Indian Railways VSAT Network

• VSAT (Very Small Aperture Terminal) networks provide point-to-point or point-to-multipoint data connectivity using geostationary satellites as repeaters.
• In Indian Railways, VSAT networks are used for UTS/PRS, FOIS connectivity, and accident site communication (voice, data, video).
• They provide connectivity where normal means are unavailable or not feasible.

IR VSAT Network Components

• The Indian Railway VSAT network uses a star architecture.
• It consists of:
• Hub Earth Station
• Remote Earth Station
• Satellite Transponder & Space Link
• Network Control Centre
• Interface Equipment
• The network provides transparent transmission links compatible with any network using suitable interface equipment.
• The IR satellite network operates in the Ku Band.
• Uplink frequency: 13.75 to 14.5 GHz
• Downlink frequency: 10.70 to 12.75 GHz
• Uplink frequency is the carrier frequency for transmissions from the hub or remote earth station to the satellite.
• Downlink frequency is the carrier frequency for satellite transmissions to the hub or remote earth station.

Hub Earth Station

• IR's current hub earth station is located in New Delhi.
• It is the central point of the entire network.
• Communication between remote sites or from remote sites to external networks is established through the hub earth station.
• Responsibilities include:
• Collecting data from enterprise LANs
• Address translation
• Converting data into IF and RF signals for satellite transmission to remote earth stations/terminals
• Maintaining integrity checks
• Time synchronization for all remote earth stations
• Satellite tracking
• Converting RF received from remote sites into data signals for enterprise-level delivery
• The NDLS Satellite Hub has been upgraded to HX Satellite technology.

Salient Features of HX Network

• Network efficiency - The new configuration can provide 12Mbps out-route and 7.4Mbps in-route from currently 6.5Mbps & 5.1Mbps respectively.
• Indian railways will get 65% more bandwidth
• Bandwidth - Large bandwidth pool availability for all users after going on a single network.
• Troubleshooting - Single window troubleshooting,
• Mobility solution - HX platform supports mobility applications, HX 200 modem is capable of collecting Lat Long parameters automatically through GPS.
• Advanced Technology - HX network works over DVB-S2 with Adaptive Coding Modulation (ACM).
• AIS - Adaptive Inroute Selection (AIS) for maximum bandwidth efficiency.
• QoS - Service level control provides the ability to have multi-level QoS offerings.
• Flexibility in configuration - it allows flexible configurations with multiple networking topologies - star, mesh, and multi-mesh.
• CIR - Each remote link can be configured with Committed Information Rates (CIRs).
• Capability - It can work over 02 different transponders on the same satellite for a single network.

Signal Transmission

• The transmission of a signal up to the satellite and back down is called a hop.
• Transmission delay for one hop is 240-270 milliseconds.
• Railway has hired 12 MHz frequency space on GSAT 18 for their VSAT Network.
• To determine the availability of satellite communication, a link budget calculation is performed.
• The calculation considers satellite power, antenna size, and transponder sizing.
• All transponder space is allocated by the Department of Space.

Remote Earth Station Components

• A parabolic antenna.
• An outdoor unit (ODU) containing a Block Up Converter (BUC) to transmit and a Low Noise Block (LNB) to receive signals.
• An indoor unit.
• Power supply arrangements.
• Protection and earthing arrangements.
• Indoor unit interacts with the Antenna System and external data devices through Ethernet LAN ports.
• Remote installations require latitude and longitude information for location relative to the satellite and hub earth station.

Interface Equipment

• The VSAT network interfaces with external data devices using router or router switch combinations at hub earth stations.
• At remote stations, Ethernet LAN output is a standard interface for direct connection to devices with Ethernet.
• Application servers like FOIS, IP Exchange, MPEG, and web servers are interfaced with the VSAT network via a router switch combination.

Network Control Center

• The Network Control Center administers and manages the VSAT network and its applications.
• This is done using a Network Management System (often SNMP-based) and other tools.
• It generates analysis reports for network operations.
• Analyzing traffic flow and taking corrective actions is important.
• Performance and status of remote sites are tracked, and faults are addressed.

Bandwidth Management

• Bandwidth management is important due to the high cost of satellite bandwidth.
• Ku Band VSAT networks use shared bandwidth principles.
• Priorities and grouping of traffic can be defined.
• A high-priority group receives precedence in bandwidth allocation over a lower-priority group.

Miscellaneous Considerations

• VSAT equipment performance at both hub and remote earth stations is affected by ambient conditions.
• Hub equipment generates a lot of heat, so continuous heat dissipation and maintaining normal temperature is important.
• Important items for proper functioning of Remote Earth Stations include:
• Maintaining room temperature
• Using online UPS
• Good quality earthing
• Dust-free environment
• Sufficient air circulation
• Proper switch-on sequence
• Reporting any equipment problems to the hub
• Using the computer only for intended applications
• Ensuring computers are virus-free
• Logging equipment failures and engineer visits
• Allowing only authorized and trained personnel to operate the system
• Precautions:
• Do not switch on the VSAT immediately after switching off
• Do not move the indoor unit after installation
• Do not keep anything on the indoor unit
• Do not block air vents
• Do not use a water-based air cooler
• Do not bend the IFL cable
• Do not use the PC for other applications
• Do not attempt local servicing
• Do not move equipment without trained personnel
• Do not load unauthorized software