Satellite Communication System PDF

CHAPTER XXII SATELLITE COMMUNICATION SYSTEM 22.1 Very Small Aperture Terminal (VSAT) Network 22.1.1 Introduction VSAT provides Point to Point or Point to Multi Point data connectivity using Geost...

CHAPTER XXII SATELLITE COMMUNICATION SYSTEM 22.1 Very Small Aperture Terminal (VSAT) Network 22.1.1 Introduction VSAT provides Point to Point or Point to Multi Point data connectivity using Geostationary Satellite as repeater location. As satellite is being used as repeating stations, the data originating and terminating point can be anywhere on the earth. VSAT network in Indian Railways is typically used for UTS/PRS & FOIS connectivity and as Accident Site Communication for voice, data and video transmission. Railway is using them to provide connectivity between various Railway data networks and remote locations where the normal data connectivity is not available or provision of the same is not feasible. 22.1.2 IR VSAT Network Components a) The Indian Railway VSAT network works in a Star architecture and consists of i. Hub Earth Station ii. Remote Earth Station iii. Satellite Transponder & Space Link iv. Network Control Centre v. Interface Equipment b) The IR VSAT network provides transparent transmission links that can work with any network using suitable Interface equipment. c) IR Satellite network operates in Ku Band and operates on up link frequency of 13.75 to 14.5 GHz and down link Frequency of 10.70 to 12.75 GHz. Uplink frequency is the carrier frequency on which Hub or remote earth station transmits the Signal to Satellite. Down Link Frequency is the Carrier frequency on which Satellite transmits the Signal to Hub or remote earth station. 22.2 Hub Earth Station 22.2.1 IR’s present HUB Earth station is situated at New Delhi station. It is the Heart of the entire Network. The communication between remotes or remote to external networks is established through Hub Earth Station only. It is responsible for collecting the data from enterprise LANs, Address Translation, converting data into IF and RF Signals and transmitting them to Satellite and further to remote earth stations/terminals, maintaining the integrity checks for all remote earth stations, time synchronization for all remote earth stations, tracking of Satellite, converting the RF received from Remote to Data Signals in appropriate format to be delivered at Enterprise level etc. The NDLS Satellite Hub has now been upgraded to the latest HX Satellite technology. Indian Railways Telecom Manual - 2021 Page 309  SALIENT FEATURES OF HX NETWORK A. Network Efficiency: The new configuration will be able to provide 12Mbps of out-route and 7.4Mbps in-route from currently 6.5Mbps & 5.1Mbps respectively, hence Indian railways will get 65% more bandwidth in the existing transponder space. B. Bandwidth: Large bandwidth pool availability for all the users after going on a single network. C. Troubleshooting: Single window troubleshooting. D. Mobility solution: HX platform is having capability to support mobility applications. HX 200 modem used in A-route ART VSAT system is capable of collecting Lat Long parameters automatically through GPS, this facility was not available in old HN network equipment. E. Advanced Technology: HX network works over DVB-S2 technology with Adaptive Coding Modulation (ACM), the world’s most successful satellite industry standard. F. AIS: Adaptive Inroute Selection (AIS) for maximum bandwidth efficiency. G. QoS: Service level control providing the ability to have multi- level QoS offerings. H. Flexibility in configuration: Flexible configurations with multiple networking topologies: star, mesh, and multi-mesh. I. CIR: Each remote link can be independently configured with unique Committed Information Rates (CIRs). J. Capability: Able to work over 02 different transponders on the same satellite for a single network. 22.2.2 The transmission of a signal up to the satellite and back down is called a hop. Transmission delay for one hop is between 240msec. and 270msec. 22.2.3 Railway has hired 12 Mhz frequency space on GSAT 18 for their VSAT Network. 22.2.4 To adjudge the availability of Satellite communication, a link budget calculation is done taking the least available Satellite Power, Antenna Size, transponder sizing for receive and transmit segments etc. 22.2.5 All transponder space is allocated by the Department of Space. 22.3 Remote Earth Station 22.3.1 Remote Earth Station consists of i) A Parabolic Antenna ii) An outdoor unit called ODU, which has a Block Up Converter (BUC) to transmit and Low Noise Block (LNB) to receive signal. iii) Indoor Unit iv) Power Supply Arrangements v) Protection and Earthing Arrangements Indian Railways Telecom Manual - 2021 Page 310 22.3.2 Indoor Unit interacts with the Antenna System as well as external data devices through Ethernet LAN ports. A typical remote earth installation over Railway has been shown in Annexure-4. 22.3.3 All remote installations require feeding of latitude and longitude information which determines its location with respect to Satellite as well as Hub Earth Station along with some other hub related parameters to make remote sites live in the network. 