Section: 5.3.6.3 Reception of the CounterCheck message by the UE
Content: Upon receiving the CounterCheck message, the UE shall: 1> for each DRB that is established: 2> if no COUNT exists for a given direction (uplink or downlink) because it is a uni-directional bearer configured only for the other direction: 3> assume the COUNT value to be 0 for the unused direction; 2> if the drb-Identity is not included in the drb-CountMSB-InfoList: 3> include the DRB in the drb-CountInfoList in the CounterCheckResponse message by including the drb-Identity, the count-Uplink and the count-Downlink set to the value of TX_NEXT – 1 and RX_NEXT – 1 (specified in TS 38.323[ NR; Packet Data Convergence Protocol (PDCP) specification ]  [5]), respectively; 2> else if, for at least one direction, the most significant bits of the COUNT are different from the value indicated in the drb-CountMSB-InfoList: 3> include the DRB in the drb-CountInfoList in the CounterCheckResponse message by including the drb-Identity, the count-Uplink and the count-Downlink set to the value of TX_NEXT – 1 and RX_NEXT – 1 (specified in TS 38.323[ NR; Packet Data Convergence Protocol (PDCP) specification ]  [5]), respectively; 1> for each DRB that is included in the drb-CountMSB-InfoList in the CounterCheck message that is not established: 2> include the DRB in the drb-CountInfoList in the CounterCheckResponse message by including the drb-Identity, the count-Uplink and the count-Downlink with the most significant bits set identical to the corresponding values in the drb-CountMSB-InfoList and the least significant bits set to zero; 1> submit the CounterCheckResponse message to lower layers for transmission upon which the procedure ends.