The Meaning of SUCCESS

When an operation returns a SUCCESS indication (either synchronously upon function return for synchronous operations, or asynchronously through a LINE_REPLY or PHONE_REPLY message for asynchronous operations), the following is assumed to be true:

• The function has successfully progressed to a point that is defined by the API on a function-by-function basis. After that point has been reached, either the operation is completely finished, or it will be in a state such that independent state messages will inform the application about subsequent progress.

  For example, a service provider's implementation of lineMakeCall should return SUCCESS no later than when the call enters the proceeding call state. Ideally, the provider should indicate SUCCESS as soon as possible, such as when the call enters the dial tone call state (if applicable). Once SUCCESS has been returned to the application, LINE_CALLSTATE messages will inform the application about the progress of the call. Service providers that delay returning the lineMakeCall SUCCESS indication, for example, until after dialing is complete, must be aware that this places that provider at a disadvantage because the usability at the application level may be severely limited. For example, it would not be possible for a user to cancel the call setup request in progress until after dialing is complete and all digits had been sent to the switch.

• Functions that return information (such as lineGetCallInfo) return SUCCESS only when the requested information is available to the application. Functions that return handles (to lines or calls), can return SUCCESS only after the handle is valid. No messages should be sent about that line or call prior to the SUCCESS indication of the function that caused its creation. The service provider is responsible for suppressing such messages.
• Functions that enable certain permanent conditions (such as lineMonitorDigits) return SUCCESS only after the condition is enabled, not when the condition is removed again (for example, not when all digit monitoring has completed).
• Call-control functions (such as lineHold or lineSetupTransfer, but not lineMakeCall) return SUCCESS when the operation is completed. Some telephone networks do not provide acknowledgment (positive or negative) about the completion of certain requests made by service providers. In such situations, the service provider must decide upon success or failure of the request. Therefore, SUCCESS may indicate that the service provider has initiated actions to fulfill the request, but not necessarily anything more. For example, the provider may receive no affirmative acknowledgment to its request from the switch, although it has already sent a success message to the application.