Circuit identification code
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The ISDN Services User Part (ISUP) Circuit Identification Code (CIC) in the Initial Address Message (IAM) consists of a range of 0 to 65,535. On the signalling path the CIC provides information about where the voice part of the call is carried - on which trunk and in which timeslot.
The Bearer Independent Call Control (BICC) Call Instance Code (CIC) in the IAM consists of a range of 0 to 4,294,967,295.
There can be multiple trunk groups to a given point code using a combination of ISUP and BICC signaling. This means, for example, that CIC 100 on an ISUP trunk group can be replicated using CIC 100 on a BICC trunk group to the same point code. The far end switch distinguishes the difference by referencing the Service Indicator (SI). ISUP uses SI=05 and BICC uses SI=13 in North America.
