Frequently
Asked Questions
1.
What does VSAT stand for?
VSAT stands for Very Small Aperture Terminal
2.
What is a VSAT?
VSATs are small earth stations (normally 1.4 - 2.4 meters)
that are utilized for reliable transmission of data, voice and
fax via satellite. VSAT Terminal Equipment consists of two
units - an indoor unit and an outdoor unit.
The outdoor unit is placed outdoors for a line-of-sight to the
satellite and the indoor unit interfaces with the user's
communications device (e.g. data terminal equipment). The
outdoor unit consists of a small antenna, mount and
electronics for signal reception and transmission. The indoor
unit consists of a satellite modem and demodulator(s) and a
network access device to interface with data LANs and PBXs.
3.
For what are VSATs used?
VSAT systems generally connect a large number of
geographically dispersed sites to a central location. VSAT
networks may transmit voice, data, fax, or video conferencing.
4.
What are the components in a VSAT site?
A typical VSAT site consists of a parabolic-shaped antenna
mounted on the roof of a building, connected by a cable to a
chassis inside the building. Operators install these antennas
at customer sites and buy transmission capacity on satellites.
5.
What does the VSAT unit contain?
A typical VSAT unit contains a modem for translating satellite
transmissions back into data (and vice versa) and terrestrial
interfaces for connecting customer equipment.
6.
What is a satellite transponder?
A satellite transponder is a combination receiver, frequency
converter, and transmitter package. It is physically part of a
communications satellite. Communications satellites typically
have 12 to 24 onboard transponders.
7.
What are the typical VSAT network configurations?
VSAT networks can be arranged in point to point, star, mesh,
star/mesh, and broadcast configurations. The preferred
arrangement depends on the kind of information flow the
network will service. <Top>
8.
What is a point to point VSAT network?
A point to point network allows two-way communications between
two VSAT sites. <Top>
9.
What is a star VSAT network?
A star network allows any number of VSAT sites to have two-way
communication with a central hub. <Top>
10.What
is a mesh VSAT network?
A mesh network allows two-way communications between any VSAT
sites in a network. A central hub is not necessary. Each site
communicates to another site with a single satellite hop. <Top>
11.What
are the different VSAT transmission methods?
There are three basic VSAT transmission types: TDMA,
time-division multiple access; DAMA, demand-assigned multiple
access; and SPCP/MCPC, single/multiple channels per carrier. <Top>
12.What
are the characteristics of a TDMA transmissions type?
TDMA is a form of multiple access in which a single carrier is
shared by many users. When signals from earth stations reach
the satellite, they are processed in time segments without
overlapping. TDMA is typically used in a packet switched
environment when small or moderate amounts of data are to be
transferred. <Top>
13.What
are the characteristics of a DAMA transmission type?
The DAMA protocol is used to share bandwidth in a time
division mode. Typically DAMA transmission is used in a
packet-switched environment when large amounts of data are to
be transferred. Is a highly efficient means of instantaneously
assigning telephony channels in a transponder according to
immediate traffic demands. DAMA is also applicable in a
circuit-switched environment and is usually characterized by
allowing each user a variable slot of time on a demand (or
request) basis. <Top>
14.What
are the characteristics of a SCPC/MCPC transmission type?
SCPC/MCPC systems use a dedicated satellite link between a few
distinct locations. These links can support either a single
telephone line or several telephone or data lines. Such links
generally are permanently assigned with no carrier switching
or rerouting over the satellite. <Top>
15.What
is SCPC-DAMA transmission?
SCPC/DAMA systems provide a control network on top of an SCPC
network. When a particular station wishes to make a telephone
call, the control network is used to forward that request to a
central processor that sets up a dedicated SCPC link between
the two sites. When the call is finished, the link is taken
down and the satellite resources can be used for a different
call. <Top>
16.
What is TDM-TDMA transmission?
TDM-TDMA networks are designed for interactive data
applications. TDM-TDMA systems feature a large expensive hub
that provides basic data communications to very inexpensive
remote sites. The architecture supports many remote stations
using a small amount of satellite bandwidth. Data rates
supported at the remote sites are typically between 1.2 kbps
and 9.6 kbps; however, this type of traffic has a very low
average data rate. Each station may transmit bursts of 9.6
kbps data, but they generally average less than 100 kbps.
Typical applications are transactional in nature. Examples
include credit card verifications, point of sale systems,
SCADA systems, and inventory control.<Top>
17.
What is TDMA-DAMA transmission?
TDMA-DAMA networks have the same demand assignment capability
as SCPC-DAMA networks, but also have division multiplexing to
reduce the need for multiple modems at each site. TDMA-DAMA
networks allow many telephone calls to be placed
simultaneously to different destinations through a single
station. <Top>
18.
What is FDMA transmission?
FDMA (Frequency Division Multiple Access) uses a single modem
for all communication from a site and transmits for very short
interval and at higher rates. FDMA uses multiple carriers
within the same transponder within which each uplink has been
assigned frequency slot and bandwidth. It is usually used in
conjunction with frequency modulation. <Top>
19.
What is the advantage of a TDMA-DAMA system?
TDMA-DAMA systems support many telephone lines with very
little incremental cost. E1 or T1 interfaces can be provided
for direct digital connections to PBXs or telephony switches.
TDMA-DAMA systems are also flexible in supporting applications
such as data, video conferencing, broadcast, and the like. In
addition, TDMA networks are hubless, which eliminates the high
cost of a hub and a single point of failure within the
network. <Top>
20.
What applications do TDMA-DAMA networks best support?
TDMA-DAMA networks support applications with mesh connectivity
and applications that require multiple services that are
integrated into a single network such as telephony, low to
high-speed data imaging, fax, and interactive video
conferencing. <Top>
21.
What are the advantages of VSAT?
1. A VSAT Network can be
provided through a lease arrangement with fixed transmission
costs regardless of distance. This provides for substantial
communication cost savings. The user retains complete control
of the way information is communicated within the network.
2. This generates flexibility,
particularly where new VSAT sites need to be added, or
existing sites need to be moved or removed from the network.
3. High availability and
excellent transmission quality is provided by the VSAT
Network.
4. VSAT Networks also guarantee
the highest performance levels (99.5%) among all communication
alternatives.
5. VSAT Networks provide fast
data transmission for POS applications to improve customer
service.
6. VSATs can be installed
anywhere the business has a site irrespective of the
terrestrial communications infrastructure.
7. VSAT Networks offer - a
single vendor for equipment service, installation &
maintenance of the entire network.
8. VSAT Networks offer superior
flexibility and performance. Adding a site is quick and easy,
and higher network availability levels are easy to obtain.
9. VSAT as a broadcast medium
supports business objectives to improve customer service and
quality. Reliable data broadcast, audio broadcast for in-site
music and video broadcast for sales training are all available
on a single platform.
10. Prices of VSAT Networks
compete favourably against terrestrial alternatives including
dial-up. The costs are predictable and stable.
11. VSAT Networks can be
secured with VPNs (Virtual Private Networks) using industrial
strength encryption <Top>
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