Section: 5.2a Maintenance of UL Synchronization
Content: If upper layer informs that the UL synchronization is lost according to the clause 5.3.18 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8], the MAC entity shall: - flush all HARQ buffers; - not perform any uplink transmission. If upper layer informs that the UL synchronization is restored for the SpCell according to the clause 5.3.18 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8], uplink transmissions can be performed. NOTE: The MAC entity suspends all UL operations (e.g. stop RACH, SR, and UL HARQ operation) after receiving the indication of an uplink synchronization loss and resumes the operation when receiving an indication of uplink synchronization.