DSCP QoS Markings

[drbabbers]

I have a Catalyst LAN with Cisco Jabber softphones and Cisco 7942 IP Phones connected to CUCM 10.5. I have setup Auto QoS in the LAN with the 'auto qos voip cisco-phone' command on all edge ports to phones and 'auto qos voip trust' on all trunks/uplinks. I use a Group Policy Object to mark the DSCP value to 46 for EF.

I can see in a Wireshark capture that packets are successfully being marked with EF, however when the packet come back either in an RTP stream from the Voice Gateway or the SIP signalling to CUCM, I never see the marking for DSCP 46.

Wireshark example with an RTP stream:

15967 125.070773000 JABBER ENDPOINT IP VOICE GATEWAY IP RTP 214 PT=ITU-T G.711 PCMU, SSRC=0x6DC33AE5, Seq=28887, Time=1321215841

Differentiated Services Field: 0xb8 (DSCP 0x2e: Expedited Forwarding; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))

15968 125.086944000 VOICE GATEWAY JABBER ENDPOINT RTP 214 PT=ITU-T G.711 PCMU, SSRC=0x1A5F45FE, Seq=10910, Time=3589300385

Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))

My question is should the return traffic still be marked with EF?

Dean

[drbabbers]

Just to add to this, when I setup an RTP stream between 2 phones, I see the EF markings in both directions, so I think this answers my question.

So this is something unique to CUCM and the Voice Gateway. Ill check the QoS setup on the edge ports connected to CUCM and the VG.

[Terry Cheema · Accepted solution]

The return RTP audio traffic should have the markings, but depending on QoS is configured both ways, correctly.

-Terry

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