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 [1].)

This standard specified according to the methodology specified in CCITT Recommendation Q. 65[2].

In addition this standard does not specify the requirement 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 who is involved in at least to calls (one active call and one call on hold) to join the two calls together into a three-way conversation, i.3. a simultaneous communication between the served user an two other parties.

This supplementary service is not applicable to non-voice services.

This standard is applicable to all telecommunication services carrying speech.