This feature (CSCea78597) implements some enhanced functions based on the original per call trace, including collecting per call trace on calling/called party number, adding MCL setting, capturing long duration calls, collecting call trace on cause value and fixing per call trace on a particular sigPath/Span/cic (or trunkgroup/trunk) combinations.

To implement this feature, there is a new XECfgParm parameter, CallNumberToWriteIntoTracefile that limits the call number to write into a trace file while stopping a long duration call trace.

http://www.cisco.com/en/US/docs/voice_ip_comm/pgw/9/release/note/rn973.html#wp1233148