QOS congestion

[donaghq_2]

A defined QOS policy comes in to effect when there is congestion on the interface.

So what happens to voice reserved bandwidth when there is congestion on the interface but there is no voice traffic?! Is that chunk useable to other traffic?

Thanks

DQ

[Peter Paluch]

Hello,

We had recently a very good discussion about this with Adam Styles, Joseph Doherty and Jon Marshall, and I suggest you read it first. I believe it will answer most of your questions.

https://supportforums.cisco.com/message/3423271#3423271

Best regards,

Peter

[Marwan ALshawi]

this is very nice discussion Peter and good findings from you as well

by the way i had a document posted in CSC before already addressed the concept of policing the LLQ at all times using policing command under the LLQ class

example:

a comany run VOIP traffic over this WAN link with the following marking:

VOIP RTP DSCP EF

VOIP Signaling CS3

VOIP RTP traffic must be serviced first in the case of interface congestion and guaranteed and limited at all times to 30 % of the WAN interface bandwidth

https://supportforums.cisco.com/docs/DOC-8373

HTH

[donaghq_2]

Thanks for all your replies.

Peter - I had a read of the post you recommended as well as the tests you completed. Thanks.

You have proved that the priority queue can use the rest of the interface bandwidth providing there is no congestion and policing is not in force.

What about the reverse of this situation;

1. The priority queue has a chunk of data reserved for voice traffic
2. There is congestion on the interface.
3. There is no voice traffic

Can the rest of the traffic use the priority queue?

Leo says this is the case, I was wondering if you agree?

DQ

[lgijssel]

Hi DQ,

Yes, this is indeed the case. The guaranteed bandwidth for voice (priority queue) is not held in reserve when there is no matching traffic. However, when congestion occurs and a matching voip packet arrives, it is forwarded via the priority queue and some other traffic is dropped from the default queue.

When you have congestion, some buffers are full and dropping traffic but while the priority queue has its own dedicated buffer space, there is always room to buffer a voip packet as long as this queue is not also congested.

reagrds,

Leo