Network-Based Handover for IMS Service Continuity

The IP Multimedia Subsystem (IMS) has been selected as a telecommunication industrial standard for the signal processing among heterogeneous access networks, and it is also responsible for mobility management. However, the mobility of the user equipment (UE) may disrupt or even intermittently disconnect an ongoing session, which heavily affects the satisfaction of the users. Therefore, how to reduce the service disruption time is an important issue. This paper proposed a network-based handover scheme, abbreviated as NHO, in IMS-based network. When a UE moves to a new network and completes the attach procedure during a mid-session, the access gateway (e.g. PDN-GW in LTE) will send a SIP PUBLISH message with secure context transfer request to the newly attached P-CSCF. Then the new P-CSCF will accomplish the secure context transfer to get the context information of the UE, and then perform the IMS registration procedure and the IMS session setup procedure on behalf of the UE in parallel. The novelty of NHO is that it only requires minor modifications to the attach procedure, and enhances MME, Serving-GW, PDN-GW, HSS, and P-CSCF slightly. Analytical results based on queuing theory show that NHO can shorten the handover delay as compared with current alternatives.