Telepresence Having One-way audio with PSTN Call

Issue description:

TP MX800 ->SIP ->CUCM ->MGCP ->GW ->PRI.

When off-net calls from PSTN, such as cell phone, to TP’s global line number, sometimes both sides  or one side could not hear each other.

But internal callings have not issues.

This issue is happening on some of our TPs. I captured screenshots on TP when calls from on-net and off-net.

Internal call

External call

Find out that CUCM was invoking a MTP resource to fix a DTMT mismatch between MGCP and SIP legs. Took SDL traces from RTMT to analyze the issue from CUCM perspective.

MTP resource was taken from Default List since MRGL_TP did not have a MTP in the MRG’s

Solution:

Grouped MTP_3 and MTP_4 into a dedicated MRG and then assign it to the MRGL of the MX800. This will force CUCM to allocate local MTP’s into these type of call preventing MTP’s of Default List from begin inserted.