DATA TRANSMISSION FROM SEISMIC STATIONS VIA NETWORK AGNES USING GSM-GPRS TECHNOLOGY
Jaromír Knejzlík · 2004
Global System for Mobile Communication (GSM) is frequently used for data transmission from seismic stations because it allows an easy realization of data connection from field observation points where metallic telephone line isn’t available. Communication channel is established as a dial-up connection. As a GSM communication adapter either separate GSM modems or modems integrated to some standard mobile phone are used. Data are transferred through GSM network the same as voice digital signal using service Circuit Switched Data (CSD), but the priority of data is lower. Therefore data rate fluctuates according to the load of GSM network and theoretical value of 9.6 kbps (14.4 kbps Eurotel) is achieved rather rarely. Moreover, this way of data transfer is expensive with regard to a high price of CSD service. To reach low-cost access to Internet from mobile phone the GSM network was supplemented by General Packet Radio Service (GPRS). The GPRS technology allows usage of associated free channels of CSD system and data packet switching technology for data transfer. It allows users to stay continuously connected to the Internet. Data rate is theoretically higher on CSD, in practice it considerably depends on network loading. The main advantage is that GPRS user pays only for the amount of transferred data, not for online time per-minute. In the paper principles of GPS, GPRS and telemetric data transmission using GPRS are briefly described. System of seismic data transmission from PCM3-EPC apparatuses with the help of virtual private network (VPN) AGNES, operated by company Conel Ltd. in the GPRS T-Mobile network, is tested in the Institute of Geonics AS CR. Communication adapters (which convert PPP protocol to RS232 protocol), the CGU02 Intelligent GPRS modems (Conel Ltd.) and communication software pcAnywhere are used. Our experience obtained during the trial operation is discussed.