3GPP TS 25.331 Section 8.5.6 states that after receiving N313 consecutive "out of sync" indications from layer 1, the UE shall start the T313 timer. Upon receiving N315 successive "in sync" indications from layer 1, the UE shall stop and reset the T313 timer. If T313 expires, a "Radio Link failure" has occurred, and the UE shall drop the call.