What is CIC (Circuit Identification Code)?

The ISDN Services User Part (ISUP) Circuit Identification Code (CIC) is utilized to establish telephone calls in Public Switched Telephone Networks, as part of the Initial Address Message (IAM).
At the point when a telephone call is established from one subscriber to another, many telephone exchanges will be involved, across international boundaries. To permit a call to be established correctly, a switch will signal call-related data in the network using ISUP messages, where ISUP is supported. The CIC gives data about where the voice part of the call is conveyed, in which time slot.