A method for transmitting, by a transmission entity, a packet in a system, according to an embodiment of the present invention, comprises the steps of: transmitting an automatic repeat request (ARQ) configuration (AC) message including ARQ configuration information; receiving an ARQ feedback (AF) message indicating that one or more packets are lost, the AF message including information on a propagation delay for packets to arrive at a receiving entity; identifying a delivery time of the packets between the receiving entity and the transmitting entity based on the propagation delay included in the AF message; and determining whether to transmit one or more lost packets based on the delivery time.