| Level | Code | Display | Definition |
| 1 | D | deferred |
The receiver may respond in a non-immediate manner. Note: this will be the default value.
|
| 1 | I | immediate |
The receiver is required to assume that the sender is blocking and behave appropriately by sending an immediate response.
|
| 1 | Q | queue |
The receiver shall keep any application responses in a queue until such time as the queue is polled.
|