What is ISUP?

ISUP, or ISDN User Part, is a signaling protocol used in telecommunications networks, particularly within the SS7 (Signaling System No. 7) protocol suite. It is used to set up, manage, and release telephone calls over digital circuits. ISUP carries the signaling information needed to establish connections, exchange call-related information (like caller ID), and manage call teardown. It's a critical component for enabling voice and data communication across the Public Switched Telephone Network (PSTN) and is being replaced by newer protocols like SIP in modern networks.