Previous update was done to support this community to understand MFC / R2 signalling. I have seen several threads regarding Line and Register based sinalling systems based on R1 / R2, DC10, AC9, etc..
For background with these analog signalling feel free to raise your questions.
Since CCITT No 7 (Red, Blue and White books) the Network signalling is now advanced to cater for PAN Network services as opposed to the traditional POT Services.