A data transmission system includes: a data generation device generating data in each time slot; a wireless access device; a proxy device interconnecting the data generation device and the wireless access device via wired network; and a mobile device connected to the wireless access device via wireless network and receiving the generated data. The proxy device includes in a packet the generated data in each time slot or the difference of the generated data between each time slot and a reference time slot associated therewith to generate a packetized data in accordance with data loss rate and data transmission delay in the wireless network and sends the packetized data to the wireless access device. The wireless access device determines an upper limit of retransmissions of the packetized data for the mobile device in accordance with the data loss rate and the data transmission delay in the wireless network.