| 摘要 |
A method of enabling the management of handovers of voice calls from a Packet Switched, PS, access to a Circuit Switched, CS, access where the voice calls are established using an IP Multimedia Subsystem, IMS, network. The method comprises performing a first IMS registration of a user via said PS access including setting for the user in a Home Subscriber Server, HSS, of the user's home network, an identifier of a first access transfer control function, which access transfer control function is responsible for anchoring user media sessions in an access transfer gateway of a serving network, and notifying a mobility function within said service network of the set identifier. A second or further IMS registration of the same user is then performed via said PS access, it being determined that said first IMS registration exists. As a consequence, the setting of an identifier of a second or further access transfer control function in the HSS for the user is prevented, while either the setting of the identifier of the first access transfer control function is maintained, or is replaced with an identifier of a service centralization and continuity application server. The mobility function is notified of any change to the set identifier. In the event of a requirement to handover an ongoing voice call associated with said second or further IMS registration from said PS to said CS access, the identifier currently set in the HSS and identified to the mobility function is used to manage the handover.
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