Aastra 9617 Online User's Manual page 324

You can also program the Don't Disturb key into a
memory key so you can quickly turn it on and off, even
while your telephone is ringing.
For more information, refer to the following topics:
Adding and using a Don't Disturb key
page 325
Deleting the Don't Disturb key
Turning DND on or off
on page 326
on page 328
on
324