A data communication system includes a mobile station capable of receiving data communications directed to the mobile station, at least one relay station capable of relaying data between a base station and the mobile station, and the base station capable of assigning a connection identifier to the mobile station and each of the at least one relay station and sending a protocol data unit through the at least one relay station to the mobile station, the protocol data unit being capable of identifying the connection identifier assigned to the mobile station without identifying the connection identifier assigned to the at least one relay station.