SECURITY MODE UPDATES DURING CELLULAR RELOCATION TO AVOID CALL DROP

摘要

An undesired call drop in a UMTS network can be avoided during a relocation procedure when a UE fails to receive a certain acknowledgment message. When the UE undertakes a concurrent routing area/location area (RA/LA) update procedure corresponding to a circuit-switched (CS) call and a packet-switched (PS) call, a security mode update procedure occurs. For the CS domain, a first security message including ciphering information is transmitted to the UE, and the UE responds. If an ACK message for this response is not received, but the UE receives a second security message including ciphering information for the PS domain, rather than dropping the PS call and transmitting a failure message, the UE treats the second security message as a substitute for the ACK. The UE then processes the second security message normally.