There is provided user equipment for communicating with a base station in a mobile communication system supporting LTE including a reception unit configured to receive an indication from the base station to change a sequence number length of an RLC PDU, a re-establishment unit configured to perform re-establishment of an RLC entity upon receiving the indication, and a communication unit configured to use the RLC PDU with the changed sequence number length to communicate with the base station after completion of the re-establishment.