Mid-Session Macro-Mobility in IMS-Based Networks

With the introduction of terminals that support multiple access technologies, macro-mobility and roaming are becoming even more important functionalities: it is expected that mobile terminals will handover between heterogeneous networks in order to extend coverage or to get connectivity to faster and/or cheaper access technologies. Access and session control must be guaranteed when roaming across different administrative domains. The 3GPP IP multimedia subsystem (IMS) is the first platform standardized towards network-independent access and session control. However, the current IMS specifications do not allow for any change of the user´s IP address during a session, which prevents seamless mid-session macro-handover. In this paper, we present and compare a set of solutions, implemented respectively at the session and network layers, for shortening the handover delays and/or providing session continuity in case of macro-handover in IMS-based networks. Since one of the main functions of IMS is quality of service (QoS) negotiation and the control of legacy interfaces to the access networks for QoS provisioning, special attention is given to the discussions of the QoS re-negotiation procedures during such handover cases.