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- What is ALOHA?
ALOHA is a term used to describe a group
of protocols used for the radio data transmissions
in computer networks. This protocol enables
the communication between several (more than
two) stations, solving problems caused by the
simultaneous transmission from many stations,
by scheduling time slots to each station. There
are many variations of Aloha protocol. In a
satellite communication network we use so-called
two-dimensional Aloha protocol, which schedules
not only the time slot, but also the frequency
ranges in which a particular station can transmit.
It helps to increase the effectiveness of the
scheduled frequency band. The name of the protocol
comes from the Hawaiian word used for greetings;
the protocol was first designed in Hawaii to
ensure the communication between the islands
of archipelagos.
return to FAQ
- What is an offset antenna?
An offset antenna is a variation of the
parabolic antenna use for satellite communication.
In parabolic antennas the focusing cup plays
the role of a mirror concentrating a weak signal
from a distant satellite in antenna's focal
point where the receiver (and sometimes transmitter)
waveguide is placed. In offset antenna the focal
point is moved down in relation to its geometric
axis by a certain angle. "Towards satellite"
direction is moved up by the same angle. Consequently,
geometric axis of the cup is focused not on
the satellite by accordingly lower. Lower cup
angle means less possibility of snow and ice
residue. This ensures a better functioning antenna
in winter, minimizing the necessity for the
de-icing systems. DataTrans offset antennas
often appear as if they were set in the direction
below the horizon, when in fact, they are focused
on the satellite just above the horizon. The
use of offset antennas dramatically eliminates
the interruptions in a connection caused by
the icing of the antenna.
return to FAQ
- What does the „link budget" mean?
An adequate transmitter power is necessary to
ensure the satisfying reliability of a radio
connection. This power depends on many factors,
such as, distance, frequency, shape of the terrain,
the size, type and placement of the antenna,
the signal loss in the atmosphere and the demanded
level of the link accessibility. The link budget
is an equation showing the necessary power of
the transmitter (or antenna parameters) as a
function of all the remaining factors. A correctly
designed link must take into account all the
extreme weather conditions like clouds, rain
etc. The links employed by the DataTrans Company
have been designed with the expected accessibility
of no less than 99,5%
return to FAQ
- What does DAMA mean?
An indubitable perfect scenario would have
the satellite terminal user to constantly receive
its entire scheduled communication channel throughput.
However, such a solution in most cases leads
to a very low effectiveness of the scheduled
channel and therefore a very high price of the
solution. In reality though, a significant percent
of the channel bandwidth, can be shared by a
number of users. Terminals have to request the
access to the slice of shared radio channel
when they have a complete packet of data to
be sent. The method of allocation depends on
the operator. The purpose of DAMA (Demand Assigned
Multiple Access)- assigning access according
to one's needs, is to optimize the use of critical
media- the radio channel throughput
return to FAQ
- What has VSAT got in common with de-freezer
and what is "de-icing"?
With frequencies ranges of several tens
of GHz the propagation of radio waves takes
place practically along the straight line. These
waves reflect from metal surface like the light
reflects from the mirror. In order to gain connection
with a 40 thousand kilometers distant satellite
a beam has to be specifically formed and directed.
Should the snow and ice happen to cover the
reflector, they change its shape and affects
or even block the communication. The de-icing
system is an optionally used parabolic antenna
set to help to melt the remaining snow and ice.
In a Polish weather conditions de-icing is advised,
especially with high importance links. The DataTrans
network central communication node antenna is
equipped with de-icing system, while for other
antennas this system remains optional
return to FAQ
- What is Hub and what role does it play
in satellite communication?
Hub is a transmitting and receiving central
station, that is: a central node of a VSAT station
based satellite communication system. In this
system the transmission always leads through
the central node of the network and SAT stations
are connected and arranged in a "star"
type configuration. Also, the central management
system of the network is in most cases connected
with the hub.
There are also hub-less systems without one
central, dedicated station providing node-to-node
connection. However, even in this system one
of the stations remains central by being related
with the management system of the network. These
are the mesh systems.
In the SkyWAN network there is one central node
(in the suburbs of Warsaw) that manages and
controls all the VSATs network.
return to FAQ
- What is the Minister of Communication's
license necessary for?
License is a basic document entitling the
company to provide telecommunication services.
It specifies the number of services, the field
of activity as well as all general and specific
conditions limiting the range of activities
or imposes additional obligations such as eg.:
obtaining necessary permits, informing the authorities
about undertaken actions, bases for the controls
done by entitled authorities. License is granted
for specified period of time (15 years for the
DataTrans company).
return to FAQ
- What is the Geo-synchronous satellite?
