Frequently Asked Questions - What would
you like to know about VSAT systems?
- What do you mean by a 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. Specifically, we in the industry, isolate television broadcast receivers because
counting these as well would simply distort the numbers in the marketplace, but data,
audio and, to some extent, voice systems are included. Generally, these systems operate in
the Ku-band and C-band frequencies. As a rule of thumb C-band (which suffers less from
rain attenuation, but requires larger antennas) is used in Asia, Africa and Latin America
whilst Ku-band (which can use smaller antennas, but suffers from rain fade in a
monsoon-like downpour) is used in Europe and North America. Typically, interactive Ku-band
antenna sizes range from 75 centimetres to 1.8 metres and C-band from 1.8 metres to 2.4
metres. One way systems can use antennas as small as 45 centimetres.
- What about one-way systems?
- One-way or broadcast 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.
- So what is an interactive VSAT?
- Interactive VSAT systems come in two main network topologies - star and
mesh. The former tends to be based either on a shared access scheme (TDM/TDMA), which is
designed to support transactional processing applications, or on a dedicated link (the
satellite equivalent to a leased line). The latter usually uses links which are set-up and
torn-down on request to establish a direct link between two sites on a demand assigned
basis. These mesh systems were initially designed to support corporate and public network
telephony links, but are being increasingly used to serve high data rate services, such as
file downloads, at rates of 64 kbps or greater.
- This industry is full of acronyms - what do they mean?
- This gets complicated, but here is an extensive list of acronyms, terms, abbreviations and data rates for your reference. Like any other industry, it seems as though you will never
be able to understand, but its not that bad and it doesn't take long to get the basics.
- What about statistics?
- The VSAT market has been going since the early 1980s and the launch of
the first one-way VSAT system by Equatorial of California. Towards 1985 the first
interactive star systems began to be seen and it wasn't until 1989 that the first mesh
telephony products were really sold.
- What does a network look like?
- VSAT networks come in various shapes and sizes ranging from star data
system users with one site connected to an operator's shared hub to many thousands based
on a dedicated facility located at their own site. Mesh systems have traditionally been
somewhat smaller in size than star systems - 5 to 30 sites used to be a good rule of thumb
- but the average size of orders has risen as prices have come down and some rural
telephony networks now comprise as many as several hundred or even thousands of sites.
- What kind of companies use VSAT systems?
- You name it really, car dealerships, gas stations, 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.