scope:

This standard defines the stage two of the Three-Party (3PTY) supplementary service for the pan- European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators. Stage two identifies the functional capabilities and the information flows needed to support the service as described in stage one. The stage two description also identifies user operations not directly associated with a call (see CCITT Recommendation I.130 [2]).

This standard is specified according to the methodology specified in CCITT Recommendation Q.65 [3].

In addition this standard does not specify the requirements where the service is provided to the user via a private ISDN. This standard does not specify the requirements for the allocation of defined functional entities within a private ISDN, it does however define which functional entities may be allocated to a private ISDN.

This standard does not specify the additional requirements where the service is provided to the user via a telecommunications network that is not an ISDN.

The 3PTY supplementary service enables a user to establish, participate in and control, a three-way conversation, i.e. a simultaneous communication involving the served user and two remote parties.

The 3PTY supplementary service is applicable to all circuit-switched telecommunication services carrying speech.

This standard is the stage three standard for the ISDN 3PTY supplementary service. The term "stage three" is also defined in CCITT Recommendation I.130 [2]. Where the text indicates the status of a requirement (i.e. as a strict command or prohibition, as authorisation leaving freedom, or as a capability or possibility), this shall be reflected in the text of the relevant stage three standard.

Furthermore, conformance to this standard is met by conforming to the stage three standard with the field of application appropriate to the equipment being implemented. Therefore, no method of testing is provided for this standard.