Knowledgebase
Knowledgebase:
Understanding VSAT
Posted by Martin Kivuva, Last modified by Simon Njagi on 16 June 2011 12:35 PM
FAQS

What is VSAT ?
What is One-way Satellite ?
Who uses VSAT ?
What is a BUC?
What does LNB stand for?
What does OMT stand for?
What is LHCP and RHCP?
Can I use LinkStar to implement Voice over IP (VoIP)?
How do I connect a PC or a Local Area Network (LAN) to the LinkStar terminal?
I connect the LinkStar terminal to a wireless LAN (W-LAN) network?
Is Linux possible as primary Operating System?
Who can install the system?
Who provides support for LinkStar?
What is contention Ratio?
What is the full form of TDM/TDMA and SCPC?
How to check a computer's IP Address?
What is a gateway?
What is ping?
Are satellites unreliable?
What does "availability" actually mean?
What are the site requirements for a VSAT installation?
Why does the dish size affect the transmission price?
What is a point to point VSAT network?
What is a star VSAT network?
1.What is VSAT ?

VSAT stands for Very Small Aperture Terminal - its a catchy acronym and as such its been adopted by all and sundry for every type of satellite product from small components of a system to complete systems. Because the term really hinges around the small size of the antenna it has been used to describe both one-way and interactive systems. Typically, interactive Ku-band antenna sizes range from 75 centimetres to 1.8 metres. One way systems can use antennas as small as 45 centimetres.

2. What is One-way Satellite ?

One way systems rely on a transmitting station which transmits one or more carriers to the satellite which re-broadcasts the signal over its coverage area. All receive-only VSATs under the satellite footprint can then receive the signal or the user/operator is able to define groups of VSATs from one to all on the network. Broadcast systems are used for data and audio. The most popular application for data is the transmission of financial feeds - Reuters, Telerate and KnightRidder are good examples of companies with large data broadcasting networks - however, there are many other uses, such as software downloads, file transfers, transmission of press agency news items (with pictures) and the broadcast of paging messages for terrestrial transmission to the pagers themselves.

3. Who uses VSAT ?

You name it really, car dealerships, gas stations, lottery systems, banks, insurance companies, drug stores, general stores, supermarkets, healthcare companies, manufacturers, couriers, hotel chains, car rental businesses, food manufacturers, heavy industries, mines, electrical utilities, oil and gas pipelines, energy production and exploration, timber companies, plantations, various government departments and agencies ....... any others you can think of, just add to the list.

4.What is a BUC?

Block Up Converter, it up converts and amplifies modem information for transmission to the satellite.

5.What does LNB stand for?

Low Noise B lock down converter, it down converts and amplifies signals received from the satellite for transfer to a receiver

6.What does OMT stand for?

Ortho ( or orthogonal) Mode Transducer, this device separates and directs signals of two different polarities, i.e. Horizontal and Vertical or LHCP and RHCP

7.What is LHCP and RHCP?

They are orthogonal senses of circular polarization L eft H and or R ight H and Circular Polarization.

8.Can I use LinkStar to implement Voice over IP (VoIP)?

LinkStar offers the ability to implement VoIP. However, due to the long satellite path, there is an important round loop delay of typically 1.5 seconds. This needs a telephone conversation rather to be simplex, i.e. only one person speaks at a time. Nevertheless, VoIP based on LinkStar can be an attractive alternative in geographical regions with non-existing or poor telephone infrastructure.

9.How do I connect a PC or a Local Area Network (LAN) to the LinkStar terminal?

The indoor unit of the terminal provides a 10/100 Mps Ethernet Interface which allows you to directly connect a single computer (via a crossed Ethernet cable) as well as a network hub, switch, router or proxy server.

10.Can I connect the LinkStar terminal to a wireless LAN (W-LAN) network?

Yes, trough the Ethernet interface it is possible to connect directly a wireless access point or wireless bridge. No access PC or workstation is needed.

11.Is Linux possible as primary Operating System?

The LinkStar terminal is an independent station, with no PC needed for operation. Thus the operation system of the computers connected to the LAN is irrelevant, as long as it supports the Internet Protocol (IP). This is the case of all modern operating systems, including Linux and MAC OS.

12.Who can install the system?

The terminal has to be installed by a certified installer. Indeed special skills for installing and commissioning are needed, which go well beyond the installation of a satellite reception-only system.

13.Who provides support for LinkStar?

NSTT provides free e-mail and telephone support for all her LinkStar customers. If needed, exceptionally on-site support is offered at cost.

14.What is contention Ratio?

With most broadband technologies, some of the bandwidth is shared between other users. For example, if the service is contended or oversubscribed at 20:1, it means that you share the bandwidth with up to 19 other users.

15.What is the full form of TDM/TDMA and SCPC?

These are two different technologies used to build satellite networks. TDM / TDMA stands for Time Division Multiplexed / Time Division Multiple Access. SCPC stands for Single Channel Per Carrier.

16. How to check a computer's IP Address?

There are two ways to check the IP address of a PC:
I) Open MS-DOS window and use the following commands at DOS prompt
ipconfig (for computers running Windows NT) or
winipcfg (for computers with Windows 95,98)
It displays ip-address, subnet mask and gateway ip-address.

II) Right click on network neighborhood icon on your desktop and choose properties. Select the tcp/ip ethernet adapter of your PC, click on properties.

17. What is a gateway?

A gateway is a network point that acts as an entrance to another network. It is a link between two different networks. Gateway is configured under the tcp/ip setup window in network neighbourhood properties.

18. What is ping?
Ping is a basic Internet program that lets you verify whether a particular IP address exists and can accept requests. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating. Ping can also be used to see how long it takes to get a response back.
To use the ping command, go to the MS-DOS prompt and type:

ping

19. Are satellites unreliable?

No. Over the past 30 years, satellite technology has proven that it has very high service availabilities and low outages. They generally have better performance and availability than terrestrial circuits .

20.What does "availability" actually mean?


Space segment availability refers to the expected time that the Bit Error Rate will exceed that required, taking into account the predicted rain fade and performance of the receiver equipment in relation to the received signal.

21.What are the site requirements for a VSAT installation?

Dependent on site location within the satellite's footprint, a dish will normally be between 1.2m and 4.5m diameter and mounted on a flat roof. Suitable space and strength will be required to hold the dish and line of sight with the satellite is necessary. An external mains power source is required for the ORU. The Indoor Unit requires a stable mains power supply and suitable dry location. The customer will be fully advised to the exact requirements upon successful survey.

22.Why does the dish size affect the transmission price?


With a smaller dish the received power from the satellite is reduced, hence to provide the same service in terms of data speed, Bit Error Rate and Availability, the satellite power needs to be increased. This obviously has a direct effect on the cost of satellite capacity .

23. What is a point to point VSAT network?


A point to point network allows two-way communications between two VSAT sites.

24. What is a star VSAT network?


A star network allows any number of VSAT sites to have two-way communication with a central hub.




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