ISUP Overview

ISDN User Part (ISUP) provides signaling support for all voice and non-voice services identified as part of ISDN. ISUP includes all of the flexibility found in the message-oriented signaling of ISDN’s Q.931 message format. It also extends beyond simple call establishment and disestablishment to include network management.

Then ISUP is part of the SS7 which is used to set up telephone calls in Public Switched Telephone Networks. It is specified by the ITU-T as part of the Q.76x series.

ISUP Message Format

-       ISUP information is carried in the Service Information Field (SIF) of an MSU.

-       SIF contains the routing label followed by a 12-bit Circuit Identification Code (CIC).

-       CIC indicated the trunk circuit reserved by the originating switch to carry the call

-       CIC is followed by the message type field

o   IAM, SAM, ACM, ANM, CPG, REL, RLC