Vol. 41 No Fig. 1 SCS Data transmission network on SCS. HDTV H.261 RGB NTSC VSAT VSAT VSAT 1 HUB VSAT 8) 9) FECForward Error Correction HUB

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1 Vol. 41 No. 10 Oct SCS VSAT SCS VSAT VSAT 1.5 Mbps 1.3 Mbps Data-sharing on Inter-university Satellite Network Kikuo Asai, Noritaka Osawa, Kimio Kondo, Kiyohiro Yuki and Katsuaki Yoshida We developed a multicast file transfer system which is used for data-sharing services as extension of the inter-university satellite network (Space Collaboration System: SCS). With data-sharing among VSATs (Very Small Aperture Terminals), the service can provide an opportunity of effective distance education to SCS users in computer network. To make good use of SCS sufficiently, we focus on material transmissions during a session exchanging audiovisual signals, and develop the file transfer system connected to the link control system. It is important to reuse present resources and to have systematic flexibility in installing the system to each VSAT. Then, signal multiplex function of a CODEC makes it possible to select a link-speed bandwidth. The developed system is actually implemented to the VSATs, and an experiment is made to evaluate its performance. The results show the smooth file transfers and works of each function. The transmission rate is obtained up to 1.3 Mbps including headers in the link-speed of 1.5 Mbps, which indicates efficient use of the link-speed bandwidth. 1. 1) 4) SCSVSAT 5) National Institute of Multimedia Education NEC Co., Ltd. 140 SCS VSAT 6) SCS SCS 7) X 2782

Vol. 41 No. 10 2783 1 Fig. 1 SCS Data transmission network on SCS. HDTV H.

2 Vol. 41 No Fig. 1 SCS Data transmission network on SCS. HDTV H.261 RGB NTSC VSAT VSAT VSAT 1 HUB VSAT 8) 9) FECForward Error Correction HUB- VSAT 10),11) 13),14) SCS SCS 5) 17.5 SCS CODEC OS SCS 15) IP 11),16) VSAT TCP 17),18) FTP 19) SCS 2 SCS

3 2784 Oct SCS 2.1 SCS SCS 2.2 8),12) 1 VSAT SCS 2.3 SCS VSAT 1 Table 1 one-to-many Comparison of the fixed and dynamic one-tomany topology. Topology Sender Link Control Feature Static Fixed No Need Simple Dynamic Any Necessary Flexible 1 VSAT VSAT VSAT 2 4 CODEC VSAT (1) (2) (3) kbps

4 Vol. 41 No SCS 6.54 db 5) Ku 20),21) % 99.80% VSAT Y S t P P = Y S t P e (1) P e P e = qdc (2) q dc MODEM 22) % 1% M Fig. 2 Channel Rate 2 VSAT Configuration of the VSAT station. 2 SCS Table 2 Data-sharing in SCS. Two, Three, Four 1536, 768, 512, 384, 256, 128, 64 kbps 2 VSAT Data Transmission SystemData Transmission ControllerData Tx-Rx Manager 3.1 SCS MODEM 1536 kbps MODEM CODEC CODEC kbps 2 SCS 3.2 SCS SCS

5 2786 Oct kbps (1) Connection Switch for Data Transmission (2) Router for Data Transmission (3) 1 UNIX Windows NT OS 3 HUB VSAT MODEM Data Transmission ControllerData Tx-Rx Manager Data Transmission Control APP FTP FTP Server 3 Fig. 3 System architecture. Link Control System FTP kbps CODEC MODEM 768 kbps CODEC MODEM CODEC AV Controller 4 CODEC

6 Vol. 41 No Fig. 4 User interface of link control system. HUB (a) (b) 3.2 (1) 5 Fig. 5 User interface of data transmission control system.

7 2788 Oct / / (2) FTP VSAT LAN FTP 6 TCP VSAT VSAT FTP Fig. 6 6 Illustrative example of file transfer.

8 Vol. 41 No RTP 23) RTCP 23) UDP FIFO VSAT FTP VSAT HUB Fig. 7 7 Control on collision of transmission requests. VSAT VSAT HUB VSAT 7 VSAT HUB VSAT HUB VSAT VSAT 4.3.3

9 2790 Oct SCS MODEM CPU: 400 MHzOS: Linux CPU: 400 MHzOS: Windows NT4.0 LAN 100 Mbps Ethernet 1406 k 1k 8 65% Q s t Q = s/t B = s b +d r +d u +d h +b i s b + h i+d c +d u (3) +d h s d B s b s d d r RTP d c RTCP h i d u UDP/IP d h HDLC b i HDLC 8 Fig. 8 Throughput characteristics. 3 Table 3 Result of file transfer experiment. Link Speed [kbps] Size [kbyte] Troughput [kbps] RTP RTCP 28 UDP/IP 28 HDLC 8 LAN 10% 6222 k ASCII 1310 kbps 98% kbps 40 M

10 Vol. 41 No CODEC 6. SCS SCS 1 CODEC VSAT SCS 1 SCS VSAT SCS SCS

2792 Oct. 2000 1) Vol.40, No.1, pp.161 167 (1999). 2) Vol.39, No.2, pp.199 210 (1998). 3) Vol.39, No.2, pp.447 457 (1998). 4) Vol.J80-B-I, pp.244 265 (1997). 5) Vol.J82-D-I, pp.581 588 (1999).

11 2792 Oct ) Vol.40, No.1, pp (1999). 2) Vol.39, No.2, pp (1998). 3) Vol.39, No.2, pp (1998). 4) Vol.J80-B-I, pp (1997). 5) Vol.J82-D-I, pp (1999). 6) SCS Vol.J82- D-I, pp (1999). 7) No.1, pp (1998). 8) 11 (1999). 9) Lin, S., Costello Jr., D.J. and Miller, M.J.: Automatic-repeat-request error-control schemes, IEEE Commun.Mag., Vol.22, pp.5 16 (1984). 10) Arora, V., Sphasindhu, N. and Baras, J.S.: Asymmetric internet access over satellite-terrestrial networks, AIAA CP, pp (1996). 11) Nakayama, M., Nakagawa, M., Hashimoto, Y., Tanaka, K. and Nakashima, H.: A satellite communication system for interactive multimedia networks, IEICE Trans. Commun., Vol.E80-B, No.1, pp (1997). 12) Maral, G.: VSAT networks, John Wiley & Sons (1995). 13) SkyPerfecPC. 14) MegaWave. 15) Vol.J81-B-II, No.5, pp (1998). 16) ATM /IP Vol.J81-B-II, No.5, pp (1998). 17) VSAT SAT99-11, pp (1999). 18) TCP SAT99-77, pp (1999). 19) VSAT FTP Vol.J80-B-II, No.10, pp (1997). 20) ITU-R: Propagation data and prediction methods required for the design of Earth-space telecommunication systems, Recommendations on radiowave propagation, p (1999). 21) Karasawa, Y. and Matsudo, T.: One-minute rain rate distributions in Japan derived from AMeDAS one-hour rain rate data, IEEE Trans. Geoscience and Remote Sensing, Vol.29, No.6, pp (1991). 22) (1997). 23) Schulzrinne, H., Casner, S., Frederick, R. and Jacobson, V.: RTP: A transport protocol for real-time applications, Audio-Video Transport Working Group, RFC 1889 (Jan. 1996). ( ) ( ) 3 8 9

12 Vol. 41 No ACMIEEE-CS V 4 SCS 3 39 PCM SI

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