A geo-synchronous satellite is an artificial
Earth satellite PLACED in so-called geosynchronous
orbit in the equatorial plane 37,600 km from
the equator. This orbit's main characteristic
is that any object placed on it moves synchronously
to Earth revolution regardless of its own weight
(Earth revolution time for such object is equal
to the astronomical day). Consequently, an antenna
fixed and pointed in its direction will always
be positioned in the correct direction.
DataTrans uses the Orion F1 Geo-synchronous
satellite placed on 37.5°
return to FAQ
- What does SCPC (Single Channel Per Carrier)
mean?
SCPC is a type of satellite link, closest
in its function to the dedicated access link.
Every link has got a particular intensity (carrier).
The SCPC link does not support sharing of the
transmission channel.
return to FAQ
- What is a satellite segment?
A connection via an artificial Earth satellite
means that the ground stations transmit to the
satellite, the satellite amplifies the signal
and retransmits it back to Earth (on different
frequency than it was received). The on-board
radio installation in the satellite may receive
transmission in a specified wide frequency band
and retransmit it in another band. This band
is shared among the users who purchase/rent
from the satellite's owner the right to use
its part. Antennas of all the ground equipment
are pointed in the direction of the satellite
and the radio installation transmit and receive
in an agreed frequency range. The user's telecommunication
equipments (local network nodes) are connected
to the satellite terminals (VSATs), whose job
is to ensure the information transmission to
the satellite and reception of the information
sent by the satellite.
A user can distinguish between a well organized
satellite communication and communication conducted
entirely by the ground systems, only by a slight
delay of the signal (appearing because of the
distance to the satellite and speed with which
radio waves travel)
A satellite segment is a set of equipment ensuring
the communication via satellite. Putting it
another way- it is this part of the network
that one does not have to be familiar with nor
aware of.
return to FAQ
- What is a satellite transponder?
A telecommunication satellite is simply
such kind of a transmitting space station as
the ones used to retransmit the TV program to
the distant part of the country.
It consists of both: transmitter and receiver
joined together. In order to prevent interference,
transmitting and receiving are done on different
frequencies and antennas are polarized in perpendicular
planes In order to simplify the global management
(and to minimize the possible losses in case
of a breakdown in space), instead of one pair
(receiver and transmitter), the satellites are
equipped many independent pairs. Each such pair
is called a transponder. Every transponder may
serve one or more customers.
return to FAQ
- What is a VSAT (Very Small Aperture Terminal)?
VSAT is a ground receiving and transmitting
station cooperating with the Geo-synchronous
satellite. Such station consists of two modules-
Out-Door Unit (ODU), a receiving and transmitting
unit assembled out-doors and integrated with
the parabolic antenna; and In-Door Unit (IDU)
an assembled in-door operating/control/managing
module supplied with the necessary interfaces.
A parabolic antenna diameter is of no more than
2,4m. In practice, the antenna diameter is calculated
based on the satellite link budget.. For the
SkyWAN.Transfer service the DataTrans Company
uses antennas with the diameter of 1,2m and
Gilat Satellite Networks manufactured IDU modules.
VSAT name emphasizes very small dimensions of
the antenna- typical for the satellite TV receivers.
Antennas used in the satellite communication
centers, where it is necessary to ensure much
higher throughputs are several times larger.
The similarity in shape and size of the VSAT
antenna and TV antenna is not accidental: in
order to lower the cost of the VSAT it was designed
with as many mass-produced, and therefore cheap
elements used in satellite TV receivers as possible.
In spite of their simplicity, VSATs have been
successfully used in a wide variety of professional
applications.
return to FAQ
- What does VSAT consist of?
VSAT is a small satellite terminal, which
serves as a telecommunication network node and
a modem linked with satellite radio communication
station. It usually consists of ODU- Outdoor
Unit- (on the roof, building wall, foundation)
and IDU- Indoor Unit- (user's rooms). ODU resembles
with its shape a satellite antenna, while IDU
is an esthetically looking box, the size of
the video recorder. IDU is supplied with several
(usually two or four) user ports.
return to FAQ
- -How is the VSAT installation conducted
at the site of the client?
The VSAT station installation comprises:
-Placing and positioning of the ODU (antenna
with receiver and transmitter sets)
- Installation of an aerial cable between IDU
and ODU,
- Installation of the electric power supply
-Configuration of the IDU (modem and network
node)
- Conducting the test on the installation correctness
together with communication centre operators
- Installing the system software and configuration
data in IDU.,
- Connecting the VSAT to the network
- Configuration of the VSAT ports as specified
by the contract. Usually this needs two visits
of the specialist at the site of the installation:
one for the site survey and one for the installation
itself.
return to FAQ
- What is a site survey?
A site survey is a first stage of the VSAT
installation and is conducted in order to:
- Verify whether the installation may be
conducted in the desired place and check
if all formalities have been fulfilled (permission
from the property owner regarding the rooms
and the roof)
- To negotiate the antenna and IDU location
as well as the cable distribution plan with
the property owner.
