R7. IMS Registration signalling flow —
Network-initiated deregistration upon UE roaming and registration to a new network
R7-1. SIP REGISTER request (via P-CSCF2)
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This shows the registration signalling flow for the scenario that UE1 loses the GPRS attachment in current
visited access network and roams to makes a new GPRS attachment in a new visited access network without
deregistration from its previous network. When
UE1 starts registration via the new visited access network and P-CSCF2, the home S-CSCF in the home IMS
network initiates the deregistration to P-CSCF1 in the previous visited network. It is assumed that the old P-CSCF
has subscribed the event package to the S-CSCF and the subscription has not expired.
For the reason of
simplicity, the authentication procedure is not shown because it has no technical impact on this flow.