can of course only be guaranteed if concurrent strict priority
queues are appropriately rate-limited.
Usually the queue with the lowest number also has the lowest ranking order, but the
ranking order of the strict priority queues can be redefined.
Important! It is recommended not to change the mode and ranking of the queue
which is used by protocol packets like spanning tree BPDU’s and GVRP PDU’s
(queue 3 or queue 4, respectively; cf. “Traffic class to queue assignment” (p. 8-90)
).
Weight
A weight can be assigned to each port’s egress queue in order to define the ranking of
the queue.
The weight of a strict priority queue has a significance compared to the weight of
other strict priority queues only.
The weight of a weighted bandwidth queue has a significance compared to the weight
of other weighted bandwidth queues only.
The weights of the weighted bandwidth queues are normalized to 100%, whereas the
normalized weights of the strict priority queues indicate just ordering.
Example
The following table shows an example of a scheduler table:
Queue Queue scheduling method Priority/
Weight
4 Strict priority 13
3 Strict priority 12
2 Weighted bandwidth 60
1 Weighted bandwidth 30
The strict priority queues are served before the weighted bandwidth queues. The strict
priority queue with the highest weight is served first, queue 4 in this example.
In this example, the queue 1 will be served 30/(30+60) of the time and queue 2 will be
served 60/(30+60) of the time which is left over from the strict priority queues. In case
frames get queued into strict priority queues, then the queue 4 gets priority over frames
of queue 3.
Traffic provisioning
Classification, queueing, and scheduling
....................................................................................................................................................................................................................................
8-92
Alcatel-Lucent - Proprietary
See notice on first page
365-312-807R7.2
Issue 4, May 2007
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