Q.931
Q.931 is the protocol standardized by the International Telecommunication Union( ITU) for signaling in the D channel of ISDN, which is used for call setup, call termination, and call control.
Q.931 is a component of SS7 signaling, but is also used in network configurations other than ISDN for its signaling. For example, in H.323 networks Remote Access Service( RAS) for registering terminals with the gatekeeper can be handled via Q.931.