You may have another problem that I can't analyze from the information given.
First check that the call is switching over in 'show call active voice brief'. You should see the codec as t38. You can also use 'show voice call summary'. If so, check for line slips 'show controllers t1' and packet loss in show call active voice brief. You would need to check the entire call flow, because so far you've only informed of GK--CME--Fax machine. No idea what is to the left of the GK.
SIP traces provide key information in troubleshooting SIP Trunks, SIP
endpoints and other SIP related issues. Even though these traces are in
clear text, these texts can be gibberish unless you understand fully
what they mean. This document attempts to br...
Please find the attached HTML document, download and open it on your PC.
This provides an easy to use form where you simply answer a few
questions and it will render the proper jabber-config.xml file for you
to copy/paste. There is built in logic to verif...
[toc:faq]CUCM Database Replication is an area in which Cisco customers
and partners have asked for more in-depth training in being able to
properly assess a replication problem and potentially resolve an issue
without involving TAC. This document discusse...