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What is VSAT?

02 Jul

sumber: http://www.tech-faq.com

VSAT is an abbreviation for a Very Small Aperture Terminal. It is basically a two-way satellite ground station with a less than 3 meters tall (most of them are about 0.75 m to 1.2 m tall) dish antenna stationed. The transmission rates of VSATs are usually from very low and up to 4 Mbit/s. These VSATs’ primary job is accessing the satellites in the geosynchronous orbit and relaying data from terminals in earth to other terminals and hubs. They will often transmit narrowband data, such as the transactions of credit cards, polling, RFID (radio frequency identification) data, and SCADA (Supervisory Control and Data Acquisition), or broadband data, such as satellite Internet, VoIP, and videos. However, the VSAT technology is also used for various types of communications.

Equatorial Communications first used the spread spectrum technology to commercialize the VSATs, which were at the time C band (6 GHz) receive only systems. This commercialization led to over 30,000 sales of the 60 cm antenna systems in the early 1980s. Equatorial Communications sold about 10,000 more units from 1984 to 1985 by developing a C band (4 and 6 GHz) two way system with 1 m x 0.5 m dimensions.

In 1985, the current world’s most used VSATs, the Ku band (12 to 14 GHz) was co-developed by Schlumberger Oilfield Research and Hughes Aerospace. It is primarily used to provide portable network connection for exploration units, particularly doing oil field drilling.

Implementations of VSAT

Currently, the largest VSAT network consists of over 12,000 sites and is administered by Spacenet and MCI for the US Postal Service (USPS). Walgreens Pharmacy, Dollar General, CVS, Riteaid, Wal-Mart, Yum! Brands (such as Taco Bell, Pizza Hut, Long John Silver’s, and other fast food chains), GTEC, SGI, and Intralot also utilizes large VSAT networks. Many huge car corporations such as Ford and General Motors also utilizes the VSAT technology, such as transmitting and receiving sales figures and orders, along with announcing international communications, service bulletins, and for distance learning courses. An example of this is the “FordStar Network.”

Two way satellite Internet providers also use the VSAT technology. Companies like StarBand, WildBlue, and HughesNet in the United States and SatLynx, Bluestream, and Technologie Satelitarne in Europe, and many other broadband services around the world in rural areas where high speed Internet connections cannot be provided use it too. A statistic from December 2004 showed that over a million VSATs were in place.

VSAT Configurations

Most of the current VSAT networks use a topology:

  • Star topology: This topology uses a central uplink site (eg. Network operations center (NOC)), which transports the data to and from each of the VSAT terminals using satellites
  • Mesh topology: In this configuration, each VSAT terminal will relay data over to another terminal through the satellite, acting as a hub, which also minimizes the need for an uplink site
  • Star + Mesh topology: This combination can be achieved (as some VSAT networks do) by having multiple centralized uplink sites connected together in a multi-star topology which is in a bigger mesh topology. This topology does not cost so much in maintaining the network while also lessening the amount of data that needs to be relayed through one or more central uplink sites in the network.

VSAT’s Strengths

VSAT technology has many advantages, which is the reason why it is used so widely today. One is availability. The service can basically be deployed anywhere around the world. Also, the VSAT is diverse in that it offers a completely independent wireless link from the local infrastructure, which is a good backup for potential disasters. Its deployability is also quite amazing as the VSAT services can be setup in a matter of minutes. The strength and the speed of the VSAT connection being homogenous anywhere within the boundaries is also a big plus. Not to forget, the connection is quite secure as they are private layer-2 networks over the air. The pricing is also affordable, as the networks themselves do not have to pay a lot, as the broadcast download scheme (eg. DVB-S) allows them to serve the same content to thousands of locations at once without any additional costs. Last but not least, most of the VSAT systems today use onboard acceleration of protocols (eg. TCP, HTTP), which allows them to delivery high quality connections regardless of the latency.

VSAT Drawbacks

As with everything, VSAT also has its downsides. Firstly, because the VSAT technology utilizes the satellites in geosynchronous orbit, it takes a minimum latency of about 500 milliseconds every trip around. Therefore, it is not the ideal technology to use with protocols that require a constant back and forth transmission, such as online games. Also, surprisingly, the environment can play a role in slowing down the VSATs. Although not as bad as one way TV systems like DirecTV and DISH Network, the VSAT still can have a dim signal, as it still relies on the antenna size, the transmitter’s power, and the frequency band. Last but not least, although not that big of a concern, installation can be a problem as VSAT services require an outdoor antenna that has a clear view of the sky. An awkward roof, such as with skyscraper designs, can become problematic.

 
1 Komentar

Ditulis oleh pada 2 Juli 2008 in Telecommunication, VSAT

 

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One response to “What is VSAT?

  1. meyes

    15 Agustus 2008 at 12:20 pm

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