ISO/IEC 15050:2003 specifies the signalling protocol for the support of the Advice Of Charge supplementary services (SS-AOC) at the Q reference point between Private Integrated services Network eXchanges (PINX) connected together within a Private Integrated Services Network (PISN).

SS-AOC is a set of supplementary services which enable a user to receive information about the charging of its calls that leave the PISN and enter another network.

The three AOC supplementary services are:

1. Charging information at call set-up time (AOC-S): SS-AOC-S enables the user to receive information about the charging rates at call set-up time and also to receive further information during the call if there is a change of charging rates.
2. Charging information during the call (AOC-D): SS-AOC-D enables a user to receive information on the recorded charges for a call during the active phase of the call.
3. Charging information at the end of the call (AOC-E): SS-AOC-E enables a user to receive information on the recorded charges for a call when the call is terminated.

The Q reference point is defined in ISO/IEC 11579-1.