QOS voice and video

Unanswered Question
Jan 20th, 2009

Can someone clarify how to best setup video and voice queuing? It seems that if voice is in the priorty Q video falls to a CBWFQ queue. But what is the best way to give video preferntial treatment liek voice w/o using a priority queue?

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michael murphy Wed, 01/21/2009 - 08:49

Thanks. What about on the campus side? I've read NOT to put video in a priorty queue with voice due to its varible packet size. Can you commnent? Client is seeing dropped video packets on their campus not WAN. What would be potential culprit?

Brandon Buffin Wed, 01/21/2009 - 08:59

Yes, that is correct. The recommendation is for video to be put into Q3 based on DSCP/CoS values. See page 2-27 of the QoS SRND. Is the video traffic being marked correctly and those marking passed through the network?


michael murphy Wed, 01/21/2009 - 09:23

What is the difference between DSCP AF41 and CS4 for video? I understand the drop precedence based on the DSCP value for AF41 but what is the drop predence for CS4? Why isn't AF42 used instead? thanks-

babatunde_sanda Sat, 02/28/2009 - 05:30

This question requires some reading on your part but just a crash explanation.

The CS values are there for you if you want to use dscp but stick with COS values. If you do a question mark, you will notice that the full COS class are after the DSCP. The DSCP values gives you more control for marking or classifying. 3 bits are used for COS giving a total of 8 (0 - 7). DSCP uses 6 bits a total of 64 (0 - 63). You will see from the question mark that you can even specify the number 0 - 63 instead of using the AF values. This is being too granular though. Always think of the first value as superior AF41 (4 , 1) 4 marks to COS 4 first three bits for cos. 1, second value representing dscp. Next three bits. AF41 and AF42 AF (assured forwarding) knowing 4 = superior and 1 = minor AF41 will be given priority over AF42. 111 / 111/ 11. First three COS, first 6 DSCP last two ECN bits. First six from right the first bit there will always be 0. The makers of DSCP didn't make it too easy for understanding (someone had too much time on there hand)


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