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Back to IP Multimedia Subsystem (IMS)
In this section:
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Overview
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Subscribing to Reg-Event Package
Whenever a registration is successful and support for reg-event package is enabled, the SBC generates subscription requests for the reg-event package. The Subscription is made once for the initial registration, and is unsubscribed when the registration is removed. A subscription may be generated for implicit registrations as well. Even when a registration results in implicit subscription to more than one PUI, SBC subscribes only once for the reg-event package using the default PUI. A subscription to reg-event package expiration time is set to 60 seconds later than the registration expiration interval of the initial Registration.
Routing of Subscribe
The SBC routes SUBSCRIBE depending upon two scenarios.
| Network | SUBSCRIBE Routing | Skip Pattern Matching |
|---|---|---|
| SBC as P-CSCF is in the home network | SBC performs a PSX dip with the DTG and the route received in Service-Route as Route-URI. SBC honors the routes returned by the PSX for routing. | Set |
| SBC as P-CSCF is in the visited network (roaming) | SBC performs a PSX dip with DTG and uses PSX returned route. | Not set |
Routing of the refresh SUBSCRIBE is performed based on the Record-Route header and/or the contact header received in the 200 OK response or the NOTIFY request, whichever came first.
Handling of Notify
On successful subscription to reg-event package, the Notifier sends a NOTIFY request containing the “reginfo+xml” body which contains information about the registration status for the UE. The schema for reginfo+xml is defined in RFC 3680 with some extensions in 24.229. The SBC unpacks and handles the required elements in the reginfo+xml content provided they are received in the correct format. The SBC takes appropriate actions on the Registration based on the XML content.
Refresh SUBSCRIBE
After successful Subscription to reg-event package, SBC periodically sends a refresh SUBSCRIBE under the following conditions:
- Subscription is greater than 1200 seconds – a refresh is sent 600 seconds before subscription expiration
- Initial subscription is 1200 seconds or less – a refresh is sent once half of the subscription has expired
Removal of Subscription to Reg-Event Package
When an error response for a SUBSCRIBE or refresh SUBSCRIBE for reg-event subscription is received, SBC deletes the subscription and does not attempt to resend it. SBC removes a subscription to reg-event package under the following conditions:
- Error response is received
- No response to SUBSCRIBE
- NOTIFY received with Subscription-state of “terminated “
Unsubscribing to Reg-Event Package
The SBC unsubscribes to reg-event package under the following conditions:
- User-Initiated deregistration – On reception of a deregistration request from the User (Register with Expires=0)
- Network-Initiated deregistration – Upon receipt of a NOTIFY request with state attribute of registration elements set to "terminated"
SBC as IBCF or IPX Proxy
When the SBC is configured as an IBCF or IPX Proxy, there is no need for SBC to subscribe to registration event package. In this scenarios, the SBC supports transparently passing SUBSCRIBE-NOTIFY for registration event package, including translating the contact header if needed.
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Overview
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