Call control protocol for digital cellular radio interface

The layer-three call control (CC) signaling protocol structure is discussed. CC is based on the Q.931 protocol in order to facilitate expansion of the services and interconnection with the ISDN. In Japan, a simple subset of Q.931 messages is provided in the first step in order to spread the digital mobile service nationwide in a short time. In the second step, CC will be expanded to offer all the services of Q.931, although, to ensure efficient signal transmission, they have been modified from Q.931 and Q.932 to reduce the message length and the number of messages in each procedure. As CC becomes more widely used, various basic and supplementary services can be provided