Calls through the MGCP gateway to the PSTN are disconnected if the remote end phone does not answer the call within 20-25 seconds. The MGCP gateway sends an unexpected DLCX and tears down a call midstream. The debug mgcp all command shows disconnect cause

[TCC_2]

Core Issue

If the calls are answered within 20-25 seconds of ringout, the calls remain connected and have no issues. However, if not answered, the calls drop.

In the MGCP Delete Connection (DLCX) message, the reason code is 902, a loss of lower-layer connectivity.

The MGCP gateway gets a disconnect event from the lower (CCAPI) layer and sends a DLCX.

Resolution

In order to resolve the issue, add these two commands to the MGCP gateway:

mgcp rtp unreachable timeout 1000 action notify
no mgcp timer receive-rtcp

Ideally, this resolves the mid-call drop issue.