Patent ID: 6963745

Claim:
A method for performing inter system handovers in a mobile telecommunication system, wherein a handover process is performed when a dual mode user equipment (UE), capable of communicating in both a GSM (Global System for Mobile communication)/GPRS (General Packet Radio Service) network and a UMTS (Universal Mobile Telecommunications System) network, connects a dedicated channel and sets up a call in a BSS (Base Station Subsystem) region where the GSM/GPRS provides coverage, and then moves to a UTRAN (UMTS Terrestrial Radio Access Network) where the UMTS provides coverage, the method comprising the steps of: if the dual mode user equipment (UE) receives an inter system handover command, to handover from the BSS to the UTRAN, requesting, at a sublayer RR (Radio Resource) of GSM/GPRS network layer in the UE, a GSM/GPRS data link layer to suspend a GSM/GPRS data link, requesting a GSM/GPRS physical layer to release a physical channel of the GSM/GPRS, and sending the handover command between systems to the UTRAN for authorizing a sublayer RRC (Radio Resource Control) of UMTS network layer in the UE to continue calls; requesting, at the RRC in the UE, a UMTS physical channel to be configured as a UMTS physical channel, and monitoring if the UMTS physical layer succeeds to configure the UMTS physical channel as requested; if the UMTS physical layer succeeds to configure the UMTS physical channel, requesting, at the RRC in the UE, a UMTS data link layer to configure a UMTS data link, and conveying information to the UTRAN through a UMTS channel that the handover between systems from the BSS to the UTRAN has been successfully performed; and sending, at the RRC in the UE, a GSM/GPRS resource release message to RR/GRR of the UE, thereby resetting the GSM/GPRS physical layer and the GSM/GPRS data link layer.