The present document specifies the stage three of the Conference call, add-on (CONF) supplementary service for the
pan-European Integrated Services Digital Network (ISDN) as provided by the European public telecommunications
operators by means of the Signalling System No.7 protocol for the ISDN User Part (ISUP). Stage three identifies the
protocol procedures and switching functions needed to support a telecommunication service (see ITU-T
Recommendation I.130 [1]).
The present document does not specify the additional protocol requirements where the service is provided to the user
via a telecommunications network that is not an ISDN.
The present document does not specify the additional protocol requirements for the national signalling interface.
Although the present document applies only to the international interconnection, the specification of functions, formats
and codes of messages and signals, and actions performed at originating and destination local exchanges are retained.
Formats, codes and procedures marked for national use are included for informative purposes for the international
interface specification. If these items so marked are supported within a national network and operators network, then it
is proposed that they shall be supported in this manner.
NOTE: In the case where a national signalling system behaves differently, the international gateway exchange is
to support both the concerned national and international network.
The CONF supplementary service provides a user with the ability to have multi-connection call, i.e. a simultaneous
communication between more than two parties.
The CONF supplementary service is applicable to all telecommunication services carrying speech.