The

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

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

telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...

s in Public Switched Telephone NetworksITU-T Q-Series Recommendations
/ref> as part of the Initial Address Message (IAM). When a

telephone A telephone, colloquially referred to as a phone, is a telecommunications device that enables two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most ...

call is set up from one subscriber to another, many

telephone exchange A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

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

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...

will signal call-related information like called or

calling party The calling party (in some contexts called the "A-Number") is a person who (or device that) initiates a telephone call. The person who, or device that, receives a telephone call is the called party (or callee or B-party). In some countries, it i ...

number to the next

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.

References

Integrated Services Digital Network Signaling System 7 {{telephony-stub