Cisco Router 2921 as MGCP gateway.
Cisco IP phone 6921 & 7911.
If IP phone gets abruptly powered off when it is on call with other PSTN party, the call does not get terminated at router & PSTN party remains on call.
Thus PRI channel still remain consumed at router (PRI gateway).
So what should be configured so that PRI channel does not remain consumed when above scenario occurs.