fiber optical converter transmits the digital pulse codes for 0—60Km through optical fibers. The MODEM is widely used in various spot data communication such as SCADA system, data collecting system, computer distributing system, and so on. The OTS232 can compose star network, ring network or simple point-to-point system. Taking no participation to the communication protocols between data equipment, OTS232 transmits transparent channels in point to point mode.