Two LLQs in CBWFQ

[evanlau]

If you configure two (or more) LLQs in CBWFQ, e.g. one for voice and one for video, how does a router service these queues? Does it:

1. Behave like PQ with one queue having a larger priority than the other, i.e. if it's servicing the second configured queue and packets come into the first queue, it will abandon the second queue and service the first; or

2. Behave like PQ with both queues having the same priority, i.e. if it's servicing the second configured queue and packets come into the first queue, it will finish servicing the second queue before servicing the first.

In relation to the above, have most people had more success with:

1. Voice and video in the same LLQ;

2. Voice and video in two separate LLQs; or

3. Voice in the LLQ and video in one of the CBWFQs.

I know that Cisco has done some testing with bandwidths above 768kbps with CAC and placing voice and video in the same LLQ, not resulting in significant delays added to the voice traffic. I would like to know others' experiences.

Cheers.

[allan.wells]

Hi Their,

Their is only one priority queue with LLQ

Using the priority command.

Your class that the priority queue uses could match both video and data whatever else you classify.

And that data will be sent/dequeued from the priority queue in the order it arrives in the queue.And will consume the ammount of BW you specified with the priority command if it needs the BW otherwise it will be made available to other classes.

Allan

[evanlau]

I believe in 12.2 (or maybe earlier) comes the introduction of multiple LLQs for CBWFQ, along with other new features such as the ability to configure percentage of bandwidth rather than bandwidth itself, and the aiblity to configure burst sizes for the LLQ (useful for video).

[allan.wells]

Hi Evan,

Thats news to me do you have the link that describes this behaviour.

Its not mentioned below.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/qcfintro.htm#1001082

[evanlau]

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns17/c649/ccmigration_09186a00800d67ed.pdf

Pages 1-19 to 1-20. It mentions that 12.2 allows for the burst size to be configured in the LLQ. At the end of 1-19, it says "More than one LLQ can be provisioned....etc". It doesn't mention 12.2 but the document references that IOS version a lot.

[Erick Bergquist]

There is only 1 priority queue per interface if I recall correctly from DQOS, etc. I asked this same question in DQOS and didn't get a good answer.

Here's why you can do it; haven't came across a situation where I needed to use it this way but could be helpful I guess and shows why the MQC is flexible.

If you have a policy with multiple priority classes, then you can match and do different actions on the traffic per class. Thats it. Since the traffic is all priority it will placed in the same priority queue on interface.