¿Can CUCM be used to force Softphones to zero the DSCP field?

Answered Question
Mar 9th, 2010

We want to assign flows from Softphones to the "best effort" category in our QoS Model, but we would like to avoid working at LAN Switch level with the "trust" commands.

Then the question is: ¿is there any way to ask CUCM´s administrator to assign Softphones to a group in which the DSCP field of RTP packets are set to 0?

Any hints/ideas will be greatly appreciated.

Best regards, Rogelio

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Correct Answer by Aaron Harrison about 6 years 9 months ago

Hi

I'm not aware of a way to do this - you can adjust the Enterprise Parameters to change what CUMC tells the end points to mark on the packets, but only at a system-wide level.

If you really want to 0 the DSCP out, then you could consider:

1) Using the trust-cisco-phone style switch configs with extend cos 0 to prevent PCs marking

2) On your WAN router remark any voice traffic from the data VLAN to 0, whilst leaving voice traffic from the voice VLAN at EF.

Perhaps if you can tell us why you want to do this we could make more suggestions - doing this at the switch level isn't that complicated.

Regards

Aaron

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Correct Answer
Aaron Harrison Tue, 03/09/2010 - 09:19

Hi

I'm not aware of a way to do this - you can adjust the Enterprise Parameters to change what CUMC tells the end points to mark on the packets, but only at a system-wide level.

If you really want to 0 the DSCP out, then you could consider:

1) Using the trust-cisco-phone style switch configs with extend cos 0 to prevent PCs marking

2) On your WAN router remark any voice traffic from the data VLAN to 0, whilst leaving voice traffic from the voice VLAN at EF.

Perhaps if you can tell us why you want to do this we could make more suggestions - doing this at the switch level isn't that complicated.

Regards

Aaron

Please rate helpful posts..

rogelioalvez Tue, 03/09/2010 - 09:40

I currently am doing CBMarking on my edge routers to "detect" and zero these packets´ DSCP, but it does not scale well since VLANs are created/deleted quite frequently (actually, the LAN admin does not always tell me as soon as he executes a change).

The reason why we want this is basically Call Admission Control. People travel a lot between offices and start their IP Communicators on locations that could belong to other CUCM cluster. When this happens, the user´s CUCM does not know whether a user is (or is not) in its real site, so CAC is not applied properly.

I read a bit about Device Mobility, but as far as I understood, it works WITHIN a cluster. In my case, the company has three CUCM clusters, and mobile users might want to start IP Communicator across any of these clusters.

Thank you very much again for any hints you may give me.

Regards, Rogelio

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