Transparent Common Channel Signaling (T-CCS) is broken for the medium complexity codec setting in Cisco IOS Software Releases 12.3(5), 12.3(4)T and in 12.2(13)T, starting with 12.2(13)T8.
Any Cisco IOS Software using Cisco voice Digital Signal Processor (DSP) code base (DSPWare) 4.1.33 or later is affected.
For more information on the Cisco IOS Software builds that may have this issue, refer to Cisco bug ID CSCeb66176.
For more information, refer to these Cisco bug IDs:
For a resolution to this bug, refer to the Bug Toolkit.
For a temporary workaround, use high complexity codec or Serial Tunneling (STUN).