Overview

The ISDN User Part (ISUP) has been used in U.S. networks for many years now as an alternative to the European equivalent, the Telephone User Part (TUP). In early implementations of Signaling System 7 (SS7), TUP was found to be far too limited for the scope of North American networks and was modified to align with the future services of the Integrated Services Digital Network (ISDN) and many other network features still under development. Today, many of those features are under implementation, and the SS7 network is being used more and more. However, much of its potential is still untapped.

ISUP has been a good protocol for circuit-related messages but is already under modification to support new broadband services soon to be offered by major telephone companies. The new broadband services being offered for tomorrow s networks will require a new version of ISUP called broadband ISUP (BISUP).

The ISUP is used to set up and tear down all circuits used for data or voice calls in the Public Switched Telephone Network (PSTN). In addition to its use in the PSTN, ISUP also can be found in wireless networks for establishing trunk connections between switching centers. ISUP is not used widely throughout the world; in fact, the United States was the first to adopt ISUP for use in its networks. The International Telecommunications Union (ITU) is currently developing an international version of ISUP, which will be used in the international plane. Other countries...