The ISDN Services User Part (ISUP) Circuit Identification Code (CIC) is part of the Signaling System #7 which is used to set up telephone call

Telephone call

A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

s in Public Switched Telephone Networks. as part of the Initial Address Message (IAM).

When a telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 call is set up from one subscriber to another, many telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

s will be involved, possibly across international boundaries. To allow a call to be set up correctly, where ISUP is supported, a switch

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

 will signal call-related information like called

Called party

The called party is a person who answers a telephone call. The person who initiates a telephone call is the calling party....

 or calling party

Calling party

The calling party is a person who initiates a telephone call over the public switched telephone network, usually by dialing a telephone number....

 number to the next switch

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

in the network using ISUP messages. The CIC provides information about where the voice part of the call is carried - on which trunk and in which timeslot.