ISUP connects, manages, and disconnects all voice and data calls in the PSTN. ISUP sets up and tears down the circuits used to connect PSTN voice and data subscribers. The subscribers include ISDN, analog, and ISDN-to-analog users. ISUP also is used in cellular or mobile networks for trunking connections. ISUP is widely implemented in North America and is preferred over TUP . Internationally, ISUP also is widely adopted, although several national variations exist. ISUP offers increased capabilities and services over TUP. The broadband ISUP (BISUP) signaling protocol for broadband network services is not covered in this book.

ISUP information is transferred in MTP3 messages similar to the other L4 protocols. The ISUP section covers the following topics:

• ISUP Services—Basic and Supplementary

• End-to-end Signaling—Pass-along and SCCP

• Call Setup and Teardown

• ISUP Message Format

• ISUP Call Control Messages

The "SS7 Examples" section later in this chapter provides basic call setup and teardown examples that include ISUP messages.

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