R3. IMS Registration signalling flow —
UE subscription for registration state event package
R3-3. SIP NOTIFY request
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S-CSCF1 sends a first NOTIFY request towards UE1 in order to inform UE1 about the registration status of the monitored user.
In the example below, the NOTIFY request specifies the following public user identity as registered (i.e. status=open): sip:firstname.lastname@example.org, tel:+358504821437.
The following public user identity has been deregistered (i.e. status=closed) sip:email@example.com. They are arranged in the preferred order of priority in this example.