- Prepare a project of the cable distribution
and any individual supporting elements for
the antenna and IDU that may be necessary
- Specify materials and tools necessary
for the installation and estimate labor
time of the installation
- Once all the formalities and necessary
technical preparations (eg.: making and
individually designed fixtures for a custom
antenna) are done it is possible to conduct
the final installation (this operation usually
takes no more than one day). Once the VSAT
is operating and connected to the network,
the remaining standard configuration procedure
may be remote-operated from the network
control center.
return to FAQ
- Can the VSAT be installed in anywhere in
Poland?
Yes. Poland is completely within
the reach of ORION1 satellite. However, it does
not mean that VSAT may be installed on any roof,
the installation location has to fulfill specific
requirements. Every planned location has to
be verified individually.
return to FAQ
- Is the VSAT radiation harmful for people
and animals?
VSAT includes a radio transmitter
with a typical power of 500mW and frequency
10GHz, placed in the antenna. A power of an
average mobile phone, which we use very close
to our heads is 2…3 with the frequency
of 900Mhz or 1.8GHz. Because of highly focusing
of the radiation beam by parabolic antenna it
would not be wise to remain within the radiation
reach longer- this may theoretically be harmful
for the body organs of size parallel to the
length of the wave in the beam (30mm), as eyes
or testicles. Still it may be guaranteed that
long before any charm might have a chance to
appear, such a person would be chased away by
the network administrator, as the presence on
the antenna would block the communication.
return to FAQ
- May the weather conditions interfere the
satellite connection through VSAT?
Four extreme weather factors may
potentially cause interferences in the satellite
transmission: 1. Storms blowing off or changing
the orientation of the antenna. 2. Wet snow
or ice changing the shape of antenna cup. 3.
A cloud layer several kilometers thick causing
additional muffling of the radio waves beam
between VSAT and satellite. 4. Direct or close
thunder damage
There are technical ways of preventing against
the first two factors: extra heavy bases, aerodynamic
cup protectors, and electrical cup heaters.
An adequate prevention against thunders limits
that threat. The problem with clouds seems to
be the most difficult- even if it was possible
to increase temporarily the VSAT transmitter
power, it is not possible to increase the satellite
transmitter power on request. In order to remain
secured in such situations the power of satellite
and ground transmitter are calculated with necessary
margin.
return to FAQ
- What are the necessary criteria for a place
where the VSAT is to be installed?
For the ODU (Out Door Unit that is:
antenna, transmitter end amplifier, receiver
antenna amplifier) it is necessary to be set
on a solid base where it could be pressed with
100kg ballast or permanently fixed in some other
way. This location must also ensure a direct
satellite "visibility" (for DataTrans
network: azimuth ca 2400, elevation ca 100)
A typical location is a flat roof, other locations
(on the wall, on the chimney) may need additional
formal (resistance verification) and technical
(special fixing constructions) preparations.
IDU needs a dry place free from frost, dust
and turbulences, with electrical power supply
(220V, 50Hz) and free air circulation. The IDU
is usually fixed on the shelf on the wall, below
the ceiling or on a stand with other telecommunication
equipment. It must be possible to connect both
units with two aerial concentric cables as short
as possible (not longer than50 meters)
return to FAQ
- Is the exploitation of VSATS under the
supervision/jurisdiction of country control
authorities?
Yes. As a receiving and transmitting
device every VSAT requires an individual license
from the State Radio Agency who also remains
entitled to conduct controls of the equipment
as well as to give some orders to Users. DataTrans
claims for all required licenses (and pays all
the fees) in the name of its Customer. The company
also keeps all the issued documents. Also the
State Telecommunication and Post Inspection
supervises the work of DataTrans network as
a fireless telecommunication network.
return to FAQ
- How often does it happen in Poland that
a thick cloud layer significantly interferes
with the satellite communication of SkyWAN?
A dedicated team at our company constantly
monitors the network reliability. The global
interference of the network takes place when
a thick cloud layer remains above the network
connection center in Legionowo, near Warsaw.
The total network inaccessibility (because of
all possible reasons) does not exceed 0,5%.
Assuming the worst-case scenario where all the
above-mentioned brakes in the connections caused
by the weather conditions and the clouds appear
with common probability above every spot in
Poland, we may estimate that the total duration
of any satellite terminal inaccessibility should
not exceed 1%.
return to FAQ
- How often are the PAR controls and is it
similar to Internal Revenue control that they
search as long as they find something and then
punish severely?
PAR controls the owner and operator
of the transmitting-receiving equipment, not
the Customer- the user. Controls are not frequent.
Because interpretation of Communication Act
is much easier than tax regulations, the results
of a control are far less controversial.
return to FAQ
- Who does the VSAT belong to and is it necessary
to insure it?
