Section: 4.4.3.5 NAS COUNT wrap around
Content: If, when increasing the NAS COUNT as specified above, the MME detects that either its downlink NAS COUNT or the UE's uplink NAS COUNT is "close" to wrap around, (close to 224), the MME shall take the following actions: - If there is no non-current native EPS security context with sufficiently low NAS COUNT values, the MME shall initiate a new AKA procedure with the UE, leading to a new established EPS security context and the NAS COUNT being reset to 0 in both the UE and the MME when the new EPS security context is activated; - Otherwise, the MME can activate a non-current native EPS security context with sufficiently low NAS COUNT values or initiate a new AKA procedure as specified above. If for some reason a new KASME has not been established using AKA before the NAS COUNT wraps around, the node (MME or UE) in need of sending a NAS message shall instead release the NAS signalling connection. Prior to sending the next uplink NAS message, the UE shall delete the eKSI indicating the current EPS security context. When the EIA0 is used as the NAS integrity algorithm, the UE and the MME shall allow NAS COUNT wrap around. If NAS COUNT wrap around occurs, the following requirements apply: - the UE and the MME shall continue to use the current security context; - the MME shall not initiate the EPS AKA procedure; - the MME shall not release the NAS signalling connection; and - the UE shall not perform a local release of the NAS signalling connection.