Proactive Handover in Heterogeneous Networks Using SIPs

In some areas, overlapping networks provide alternative wireless links like WLAN, GSM, 3G etc. Ideally, the user should be connected to the most attractive network any time according to predefined priorities. This is accomplished with automatic handover. The most likely commercial application of this type is designed for speech, and is using SIP to set up VoIP calls through WLAN networks or mobile networks. To make the handover time as short as possible is essential to make it attractive. This is best done by preparing the alternative networks before the handover is needed. This is called proactive handover. This paper suggests changes to some of the basic SIP messages that open for proactive handover in SIP and help reduce the delays when roaming.