ntegrated ervices Digital Network ser art ISUP is a layer of the SS7 protocol; ISUP messages are connection-oriented messages used to set up and tear down telephone calls; ISUP defines a handshaking protocol that initiates the phone call, reserves a path for the voice or data between the originating and destination devices, and ultimately releases the call; note that despite the name of this part of the SS7 stack, ISUP messages are not limited to ISDN calls. Performance Technologies' SS7 Tutorial
ISDN User Part (SS7). ISDN User Part is part of the SS7 (Signaling System No.7) protocol layer and used in the setting up, management, and release of trunks that carry voice and data between calling and called parties. ISUP Trunk Signaling is an important Connectivity and Interoperability Services offered by VeriSign.