According to the standard contract,
DataTrans remains the owner of the VSAT. The
customer leases the communication ports. The
customer who supplies the location for the VSAT
installation has to take all the necessary effort
so as to prevent the VSAT from damage or theft
and therefore the client should arrange the
insurance for the VSAT. DataTrans may agree
to insure the VSAT on additional cost.
return to FAQ
- How quick will the connection be restored
after the „act of God" (when something
got broken or damaged)?
The time necessary to repair a failure
depends on many factors. An operator on duty
in the communication center monitors all the
network activities, however it is impossible
for him to distinguish between a failure and
a VSAT being switched off by its User. That
is why a User suspecting a failure at the side
of DataTrans, after spotting a brake in the
connection, should contact the operator and
report the error. DataTrans has branch offices
on major cities in Poland that are supplied
with necessary equipment and employing qualified
specialists. From a technical point of view
it should be absolutely possible to repair a
failure within one working day. In case of different
equipment failures, the repair order depends
on what was agreed in the contract and on technical
possibilities. DataTrans guarantees the time
necessary to start the repair works .
return to FAQ
- May the VSAT become the target for the
Russian radar-seeking missile?
As in case of a serious out of tune
condition of the receiver onboard the Russian
missile from the nominal frequency. Unfortunately
this factor is beyond the control of DataTrans.
The possibility of such accident has been mathematically
estimated and it is much lower from the possibility
that the local children use the VSAT antenna
to play a "flying saucer" game.
return to FAQ
- May the Wizja TV or Cyfra+ digital television
decoders be able to receive our data?
From the technical aspect, there
is a similarity of same kind between VSAT and
digital television decoders and receivers. Satellite
communication systems though, are based on different
schemas and transmission speed. Moreover, the
methods used to code the data are different
than the ones of digital television. Not all
technical details of Wizja TV nor Canal+ are
familiar to us, still we have not received any
claims from our customers regarding their data
being received by television systems.
return to FAQ
- May the SkyWAN link be used for Internet
purposed in the „free time"?
Technically it is possible and if
the Client is interested we may consider a possibility
of dimensioning the link so as to ensure effective
receiving of the data from the Internet network.
return to FAQ
- What is a 'network for transaction purposes"
and how does it differ from the other networks?
Thanks to the connection of telecommunication
equipment presenting different values, complementing
one another, SkyWAN network is designed to provide
universal solutions. At this point, however
is assigned to specialize in transaction purposes
that is, to optimize the transmission of small,
rare information to a great number of terminals
with a minimum service costs. Sporadically it
may also support batch applications. A trade
name for a telecommunication service associated
with it is- Transfer.
One may easily imagine networks designed for
other purposes, like connecting a small number
of non-stop transmitting Users. For such options
we have prepared a Cargo service based on a
much more expensive type of VSAT terminal.
return to FAQ
- Transfer, Cargo- how does it differ from
the SkyWAN network?
SkyWAN is a registered trademark
of a satellite telecommunication network built
by the company DataTrans being its formal operator.
Transfer, Cargo are the names of services offered
by the SkyWAN network. These services are characterized
by various values. Transfer is planned for narrow-band
transaction purposes and is the main service
offered by the DataTrans Company. Cargo is wide-band
service designed to work in either star or/and
„hub-less, mesh" topology.
return to FAQ
- Is it possible to brake into SkyWAN?
Yes, although it is prohibited by the law
and technically difficult. Anyone is entitled
to build a station for his own purpose of receiving
the satellite signal. Still, in order to get
access to information enclosed in such signal.
even disregarding the legal implications, one
would have to have obtained all the necessary
specs of the communication satellite, frequencies
used by SkyWAN, modulation types, data encoding
and configuration parameters. DataTrans protects
these crucial details with utmost care, but
at the same time the customers are requested
to individually code all the data they deem
confidential.
return to FAQ
- May a satellite break down?
Yes, although in the history of the satellite
communication it is a very rare accident. Adequate
solutions and procedures eliminate or limit
its consequences. History shows that so far
all satellite failures were caused by the space
rocket launches. Thanks to redundant on-board
equipment, use of selected custom components
and unique production procedures, the telecommunication
satellite is more resilient to failures than
equivalent ground installations. However, should
a chain of failures cause a critical situation,
the fail over systems, such as, like the use
of backup satellites are available.
return to FAQ
- May the satellite be interrupted/interfered
with?
Commercially used VSAT stations are
subjects of special homologation procedures
conducted by satellite operators and are not
permitted to operate without necessary certificates.
These certificates are issued independently
of the telecommunication licenses granted by
the state authorities. Interrupting the satellite
on purpose is possible with the use of special
equipment but it may be easily spotted by operator
services. Such cases, because of their obvious
retaliatory character, are extremely rare and
considered military actions .
return to FAQ
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