22.0873GPPService descriptionStage 1TSUser-to-User Signalling (UUS)
The UUS supplementary service allows the served subscriber to send/receive a limited amount of subscriber generated information to/from another user in association with a call to the user. This information shall be passed transparently (i.e. without modification of contents) through the network. Normally, the network shall not interpret or act upon this information.
The served subscriber can send and receive UUI in different phases of the call depending on the service(s) to which the subscriber subscribes. These services are:
Service 1: UUI can be sent and received during the origination and termination of a call, with UUI embedded within call control messages. The service 1 can be activated implicit by inserting UUI when set-up a call or explicit with an appropriate procedure.
Service 2: UUI can be sent and received after the served subscriber has received an indication that the remote party is being informed of the call and prior to the establishment of the connection. UUI sent by the served subscriber prior to receiving the acceptance of the call by the remote party, may as a network option be delivered to the remote party after the call has been established. The service 2 shall be activated explicitly.
Service 3: User-to-user-information can be sent and received only while the connection is established. The service 3 shall be activated explicitly.
Service 1, service 2 and service 3 shall allow the transmission of UUI with the maximum length of 128 octets per message.
4.2 Applicability to telecommunication services
The applicability of this supplementary service is defined in TS 22.004 .