# Invoking advice of charge services

If AOC services are not provided using a subscription service, they must be invoked to be used. Invocation of the services at the originating node is accomplished on a per-call basis. To invoke AOC services, an ACU_CONN_RQ primitive is sent to the stack, containing an acu_ss_aoc_request_invoke extended data structure.

## Successful AOC invocation

If AOC services are successfully invoked, an acu_ss_aoc_request_ret_result extended data structure is returned in an ACU indication or confirmation message.

The application may receive one acu_ss_aoc_request_ret_result message indicating the activation of all AOC services, or one for each service. If the application receives a message indicating that not all requested services are activated, this does not necessarily imply an error. It may mean that results are not yet available for the other services. Subsequent messages contain the activation results for these services.

## Unsuccessful AOC invocation

If AOC services are not successfully invoked, an acu_ss_aoc_request_ret_error extended data structure is returned in an ACU indication or confirmation message.

AOC request procedure during call establishment