ISDN signaling is used primarily on trunks connecting end-user private branch exchange (PBX) systems to a central office.
It is a packet-switched communication network that allows call control and transaction messages from the voice and data networks to be transferred on communications paths that are separate from the voice and data connections.
CCS messages provide for transaction-based services and for call control signaling between network nodes.
The architecture for a CCS network is generally based on the geographical location of signaling points, the number and sizes of signaling points, the expected traffic load, and the services to be provided by the network.
It provides explicit references to ANSI and ATIS Standards and ITU-T Recommendations.