Abstract: A transfer device increments a value of a phase ID at predetermined time intervals, and registers a packet ID of a transmitted data packet and a phase ID on a determination table in an associated manner. When having received a response packet from a receiving-side transfer device, the transfer device determines an unarrived packet on the basis of received packet IDs contained in the received response packet and packet IDs of transmitted data packets. Then, the transfer device determines whether a data packet corresponding to the unarrived packet is lost or on-the-fly from a relationship between a phase ID of the unarrived packet and the maximum phase contained in the received response packet, and retransmits the corresponding data packet only if it is lost.

Abstract: A transfer device allocates, within the range of the maximum communication band of a network that a plurality of groups of applications use in common, a communication band equal to or larger than the minimum band for each of the groups. Furthermore, the transfer device converts, within a communication band allocated to each group, TCP data received from a transmission source of data to UDP data, transfers the UDP data to a transmission destination, and retransmits retransmission data in response to a retransmission request of the UDP data.