The Telephone User Part (TUP) provides the signaling backbone between switching elements for basic call establishment, supervision, and release of circuit switched network connections for telecommunications services. TUP supports analog and digital circuits, and limited call management signaling.

TUP controls the circuits used to carry voice traffic. Also using TUP, the state of circuits can be verified and managed. TUP is good in supporting applications such as switching and voice mail in which calls are routed between endpoints in either fixed or wireless networks.

While Telephone User Part (TUP) is still in use currently, but it is fallen out of favor except in certain parts of the world such as China. TUP is replaced by ISUP which adds support for data, advanced ISDN and Intelligent Network.

The TUP header structure is as follows:

Message Type Code - It basically contains the label, the heading code and one or more signals and/or indications. The service information octet comprises the service indicator and the subservice field. The service indicator is used to associate signalling information with a particular User Part and is only used with message signal units. The information in the subservice field permits a distinction to be made between national and international signalling messages. In national applications when this discrimination is not required possibly for certain national User Parts only, the subservice field can be used independently for different User Parts.

Related Terms: SS7, ASP, BICC, BISUP, ISUP, MTP, SCCP, TCAP, DUP, MAP

Sponsor Source: TUP is defined by the ITU-T Q.723 and ISUP is defined in ITU-T Q.763.

Reference Links:
http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-Q.723: SS7 Telephone User Part
http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-Q.763: SS7 ISDN User Part