Provided are a data transmission system, an encoding apparatus, and a decoding method. The encoding apparatus includes an encoding unit configured to use an encoding matrix to encode original packets sequentially generated from a codec to generate an encoded packet in units of a generation. The encoding unit is configured to use information provided from the codec to dynamically determine a generation boundary of the original packets to encode the original packets. The encoding unit is configured to dynamically a generation size according to a generation time of the original packets. According to embodiments of the inventive concept, it is possible to use information provided from a VoIP codec to dynamically determine the boundary or size of a generation to decrease a standby time upon encoding/decoding, and may recover the loss of packets that may occur in a wired/wireless network.