Alcatel-Lucent 1643 AMS Applications And Planning Manual page 238

Ethernet Overview
Queue scheduling method
Strict priority
Weighted
bandwidth
Each of the two modes has his well-known advantages and drawbacks. Strict priority
queues will always be served before weighted bandwidth queues. So with strict
priority, starvation of the lower priority queues cannot be excluded. Starvation should
be avoided by assuring that upstream policing is configured such that the queue is only
allowed to occupy some fraction of the output link's capacity. This can be done by
setting the strict policing rate control mode for the flows that map into this queue, and
specifying an appropriate value for the CIR. The strict priority scheme can be used for
low-latency traffic such as Voice over IP and internal 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.
(p.
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.
....................................................................................................................................................................................................................................
11-62
The packets in strict priority queues are forwarded strictly according to the queue
ranking. The queue with the highest ranking will be served first. A queue with a
certain ranking will only be served when the queues with a higher ranking are
empty.
The strict priority queues are always served before the weighted bandwidth
queues.
The weights of the weighted bandwidth queues will be summed up; each queue
gets a portion relative to its weight divided by this summed weight, the so-called
normalized weight. The packets in the weighted bandwidth queues are handled in
a Round-Robin order according to their normalized weight.
11-61)).
Alcatel-Lucent - Proprietary
"Traffic class to queue assignment"
See notice on first page
Classification, queueing and scheduling
365-312-801R7.2
Issue 3, May 2007