The scope of this ITU-T Recommendation includes preparation of inter-networking signaling requirements to be used for development of a unique and common Network-to-Network Interface (NNI) protocol. With inputs from ITU-T Recommendations Q.1701 [1], Q.1711 [2] and Q.1721 [3], this ITU-T Recommendation provides signalling and protocol requirements, that are not of information flow name. Specifically, this ITU-T Recommendation includes the following subjects:Description of the signalling layers in accordance with the functional groupings for Call and Bearer Control (CBC), Mobility Management (MM), Packet Services Control (PSC), and VHE Service Control (VSC);State Models for various Functional Entities;NNI instances for Global Roaming and their Reference Points;Signalling Requirements for NNI Protocol(s);Choice of NNI Protocols.