ETSI: "Handover Requirements between UMTS and GSM or other Radio Systems (3G TS 22.129 version 3.2.0)", European Telecommunication Standard, XX, XX, Dec. 1999, pp. 1-20.
The invention relates to handover of a subscriber unit (301, 305) from a first cellular communication system (201) to a second cellular communication system (203). The first communication system is for example a UMTS communication system supporting a plurality of connections, and the second communication system is for example a GSM communication system supporting only a single connection. The handover comprises forming a handover connection 219 to the subscriber unit (301,305) through the second communication system and handing one of the connections under the first communication system over to this connection. Rather than dropping the remaining connections, they are entered into a holding state. After the handover, one of the connections on hold may be entered into an active state by associating the handover connection (219) with this connection.
25 Claims, 3 Drawing Sheets