Telephone User Part

Telephone User Part (TUP) provides conventional

PSTN The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

telephony services across the

Signalling System No. 7 Signalling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also perfo ...

(SS7) network. TUP was the first layer 4 protocol defined by the standards bodies and as such did not provision for

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

services. It has now largely been replaced by ISUP. However, it can still be found in operational use in some parts of the world (e.g., China). TUP is defined in

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Comm ...

Recommendations Q.721-725. These define the international telephone call control signalling functions for use over SS7. Various national variants of TUP have evolved, some of which provide varying degrees of support for

. E.g. French SSUTR2 and Chinese TUP (Specification GF001-9001). Signaling System 7 Integrated Services Digital Network {{telephony-stub