Very strange this one.
We have multiple customers running SP Services 12.4-15T12 and we appeared to hit an intermittent bug with a particular customer. This customer has a 2800 series router with 2x E1 links to a PBX using QSIG. The symptoms are that occasionally you get no-way voice across the trunk to the PBX, when the call originates from either direction. I've been running 12.4-24T3 for a few days now and the issue doesn't appear to have occurred again.
Here is the response from TAC:
It can happen on any gateway that is using c5510 DSPs (PVDM2-x where x=
8 or 16 or 32 or 64) using IOS 124-15T10 through 124-15T13 (dsp version
9.4.9 through 9.4.12).
My suggestion would be to keep an eye on it cause the bug does not happen *all* the time, it is a intermittent and random issue where you will start experiencing random one-way or no-way or complete dead air calls. You can open a TAC case at that point and get the DSP firmware from the fix.
So to clarify:
Once the issue is encountered and you want to stay on 124-15T train until 124-15T14 is released on CCO, you will have to:
load 1240-15T13 IOS image PLUS also contact TAC and get the DSP firmware version (which will eventually be bundled in 124-15T14). The bug id you can reference is CSCtf25886.