Summary

ISUP provides a rich network interface to call processing at an SSP. The increased bandwidth and protocol standardization allow a greater range of services that are able to interwork both within a network and across network boundaries. ISUP was designed to interface well with ISDN access signaling by providing event mapping and facilitating end-to-end user signaling. The protocol's use of optional message parameters achieves flexibility and extensibility.

ISUP uses a CIC identifier in each message to correlate the signaling with the correct circuit. The CIC is the key to associating signaling with bearer circuits.

ISUP also provides a set of maintenance messages for diagnostics and maintenance of ISUP facilities. These messages allow for blocking, testing, and resetting circuits and inquiring about circuit status.