Media Gateway Controller (MGC)
The internal composition of a PSTN gateway is comprised of at least two components: one component that deals with call signaling on the VoIP network and one component that deals with bearer control on the PSTN side of the gateway.
If the gateway is decomposed into two parts, separating the call control function from the bearer control function, then the part that controls the call control is referred to as a "Media Gateway Controller". This is also sometimes referred to as a "softswitch".
The portion of the decomposed gateway that deals with the bearer connections to the PSTN is referred to as a "Media Gateway".
The MGC function is also referred to as a "Call Agent" in the MGCP specifications.