COMMUNICATION SYSTEM, COMMUNICATION METHOD, RELAY DEVICE, AND MASTER STATION DEVICE

PROBLEM TO BE SOLVED: To make it possible to surely achieve a SLA (Service Level Agreement) of a slave station device on the lower stage side.SOLUTION: A communication system comprises: a first communication network in which a master station device 10 performs uplink multiple access control on a relay device 20; and a second communication network in which a relay device 20 performs uplink multiple access control on a slave station device 30; where the first and second networks are connected through one or a plurality of relay devices 20. A relay device 20 connected to the second communication network grants tag information T1 and T2 for identifying a slave station device 30 that is a transmission source of an uplink data frame transferred from the second communication network to the first communication network to the uplink data frame. The master station device 30 sums up uplink traffic amounts for each slave station device 30 on the basis of the tag information T1 and T2 included in the data frame received from the first communication network.