SS7 is an example of CCS (Common Channel Signalling ) Protocol
- It is not a single protocol
- It is a suite of Protocol
- It is not an access protocol
- It is a net work protocol
- It is point to multipoint
ISUP(ISDN user part) and TUP (Telephone User Part) are in the call control layer
There is MTP (Message transyer layer ) which has three layers:-MTP1 , MTP2 , MTP3
Here in MTP1 (OSI -Physical layer ) has E1,T1
My opinion
So we have E1 , T1 links available in MTP1 layer , is this enough for the PBX . ie If we take the E1 link from MTP1 to the foneBRIDGE , it should work.