A Bulk Transfer Agent for Improving Data Communication Efficiency in Bullet Trains

High packet loss rate and wide fluctuations of RTT result in poor TCP communication quality. This well-known effect was observed again and more seriously on Internet access using 3G cellular phone systems on high-speed bullet trains, such as Shinkansen, resulting from inappropriate TCP retransmissions caused by RTT fluctuation. To improve data transfer efficiency, we must avoid incorrect TCP retransmissions. For this purpose, we implemented an application gateway called Transfer Agent at each end host on the communication path and a specialized protocol between agents to reduce the number of RTOs. Four different transfer protocols based on FEC (rapid tornado code), retransmission, and DCCP were implemented for inter-agent transmissions. The protocols were tested on our communication emulator, which is based on real communication parameters obtained on a bullet train. For bulk transfer applications, a protocol based on retransmission and a simple congestion control showed the best performance among these protocols, including TCP.