This Recommendation defines the operation of the Digital Subscriber Signalling System No. 1 (DSS 1) for the support of the Advice Of Charge (AOC) Supplementary service at the T or the coincident S and T reference point of the User‑to‑Network Interface of the Integrated Services Digital Network (ISDN).
The Advice Of Charge supplementary service allows the served user to request the network to provide charging information at call establishment time (AOC-S), during the call (AOC-D), or at the end of the call (AOC-E). Depending on the subscribed options, this charging information may be provided either for all calls or only for the calls for which an explicit request is made.