The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

For the purposes of the present document the abbreviations and acronyms listed in TR 21.905 apply.

A supplementary service modifies or supplements a basic Telecommunication service.

For the purpose of the present document the following terms are defined: Provision An action to make a service available to a subscriber. The provision may be:

• general: where the service is made available to all subscribers (subject to compatibility restrictions enforced) without prior arrangements being made with the service provider;
• pre-arranged: where the service is made available to an individual subscriber only after the necessary arrangements have been made with the service provider.

Withdrawal An action taken by the service provider to remove an available service from a subscriber's access. The withdrawal may be:

• general: where the service is removed from all subscribers provided with the service;
• specific: where the service is removed on an individual basis from subscribers provided with the service.

Registration The programming by the service provider or subscriber of information to enable subsequent operation of a service. The programming action involves input of specific supplementary information. For certain services the registration procedure may cause activation whilst for others the service may already be in the action phase. Erasure The deletion by the service provider, the subscriber or the system of information stored against a particular service by a previous registration(s). Activation An action taken by either the service provider, the subscriber or the system to enable a process to run as and when required by the service concerned, resulting in the active phase. Some services can be either "operative" or "quiescent" (not operative) during the active phase according to whether or not the system would be able to invoke or use the service. Deactivation An action taken by either the service provider, the subscriber or the system to terminate the process started at the activation. Invocation An action to invoke the service required, taken by the subscriber (e.g. pressing a specific button) or automatically by the network or terminal as a result of a particular condition (e.g. calling number identification for each incoming call). Normal operation with successful outcome Description of the normal operation of the service, the normal served subscriber's actions and the system response. Decision points, timing and call progress signals would be some of the aspects defined for the service if they can be perceived by the subscriber. Interrogation The request by the subscriber to the PLMN to provide information about a specific supplementary service. This information can be requested by a:

• status check;
  The following values can be returned by the PLMN:
  • not supported;
  • active and operative;
  • active and quiescent;
  • not active.
  Not all values are applicable to all supplementary services.
• data check;
  This interrogation function compares the data input by the subscriber during an interrogation procedure with the information stored in the PLMN. The PLMN signals an appropriate indication (e.g. "check is positive" or "check is negative").
• data request;
  This interrogation function enables the subscriber to obtain confirmation of her input data. The PLMN signals an appropriate indication (e.g. "the forwarded-to number is etc."). The response to a data request may comprise the status of the service (e.g. not active).

Exceptional operation or unsuccessful outcome Abnormal situations not described in "normal operation with successful outcome". Procedures on time-out, unexpected signalling response and other such events would be defined. Interaction with other supplementary services When more than one supplementary service is active, new logical situations, decisions, priorities, etc., may arise. This subclause would identify and define the resolution of such situations as they affect subscriber perception of the service. Special procedures may therefore be required, e.g. to allow, where possible, the simultaneous use of different supplementary services by one mobile subscriber. Interworking considerations Identification of subscriber perceptions when a call exits from an ISDN/PLMN to another network or enters an ISDN/PLMN from another network (e.g. PSTN). Unstructured SS Operations These operations are characterized by:

• in the mobile to network direction the transparent transport of MMI strings entered by the user to the network;
• in the network to mobile direction the transparent transport of text strings that are displayed by the mobile for user information;
• transparent transfer of data between an application in the MS and a corresponding application in the network.

These operations provide capabilities that can either be used as part of operator specified services, or to facilitate the early introduction of specified services.