"This standard defines the stage two of the Advice of Charge (AOC) supplementary service for the pan- European Integrated Services Digital Network (ISDN) as provided by the European public telecommunications operators. Stage two identifies the functional capabilities and the information flows needed to support the service description. The stage two description also identifies user operations not directly associated with a call (see CCITT Recommendation I.130 [1]). This standard is defined according to the methodology specified in CCITT Recommendation Q.65 [2]. In addition this standard does not specify the requirements 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 defines 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 AOC supplementary service provides the served user with usage based charging information. The AOC supplementary service is applicable to all circuit switched telecommunication services. This standard is applicable to the stage three standards for the ISDN AOC supplementary services. The term ""stage three"" is defined in CCITT Recommendation I.130 [1]. Where the text indicates the status of a requirement@ i.e. as a strict command or prohibition@ as authorisation leaving freedom@ as a capability or possibility@ this shall be reflected in the text of the relevant stage three standards. Furthermore@ conformance to this standard is met by conforming to the stage three standards with the field of application appropriate to the equipment being implemented. Therefore@ no method of testing is provided for this standard. This standard does not formally describe the relation between this supplementary service and the basic call@ but where possible@ this information is included for guidance."