Section: 6.8.4.2 GSM security context
Content: A GSM security context in UTRAN is only established for a GSM subscribers with a R99+ ME. At the network side, two cases are distinguished: a) In case of a handover to a GSM BSS controlled by the same MSC/VLR, the MSC/VLR sends the 64-bit GSM cipher key Kc from the key set used before the intersystem handover to the target BSC (which forwards it to the BTS). b) In case of a handover to a GSM BSS controlled by another MSC/VLR (R99+ or R98-), the initial MSC/VLR sends the 64-bit GSM cipher key Kc from the key set used before the intersystem handover to the BSC via the new MSC/VLR controlling the target BSC. The initial MSC/VLR remains the anchor point throughout the service. If the non-anchor MSC/VLR is R99+, then the anchor MSC/VLR also derives and sends to the non-anchor MSC/VLR the UMTS cipher/integrity keys CK and IK. The non-anchor MSC/VLR stores all keys. This is done to allow subsequent handovers in a non-anchor R99+ MSC/VLR. At the user side, in either case, the ME applies the GSM cipher key Kc from the key set which was used before the intersystem handover.