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the throughput associated with TCP for the WINDS net-work was 30 Mbps; almost quadruple the throughput as-sociated with CUBIC.When WINDS is set in regenerative mode, it processes received data using ABS (on-board asynchronous transfer mode baseband switch) [4]. To enable compatibility with this process, earth stations transmit uniquely formatted data to the satellite. is format, called an MPEG-TS stream, has been conrmed to be capable of achieving data transmission volume as high as approximately 87.3% of theoretical network bandwidth [7]. e WINDS regenera-tive mode uses the TDMA (time division multiple access) method, which employs superframes composed of 320 slots/frame. In our experiments, we established a line to the satellite which transmitted data using 288 slots, ex-cluding information slots. Actual data rates using the 288 slots were measured at dierent data transfer speed settings (Table 4).e comparison between the throughput measurements in Table 3 and the actual data rates in Table 4 revealed that the general-use CUBIC congestion control algorithms do not allow ecient bandwidth utilization, while the conges-tion control algorithms tuned to WINDS do. In addition, when the CUBIC algorithms were used, it took the com-munication line more than 10 seconds to reach maximum throughput. In comparison, when the algorithms tuned to WINDS were used, it took only three to four seconds.ese results conrmed that congestion control algo-rithms capable of controlling TCP window sizes which account for delay and line status eectively facilitate satel-lite communications that are susceptible to long delays.5.4Transmission characteristics of UDP communicationUnlike TCP communication, UDP communication transmits data without establishing sessions [9]. For this reason, UDP communication is capable of high-speed data processing although it is unable to resend data when packets are lost. We performed data transmission measure-ments associated with UDP communication because this communication mode enabled us to detect packet losses in transmission channels without causing communication delays and to analyze transmission channel capacities. UDP communication measurements using iperf also allowed us TabT4　Theoretical and Actual of data rate for slot setting of 288WINDS link data rateTheoretical value of network bandwidthActual data rate of TCP6Mbps5.105 Mbps4.457 Mbps24Mbps19.143 Mbps16.712 Mbps51Mbps38.286 Mbps33.424 MbpsFiF13Throughput variation of TCP congestion control for WINDS Time [sec] Throughput [kbps] FiF14　Throughput variation of CUBIC Time [sec] Throughput [kbps] WINDS link data rateCongestion controlTCP for WINDSCUBIC6Mbps3.912 Mbps3.731 Mbps24Mbps15.052 Mbps6.851 Mbps51Mbps29.772 Mbps7.774 MbpsTabT3　Comparing of throughput for congestion control3 Ultra-High-Speed Satellite Communication Technology156　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)