Configure DSCP of Call Control messages on Cisco SIP Phones (7940 & 7960)

[tsim]

Is it possible for me to configure the DSCP values of SIP call control messages sent from Cisco SIP phones (7940 & 7960 specifically) to AF31, using a configuration file - much like setting the tos_media parameter? Any help will be greatly appreciated!

[James Hawkins]

Hi,

I do not think you can do this but to allow us to check please confirm whether you are using with phones with CallManager or CallManager Express or with a third party IP PABX - e.g. Asterix?

If it is not possible you could always set up you LAN switches (assuming something like Catalyst 3560) to classify and mark the traffic on ingress to the network.

[tsim]

Hi, thanks for your response. No, we're neither using a CallManager or the Express. We're using sipXpbx from SIP Foundry/PingTel. As you said, we're planning on remarking the call control packets on the LAN switches if we can confirm that the call control messages' QoS cannot be modified through configuration files.

Thanks for checking out!

[James Hawkins]

Hi,

For CallManager DSCP values are set using the "Enterprise Parameters" page.

There are DSCP settings for:

Phone-based Services - This parameter specifies the Differentiated Service Code Point (DSCP) IP classification for IP phone services on phones, including any HTTP traffic.

Phone Configuration - This parameter specifies the Differentiated Service Code Point (DSCP) IP classification for any phone configuration, including any TFTP, DNS, or DHCP access that is necessary for phone configuration.

Cisco CallManager to Device Interface - This parameter specifies the Differentiated Service Code Point (DSCP) IP classification for protocol control interfaces that are used in Cisco CallManager-to-device communications.

These are mapped into the CNF files that phones download when booting.

To change the signalling DSCP you would need to change the Cisco CallManager to Device Interface setting which is referenced as within the CNF file.

I do not know whether your product stores CNF filesas flat files for retrieval via TFTP. if so you could try editing them to set the DSCP value.

I would remark the traffic using the switches myself!

[tsim]

Thank you very much, I'll definitely try that!!