- 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.