3.1.5.2.2 Two-Way Requests
If this event occurs while the client is in the Accepting Requests state, the client moves into the Sending Request state and sends the request to the server. Otherwise, the event is queued until the client returns to the Accepting Requests state. (See figure in section 3.1.)
When the event has been sent to the server, the client moves to the Receiving Response state. The client returns to the Accepting Requests state when the response has been received. The return value is the one received from the server, or an appropriate error code from the set of DSLR error codes defined in section 2.2.2.5.