Method and apparatus for providing immediate ciphering after an inter-system UTRAN-GSM handover

摘要

Disclosed is a method for performing an inter-system handover. The method triggers the handover of a mobile station (100) from a UTRAN system to a GSM system by sending a HANDOVER FROM UTRAN COMMAND message from the UTRAN system. For the case where a HANDOVER COMMAND is sent transparently with the HANDOVER FROM UTRAN COMMAND, where the HANDOVER COMMAND has an information element set for indicating that ciphering is to be started, the method begins data ciphering immediately after handing over to the GSM system such that the first data frame transmitted by the mobile station in the GSM system is a ciphered data frame. For the case where there is a pre-existing UTRAN system ciphered data connection when the HANDOVER FROM UTRAN COMMAND message is received, the method continues without interruption the use of data ciphering with the data connection after handing over to the GSM system.