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QOS question ref Voice Signaling Traffic

Hi all,

In going through Wendell Odom's study guide for the QOS exam he mentions the following tidbit in reference to a "Classification and Marking Best Practices Table" in the 10th chapter:

"Notice that the voice and video signaling traffic is listed with a DSCP value of AF31/CS3. As of this writing, Cisco IP Phones mark this traffic as AF31 by default. Within Cisco, a migration is underway to change the marking from AF31 to CS3, leaving AF3 class available for mission critical applications."

My question is: How far along is this "migration"? More to the point do newer models of IP phones mark voice signalling traffic with CS3 (ie: DSCP 24) or is this dependent of the firmware (ie: load files) available for different models of IP phones? Does anyone know exactly what models / when / if the marking change has occured yet? If the change has already been implemented at some level does this not imply the access layer switches should then use the default cos-dscp mapping of COS 3 = DSCP 24? (As opposed to the recommended change of COS 3 = DSCP 26 done by AutoQos for example?)

Thanks in advance for any assistance.

Peter

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Accepted Solutions
Hall of Fame Super Silver

Re: QOS question ref Voice Signaling Traffic

As of CCM 4.0 Cisco has adopted the new IEEE standard of CS3 for voip signaling traffic. Some phones however such as 7905 still use the AF31. As a best practice match both cs3 and af31 in the signaling class, such as:

class-map match-any signal

match ip dscp af31

match ip dscp cs3

HTH, please rate all posts!

Chris

3 REPLIES
Hall of Fame Super Silver

Re: QOS question ref Voice Signaling Traffic

As of CCM 4.0 Cisco has adopted the new IEEE standard of CS3 for voip signaling traffic. Some phones however such as 7905 still use the AF31. As a best practice match both cs3 and af31 in the signaling class, such as:

class-map match-any signal

match ip dscp af31

match ip dscp cs3

HTH, please rate all posts!

Chris

Community Member

Re: QOS question ref Voice Signaling Traffic

Hi Chris,

Thanks for the response and I follow what you're saying about using the class-map statement.

What I don't see is that if Cisco has now adopted the CS3 marking for voice signaling traffic why does AutoQos still change the CoS map such that the CoS 3 marking from IP phone signaling traffic gets remapped to AF31 on a 2950 switch for example? Surely this would now be considered obsolete since CCM 4.0 has been out since at least 2004.

Through out the QOS study guide for exam 642-642 the author still seems to advocate making this change on the access-layer switches either with Auto-QoS or manually.

If most newer IP phones use CS3 I would think they would no longer recommend this change?

Am I missing something? TIA

Bronze

Re: QOS question ref Voice Signaling Traffic

We're running CCM 4.1(3) with 7940s and having the same problem.

What IOS versions are you running on the switch? We have 3560s with 12.2(25) SEB2. I'm wondering if an IOS upgrade would cause AutoQoS to start marking the traffic as CS3 rather than AF31.

I can see how the book would be behind since it was published in 2004, but the latest IOS should certainly be using CS3 I would think.

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