Table 5.1 identifies the information stored by
each of the devices throughout the registration process (during and after).
Establishing a Session in the IMS 117
Various network entities may wish to be alerted whenever a subscriber is registered
or when he/she has a changed registration, for example, an application server that supports
a location-based service (LBS), or a Presence server providing information about
the availability and status of a subscriber. These entities would need to update their
status about the subscriber and therefore should be notified whenever the subscriber
status changes.
This is supported through event notification. The S-CSCF is responsible for sending
event notification to any of the application servers (or other entities within the network)
that have subscribed to the service.
The subscriber??™s device also subscribes to Event Notification, in the event the
subscriber registers the same public user identity with another device (so the
subscriber can receive calls on multiple devices??™ for example). Subscription to Event
notification is achieved using the SUBSCRIBE method with the following headers
and parameters:
?– REQUEST-URI set to the value of the public user identity that the device wants
event notification for
?– FROM header set to the same public user identity as the REQUEST-URI
?– TO header set to same public user identity as the REQUEST-URI
?– EVENT header set to REG
?– EXPIRES header set to 600,000 seconds
?– P-ACCESS-NETWORK-INFO identifying the network type used to access
the IMS
TABLE 5.
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