| What
is rain fade?
What is a sun outage?
Are satellites unreliable?
What happens if a satellite does
fail?
What does "availability"
actually mean?
Is the service encrypted?
What are the site requirements
for a VSAT installation?
What is Landlords consent and
planning permission?
Does the dish move when in operation?
How far can the Indoor Unit be
installed from the satellite dish?
Why does the dish size
affect the transmission price?
What special on-site
equipment do I need?
Why does the VSAT antenna
size affect the price?
Who is responsible for the
remote site maintenance, Hub operation and connectivity of customer
data centres to the Hub?
What protocols and
physical interfaces are supported?
What are the remote
site requirements for a VSAT installation?
How far can the VSAT indoor
equipment be installed from the satellite dish?
What network management
facilities are available from a TDMA Hub?
What is the TDMA Hub used for?
What level of resilience
is offered at the TDMA Hub?
What is rain fade?
This occurs when there is
a significant rainfall, which can cause interference with the signal
due to an increase in noise. The service is designed to take this into
account.
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What is a sun outage?
A sun outage occurs during the solar equinox.
Throughout the year the sun moves over the Earth, reaching as far north
as the Tropic of Cancer (in June) and as far south as the Tropic of
Capricorn (in December). At the central point, as the sun moves across
the equator (in March and October), it can pass directly behind a satellite.
This causes a degree of interference due to an increase in thermal noise.
However, this only lasts a minute or so and is fully predictable both
in severity and duration.
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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.
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What happens if a satellite does fail?
The capacity used by BT for SatStar Africa is
non pre-emptible and fully restorable. This means that if the transponder
should fail, an alternative will be provided on the same satellite.
Should the satellite fail, the service will be relocated to an alternative
satellite where possible.
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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.
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Is the service encrypted?
Not as standard. Should encryption be required,
it is recommended that this be carried out at source, prior to transmission.
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What are the site requirements for a VSAT installation?
Dependent on site location within the satellite's
footprint, a dish will normally be between 1.8m 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.
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What is Landlords consent and planning permission?
Prior to the installation taking place the customer
will need to obtain permission from the Landlord and also from the local
planning authority for the installation.
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Does the dish move when in operation?
Once the dish has been aligned for service it
will not be moved.
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How far can the Indoor Unit be installed from
the satellite dish?
BT will provide 150m cabling between the dish
and the indoor equipment as standard. Additional cabling can be provided,
although this will incur an additional cost.
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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.
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What special on-site equipment do I need?
On site equipment will consist of an antenna,
LNB and satellite data receiver.
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Why does the VSAT antenna size affect the price?
With a smaller VSAT antenna 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.
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Who is responsible for the remote site maintenance,
Hub operation and connectivity of customer data centres to the Hub?
Normally BT is wholly responsible for the complete
connectivity chain, from the source of the data to its destination.
The entire link is fully managed by BT 24-hours a day 365 days a year.
The network management facilities are powerful and therefore many service
issues are flagged by the system automatically. The operations team
are able to diagnose issues at the customer remote sites using the network
management facilities and therefore a customer visit is often not required.
Should a visit be necessary however, then the closest engineer to the
customer site will be dispatched.
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What protocols and physical interfaces are
supported?
Typically, the following protocols are supported:
X.25
SDLC
IP Routing
X.3
X.28
BSC-327X.
The following physical interfaces are supported:
Serial RS232
10 base 5
AUI
10 base 2
10 base T.
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What are the remote site requirements for a
VSAT installation?
Dependent on network configuration and site
location within the satellite's footprint, a dish will normally be 1.8m
in diameter. Either a flat roof with space and strength to hold a 1.8m
dish or a ground mount will be required. If this is not available a
vertical wall strong enough to mount a bracket holding the dish will
be required. In both cases line of sight with the satellite is necessary.
The indoor equipment
requires a stable mains power supply and suitable dry location.
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How far can the VSAT indoor equipment be installed
from the satellite dish?
The dish must be placed within 100m of the indoor
equipment. A single cable links the two units; BT provides 30m cable
length as standard.
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What network management facilities are available
from a TDMA Hub?
Full management of the remote site components,
the data traffic flow to and from the remote sites, the routing of traffic
between the host and the Hub and statistical information concerning
data flows throughout the network.
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What is the TDMA Hub used for?
The Hub acts as the central focus of the network
providing all the control, routing network management and statistics
functions.
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What level of resilience is offered at the
TDMA Hub?
All equipment at the Hub site is installed in
a redundant mode with automatic backup onto the spare equipment. Power
is provided by an Uninterruptable Power Supply (UPS) with a generator
set to provide backup power.
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How Satellites Work
| Networks | Operational
Considerations | Equipment
Installation Procedures
| Internet over satellite | Glossary
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