In order to get the trace for ISDN Q.931 messages, please select the option of 'Trace' under Call Manager serviceability.
Under trace,go to the Configuration option and choose the CCM server that you use.Then it will lead to another window that lists all the configured services. Please select the "Cisco callManager" option and go thru the following steps
(a)Enable 'Trace On'
(b)For Trace Filter Settings, set the Debug Trace Level option
to Detailed.
(c)Under cisco callManager Trace fields, enable
Enable PRI Traceand Enable ISDN translation Trace.