The Integrated Services Digital Network User Part (ISUP) is used for establishment of wired connections between exchanges. It includes messages associated with the connection and disconnection of calls. ISUP is the protocol used to support the signaling necessary to provide voice and non-voice services in telephone communications. It is an extension of SS7, used as the interface protocol for voice and data within, and for ingression or egression to/from the Public Switched Telephone Network (PSTN.)