Patent ID: 7760638

Claim:
A communication system for transmitting and receiving data between a plurality of terminals via a network through a session relay for relaying communication between the terminals, wherein: each of the terminals or the session relay comprises: a measuring portion for measuring a one-way or a round-trip delay time in the network, a determining portion for determining a threshold delay time at which network congestion is judged, and an estimating portion for estimating, with reference to a delay time upon detection of packet loss and the threshold delay time, the possibility that the packet loss is due to congestion, a congestion window being changed with reference to the possibility upon detection of the packet loss, wherein: the estimating portion estimates that the packet loss is due to congestion when the delay time upon detection of the packet loss is greater than the threshold delay time, the estimating portion estimating a smaller possibility that the packet loss is due to congestion as the delay time upon detection of the packet loss is smaller below the threshold delay time.