Autoqos and Call Manager Version

[bjfrick]

Concerning the Cat 3550 Software Configuration Guide, starting with 12.1(20)EA2, the Configuration Guidelines for auto-QoS state that connected devices must use Cisco Call Manager Version 4 or later. Does anyone why the CM version would make a difference?

[jasyoung]

The CallManager version makes a difference for QoS, in that CallManager began defaulting to DSCP CS3 (exactly equivalent to precedence 3) for signaling traffic some time ago. The previous default was DSCP AF31. Media traffic remains unchanged at DSCP EF. I am uncertain what exact version the changes took place in, but all versions of CallManager 4.x I believe are using CS3.

[bjfrick]

The configuration guide shows auto-QoS generating DSCP 46 (EF) for voip data traffic and DSCP 24,26 (CS3,AF31) for voip control traffic. Ports that have an ip phone connected to them are trusting the label received from the phone. So if the packets are leaving the switch with the proper QoS label then auto-QoS seems to have done its job. Does the CallManager interfere with this?

[jasyoung]

No, that should all work fine. I've searched for a few minutes and I can't find an auto QoS document that mentions restrictions based on the version of CallManager. If you'll post a link here to the document you're questioning, or email it to me (click on my userid for my profile and address) I'll take a look.

[bjfrick]

Here's the link: http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12120ea2/3550scg/swqos.htm#wp1185337

Thank you very much for your help.