22.4 Interface Equipment 22.4.1 The VSAT Network is interfaced with the external data devices by using Router or Router Switch combinations at Hub Earth Stations. At Remote Station, Ethernet LAN output is provided as standard interface. This can directly be connected to any device having Ethernet interface. 22.4.2 The applications Servers like FOIS Server of Railway, IP Exchange for Voice Networks and MPEG Server for Video Streaming applications and Web Servers for providing Internet application have to be interfaced with VSAT network through a router switch combination only. 22.5 Network Control Center 22.5.1 Network Control Center is responsible for administering and managing the whole of the VSAT Network as well as each of the applications working on the Network. This is carried out through Network Management System specific to Network as well as using other tools mostly SNMP based. 22.5.2 This Center also generates various analysis reports for Network part for day to day operation. 22.5.3 One of the most important parameters is analyzing the traffic flow and taking corrective actions for optimum working of all applications. This has been described in detail in Bandwidth Management para. 22.5.4 This Center also tracks the performance/status of all the remote sites connected and get them attended in case of any fault. 22.6 Bandwidth Management 22.6.1 Management of Bandwidth is a very important parameter on VSAT networks as the cost of Bandwidth on Satellite is very high. 22.6.2 Ku Band VSAT Networks work on Shared bandwidth principles. Here only priorities and grouping of traffic can be defined. Priorities can be defined for a group consisting of Data Transmitting device, Data Receiving Device etc. within the group each member will have an equal right for the bandwidth. Therefore as more and more members of the Indian Railways Telecom Manual - 2021 Page 311  group become active, each one will get less bandwidth. As more and more members become dormant, the available bandwidth for the remaining members will be higher. Priorities can be set for different groups based on sensitivity of applications. Therefore a high priority group will get precedence for bandwidth allocation than a lower priority group. This results in a very effective utilization of Bandwidth. 22.7 Miscellaneous 22.7.1 The performance of VSAT equipment both at Hub Earth Station and Remote Earth Station is affected by ambient conditions. 22.7.2 Hub Equipment generates a very high amount of heat. Continuous heat dissipation and marinating Normal temperature is an extremely important consideration for proper functioning of VSAT Hub Equipment. 22.7.3 Some of the important items which are considered necessary for proper functioning of Remote Earth Station are as given below i) Maintain the Room Temperature. ii) Use On line UPS. iii) Very Good Quality Earthing to be maintained. iv) Dust free environment to be maintained. v) Sufficient air circulation & access to Indoor Unit be there. vi) Switch on the VSAT first and then switch on other accessories. vii) Follow the Switch on Sequence strictly. viii) Report any Problem related to any equipment to Hub. ix) While doing so report full Problems and complete observations to Hub. x) Use the Computer only for Intended applications. xi) Make Sure your Computers are Virus FREE. xii) Log all activities related to equipment failures & Engineer visits in a Log Book. xiii) Allow authorized and Trained People only to operate the system. xiv) Do not switch on the VSAT immediately after switching off. xv) Do not Move the Indoor Unit after installation. xvi) Do not keep any article on Indoor Unit. xvii) Do not obstruct the air vents in front of the Indoor Unit. xviii) Do not use an air cooler (water) for cooling. xix) Do not Bend IFL cable. xx) Do not use the PC for any other application. xxi) Do not do any local servicing of the equipment. xxii) Do not shift the equipment from one place to another in absence of trained persons. xxiii) Do not load any software programs on the PC except the application. Indian Railways Telecom Manual - 2021 Page 312  Annexure-1 Indian Railways Telecom Manual - 2021 Page 313  Annexure-2 Indian Railways Telecom Manual - 2021 Page 314  Annexure-3 Indian Railways Telecom Manual - 2021 Page 315  Annexure-4 Indian Railways Telecom Manual - 2021 Page 316  Annexure-5 Remote Indoor Unit HX90 Platform - Inbound HIS 512Kbps /1Mbps - MPLS QoS - DHCP server and relay support - IGMPv2 for multicast to LAN - VLAN Tagging - ICMP support (pings, etc.) - Embedded web server for remote status query and configuration - NAT/PAT - RIP V1/RIPv2/BGP - DNS caching and preload - VRRP - Dynamic coding ACM/AIS - CLTC and CLPC - CBR/CIR/BE - Static and Dynamic Addressing - Inroute IP header compression - RTP header compression - PEP and inroute prioritization - PEP and TCP payload compression - Secondary satellite frequency support - CBR support for real-time applications - VADB -x-x-x- Indian Railways Telecom Manual - 2021 Page 317