ENS is an alarm dispatcher. This decouples alarm delivery from alarm generation. It also enables the use of multiple delivery methods, such as email and wireless communication. The csadmind daemon detects events by sensing changes in the state of the alarm queue. The alarm queue’s state changes every time an alarm is placed in the queue. An alarm is queued when a calendar event generates an alarm. The following URIs represent these kind of events:
for todos (tasks):
calid is the calendar ID.
uid is the event/todo (task) ID within the calendar.
rid is the recurrence id for a recurring event/todo (task).
aid is the alarm ID within the event/todo (task). In case there are multiple alarms, the aid identifies the correct alarm.
The publisher csadmind dequeues the alarms and sends notifications to enpd. The enpd daemon then checks to see if anyone is subscribed to this kind of event and sends notifications to the subscriber, csnotifyd, for any subscriptions it finds. Other subscribers to alarm notifications (reminders) can be created and deployed within an Calendar Server installation. These three daemons interacting together implement event notification for Calendar Server.