Hi Abdel,
From a QoS-only point of view, the configuration on the Cisco Switch shouldn't be much different from when you connect a Cisco IP Phone. Providing the Avaya phone can mark signalling and voice packets accordingly, it's just a matter of trusting the DSCP/COS values and then applying the corresponding bandwidth reservation commands. You might need to re-configure the standard mapping of COS to DSCP as Cisco's values might not be the same as the ones used by Avaya phones though.
Have a look at the attached document from the Avaya website:
http://www.avaya.com/usa/resource/assets/applicationnotes/Config-autoqos.pdf
Cheers,
Jose
