how can we terminate our tsapi link and unregister all our devices we are monitoring in a timely manner i.e. we have 400 phones and need to shutdown, our link gets terminated before we can finish unregistering all our phones

Ending a TSAPI session will have no effect on registered phones - I take it that you meant ending a DMCC session.

When a DMCC session is ended gracefully by sending a StopApplicationSession, any phones that are registered by the session will be unregistered by the AE Services.

If you want to control the unregistrations, you should not close the DMCC session until after all the devices are unregistered.

Martin