Details: IMT
Signaling System 7 (SS7) signaling is transmitted over a full-duplex, 64 kbit/s digital transmission channel. SS7 uses physical out-of-band signaling, which means that signaling information is transmitted on a different line from the voice/data information. In fact, SS7 can use an entirely separate network for signaling. User traffic flows over inter-machine trunks (IMTs). When you configure SS7, you identify an SS7 gateway to the signaling network that does call management for user traffic on IMTs.
Because modem pools are managed on a slot-by-slot basis, each slot in the PM4 configured for IMTs is an SS7 client and sets up an independent session with the SS7 Gateway. Only 96 modems are supported.