A communication system includes: a transmission unit configured to transmit each of a plurality of measurement packets at a predetermined transmission interval; a reception unit configured to receive the plurality of measurement packets which have passed through a predetermined network for a predetermined number of times; and an available bandwidth estimation unit configured to calculate a cumulative value of a queuing delay by using reception time information indicating temporal information about reception of the measurement packets and transmission time information indicating temporal information about transmission of the measurement packets, and estimate an available bandwidth of the network by using the calculated cumulative value of the queuing delay.