VoIP mobility in IP/cellular network internetworking

This article explores VoIP mobility in the context of IP and cellular netwo rks interworking. ITU-T Rec. H.323 gateways provide the interconnection bet ween IP networks and switched circuit networks. They allow a call originati ng from an SCN phone to be transmitted over an IP network to an H.323 termi nal, or bridged to another SCN phone. While H.323 provides interoperability with other SCN terminals, the major efforts have been focused on IP/wired SCN (PSTN, ISDN, etc.) interworking. In this article we discuss the challen ges associated with the interworking between IP networks and cellular netwo rks through H.323 gateways, and propose an innovative approach using the ex isting call transfer supplementary service to provide VoIP mobility in the H.323 IP telephony networks. The proposed approach uses existing components in the H.323 standard, thereby allowing VoIP mobility service in hybrid IP /cellular networks to be a value-added feature in the existing H.323-compli ant Internet telephony systems.