HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

Event Notification 231
SIP Stack Event Notification Feature
request must include an Expires header that determines the
duration of the subscription.
2. The Notifier acknowledges the subscription with a 200
response. It can shorten the subscription expiration by setting a
lower value to the Expires header.
3. Upon successfully accepting the subscription, the notifier
sends a NOTIFY message immediately to communicate the
current resource state to the subscriber, or just as a
confirmation of the subscription.
4. NOTIFY messages are sent to inform subscribers of changes in
state. (This is actually the purpose of the subscription).
5. In order to increase the subscription duration, the subscriber
sends a refresh SUBSCRIBE request, with a new expiration
value.
6. Immediately the notifier sends a NOTIFY message. (See step
2).
7. When the subscriber wishes to unsubscribe, it initiates a
SUBSCIRBE request with an expiration value of zero.
8. The Notifier accepts the UNSUBSCRIBE request with a 200
response.
9. The Notifier sends a NOTIFY request indicating that the
subscription was terminated.
SIP STACK EVENT
N
OTIFICATION
F
EATURE
The SIP Stack Event Notification Feature is responsible for creating,
maintaining and terminating subscription. Subscriptions are responsible for
sending and receiving notifications about events. A subscription can be
established by sending a SUBSCRIBE request. However, additional ways exist
for establishing subscriptions. For more information, see Out-of-Band
Subscription.
Each subscription can hold several notifications. A notification is always
created using a NOTIFY message. A subscription uses an Event header to
declare the event type that should get notifications about its state changes. This
Event header is also used to match incoming notifications to their subscription,
and therefore this header must be present in all request messages of this
subscription.