<xhtml:p>This asynchronous operation is called by the Web Service to
notify the watcher (application) that the subscription has terminated.
Typical reasons are a timeout of the underlying SIP soft state
subscription (in accordance with [14] and [9]) or the decision of
the presentity to block further presence information to that
watcher. Since the subscription request has no expiration
parameters, the service implementation may provide an inactivity
timer that also triggers the subscriptionEnded message.</xhtml:p>