voip best practice for QoS

[gavin han]

what's best practice for QoS for voip? what's best practice for queuing and scheduling? do have to configure queuing and scheduling in order to support voip?

[Joseph W. Doherty]

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Posting

Best practice would be to insure your VoIP traffic isn't impacted by other traffic.  Generally,this means insuring the VoIP bearer traffic is transmitted before any other traffic and also to insure VoIP control traffic isn't subject to loss or extreme delay.

Do you have to configure queuing and scheduling so support VoIP?  No, as long as other traffic isn't adverse to the network service needs of VoIP.

[gavin han]

Thanks.

bandwidth is shared and sometimes it gets over utilized. I am going to put priority queue for voice and reserve bandwidth for "dscp ef" and voice signaling. do i still have to do queuing and scheduling in this case?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Using a PQ and/or reserving bandwidth is supported by queues and scheduling how those queues are processed.  Yes, you need to do queues and scheduling to support VoIP QoS.

VoIP bearer is what should be marked DSCP EF.  For that you'll want to use PQ or LLQ.

VoIP control is marked with a DSCP AF4 something or AF3 something (recall [?] RFC and Cisco have different recommendations).  In any case, that traffic would use reserved (or guaranteed) bandwidth.

[gavin han]

Thanks. can you provide sample config for queuing and scheduling for voip?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

A specific sample depends on the platform, but in general, CBWFQ config might look similar to:

class-map match-any VoIP_bearer

match ip dscp EF

class-map match-any VoIP_signaling

match ip dscp CS3

policy-map Sample

class VoIP_bearer

priority percent 33

class VoIP_signaling

bandwidth percent 10