R6. IMS Registration signalling flow —
Network-initiated deregistration event occuring in the HSS
R6-1. SIP NOTIFY request
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This example assumes that UE1 and P-CSCF1 both have subscribed for the user's registration state event
package and shows how UE1 and P-CSCF1 are notified when the network-initiated
deregistration event occurs in the HSS.
HSS initiates the deregistration, sending a Cx-Deregister (subscriber identity).
After getting the Cx-Deregister message S-CSCF1 immediately sends a NOTIFY request towards
UE1 order to inform about the network initiated deregistration and the subscription termination. The
same Request URI, To, From, Call-ID are used as in the first NOTIFY request. CSeq is incremented
since this is the second NOTIFY request sent towards UE1.