The present document specifies the stage three Protocol Description of the Advice Of Charge (AOC) service, based on stage 1 and 2 of the ISDN Supplementary Service Advice Of Charge for all calls (permanent mode). It provides the protocol details in the IP Multimedia (IM) Core Network (CN) subsystem based on the Session Initiation Protocol (SIP) and the Session Description Protocol (SDP). Three AOC services exist:

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

The present document is applicable to User Equipment (UE) and Application Servers (AS) which are intended to support the AOC supplementary services.

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.
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• 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.