Circuit identification code (CIC)

In the Quasi-associated Signaling Mode the signaling messages
belonging to one call may take different paths than speech. The
speech goes directly from node A to B. The signals go via node C
which acts as a transit node. Hence node C is called the Signal
Transfer Point (STP).
The call set-up data sent in a message is not used in the STP node
C. The STP simply reroutes the messages to node B. Therefore, it is
required that the MSU carries some sort of label. The label
indicates not only the source and destination of the MSU, but also
the identity of the speech trunk the message is referring to. This
identity is called the Circuit Identity Code (CIC).

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