06-04-2012, 02:44 PM
Long Distance Satellite Telephone (LDST)
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Introduction
This is a satellite based communication system that provides a single channel two way voice/fax communication from the remote location with all parts of the world. Thus the projects do not have to rely on P&T lines for making calls which are unreliable keeping in view the terrain of the project. LDST scheme was launched by DOT in late 1994. Under this scheme, remote areas can be connected to the nearest Regional Hub through satellite link. The salient feature of this scheme is that, for example, the satellite telephone located in the Northern Region will be equivalent to Delhi telephone placed at the remote location. Hence all calls to and fro from this phone to Delhi/ NCR shall be treated as local calls as Delhi telephone number is provided for LDST-s located in Northern Region. For any other location, STD code precedes the number in a similar fashion as we make calls from a Delhi telephone. With special recommendation of the DoT, Delhi hub has been temporarily allocated for LDST at Loktak, which pertains to North-Eastern region (Shillong hub). Presently 11 LDST-s are operational at various projects, 3 LDST-s are in the process of installation and 8 LDST s are in the process of procurement. In LDST-s, 4.8 Kbps bandwidth is available for voice and 9.6 Kbps bandwidth for fax transmission.
Component of LDST
Indoor Unit:
SCPC modem
Ring Frequency Generator card
TELLABS 2W/4W converter
Echo Canceller card
Ringer Card
Indoor power supply unit
Outdoor Unit:
m antenna
Solid State Power Amplifier (SSPA)
Radio Frequency Transceiver (RFT)
Outdoor Power Supply Unit (PSU)
In India, calls from the LDST are routed via INSAT-3A satellite to the regional hub (Sikenderabad Hub in present case), then through coaxial to MTNL and then to the desired destination.