ITU-T Q.87.1

This Recommendation describes the Stage 2 of the User-to-User Signalling supplementary service supported by an ISDN. The Stage 2 descriptions are comprised of the switching functions and signalling information flows. The User-to-User Signalling supplementary service allows an ISDN user to send/receive a limited amount of information to/from another ISDN user over the signalling channel in association with a call to the other ISDN user. NOTE - These procedures are applicable to User-to-User Information Transfer in association with a circuit-switched telecommunication service only. Procedures to permit User-to-User Information transfer in association with other types of calls (e. g. packet bearer services) need to be investigated.