Section: 6.8.5.2 GSM security context
Content: Handover from GSM BSS to UTRAN with a GSM security context is possible for a GSM subscriber with a R99+ ME or for a UMTS subscriber with a R99+ ME when the initial MSC/VLR is R98-. At the network side, two cases are distinguished: a) In case of a handover to a UTRAN controlled by the same MSC/VLR, UMTS cipher/integrity keys CK and IK are derived from the 64-bit GSM cipher key Kc used before the intersystem handover (using the conversion functions c4 and c5) and sent to the target RNC. In case of subsequent handover in a non-anchor R99+ MSC/VLR, a 64-bit GSM cipher key Kc is received for a UMTS subscriber if the anchor MSC/VLR is R98-. b) In case of a handover to a UTRAN controlled by another MSC/VLR, the initial MSC/VLR (R99+ or R98-) sends the 64-bit GSM cipher key Kc used before the intersystem handover to the new MSC/VLR controlling the target RNC. That MSC/VLR derives UMTS cipher/integrity keys CK and IK which are then forwarded to the target RNC. The initial MSC/VLR remains the anchor point for throughout the service. At the user side, in either case, the ME derives the UMTS cipher/integrity keys CK and IK from the 64-bit GSM cipher key Kc (using the conversion functions c4 and c5) which was used before the intersystem handover and applies them.