Technology Options
Very small aperture terminals (VSATs) are used for both one-way and two-way
interactive systems. VSATs operate in India on the INSAT series of satellite on
the extended C-band. Then the government allowed the use of Ku-band. C-band,
which suffers less from rain attenuation, but requires larger antennae, is used
in Asia, Africa and Latin America, while Ku-band, which can use smaller
antennae, but suffers from rain fade in a monsoon-like downpour, is used in
Europe and North America and Asia. Typically, the size of an interactive Ku-band
antenna ranges from 75 cm to 1.8 meter and that of C-band ranges from 1.8 meter
to 2.4 meter. One-way systems can use antenna as small as 45 cm.
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A VSAT system consists of a satellite transponder, central hub or a master
earth station, and remote VSATs. A VSAT terminal installed at geographically
dispersed locations has the capability to receive as well as transmit signals
via the satellite to other VSATs in the network. Depending on the access
technology used, signals are either sent via the satellite to a central hub, or
directly to VSATs, with the hub being used for monitoring and control.
A VSAT comprises two units–outdoor and indoor. The outdoor unit consists of
an antenna and radio frequency transceiver (RFT). The antenna is typically 1.8
meter or 2.4 meter in diameter, though smaller antennae are also in use. The
indoor unit functions as a modem and interfaces with end-user equipment like
stand-alone PCs, LANs, telephones or EPABXs.
n One-way
Systems: A one-way VSAT system relies on a transmitting station that
transmits one or more carriers to the satellite that rebroadcasts the signal
over its coverage area. All receive-only VSATs under the satellite footprint can
then receive the signal or the user/operator can define groups of VSATs from
one-to-all on the network.
n Interactive
Systems: Interactive VSAT systems come in two main network topologies–star
and mesh. The star topology is based either on a shared access scheme (TDM/TDMA),
which is designed to support transaction-processing applications, or on a
dedicated link (the satellite being equivalent to a leased line). The mesh
topology usually uses links that are set up and torn down on request, to
establish a direct link between the two sites on a demand assigned basis. 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 higher.
n TDMA
and DAMA: The two alternatives for VSATs are: time designed multiple access
(TDMA) and demand assigned multiple access (DAMA). In a TDMA network, all remote
VSATs communicate with the service provider’s central hub station. The hub
station monitors and controls all VSATs in the network and the entire customer
traffic is routed through it. On the other hand, in the DAMA network, VSATs are
pre-allocated a designated frequency. Equivalent of the terrestrial leased-line
solutions, DAMA solutions use the satellite resources constantly. Consequently,
there is no call-up delay, which makes them most suited for interactive data
applications or high-traffic volume.
n Single
Channel per Carrier (SCPC): This refers to the usage of a single satellite
carrier for carrying a single channel of user traffic. In case of ‘SCPC VSATs’,
the frequency is allocated on a preassigned basis. DAMA network uses a pool of
satellite channels, which are available for use by any station in that network.
On demand, a pair of available channels is assigned, such that a call can be
established. Once the call is completed, channels are returned to the pool for
being assigned to another call. Since the satellite resource is used only in
proportion to the active circuits and their holding times, it is ideally suited
for voice traffic and data traffic in batch mode.
Top VSAT Service Providers |
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Rank* | Service Providers |
VSAT Base (31st Mar ’02) |
VSAT Base (3rd Mar ’01) |
VSAT Installed (in 2001-02) |
Mkt Share (in percent) |
1 | HCL Comnet | 2,051 | 1,218 | 833 | 50.82 |
2 | Comsat Max | 1,998 | 1,537 | 461 | 28.12 |
3 | HECL | 2,700 | 2,378 | 322 | 19.64 |
4 | Bharti Broadband |
638 | 440 | 198 | 12.08 |
5 | Essel Shyam | 230 | 140 | 90 | 5.49 |
6 | GNFC | 20 | 0 | 20 | 1.22 |
7 | RPG | 100 | 140 | -40 | -2.44 |
8 | HFCL | 70 | 121 | -51 | -3.11 |
9 | ITI | 45 | 128 | -83 | -5.06 |
10 | Telstra V-Comm | 210 | 321 | -111 | -6.77 |
Total | Â | 8,062 | 6,423 | 1,639 | 99.99 |
*Ranking based on number of VSAT installed in FY 2001-02 on the shared hub front |
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V&D Estimates |
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Buying Tips
Before buying VSATs, an enterprise has to decide upon the network size, the
type of network (dedicated or shared), network architecture (star or mesh),
technology (TDMA or DAMA), and the spectrum band (extended C-band or Ku-band).
n Network
Size: The buyer has to first decide upon the total number of sites that will
be covered by a VSAT, the number of users per site, and the range of
applications to be used. He will also have to ascertain the duration of usage by
different applications and users. The various applications can be voice, fax,
interactive data messaging, data broadcasting and data collection requirements,
and can vary from corporate to corporate. Corporates will also have to specify
the type of equipment (EPABX, telephone or LAN) to be connected to the VSAT, and
the physical interfaces and protocols to be used for the interconnection.
n Type
of Network: The corporate has to decide whether he wants a dedicated or a
shared hub network. In a dedicated hub scenario, the hub infrastructure is
utilized by a single corporate entity with all the VSATs in the network sharing
the available resources. Such a hub is recommended only when the number of sites is large and the application is
specific to the corporate. Unless the number of terminals are in the range of
300—350, it makes little economic sense to invest in a separate hub and
operate as a private captive network. Typical users of such hubs are banks and
stock exchanges.
In the case of shared hub, corporates share the hub along
with the other service providers. The shared hub service providers also handle
licensing and frequency coordination services. The advantage here is that users
can concentrate on their business areas instead of creating expertise and skills
in satellite communication systems, for effective utilization of the network.
n Network
Architecture: The two types of network architecture in use are star and
mesh. Star is the most commonly used architecture and uses VSATs and central hub
stations. This architecture works for both point-to-multi-point and
multi-point-to-point communication services. However, since the complete
communication has to switch through the central hub station, the link uses
double-hop satellite links, and hence, there is a delay of 540 ms. While this is
acceptable for many data applications, it is not preferred for real-time voice
and video-conferencing applications.
The mesh network uses identical-size VSATs for communication,
directly through the satellite. Thus, it needs large antennae. Since single hop
link is involved, this network is widely used for voice and video-conferencing
applications. These networks can be configured on demand assigned basis.
n Technology
Type: The corporate also has to decide whether it needs TDM/TDMA or the SCPC/DAMA
technology. In the DAMA technology, VSATs are pre-allocated a designated
frequency and it is quite similar to the terrestrial leased line. DAMA is ideal
for voice because there is minimum delay, whereas TDM/TDMA is ideal for data
applications.
n Spectrum:
The buyer has to state which band to opt for. Satellite communication
evolved exploring C-band and extended C-band, but Ku-band has been found to be
more appropriate for VSAT networks. However, this band suffers from some
attenuation during rain. Tropical countries like India prefer to exploit
extended C-band before using Ku-band, as it is not severely affected by rain.
Satellite transponders in extended C-band possess a bandwidth of 36 MHz, whereas
Ku-band has a bandwidth of 36/54/72 or 77 MHz.
After selecting the above elements, the corporate buyer has
to evaluate the type of VSAT that it plans to buy, the VSAT vendor, and the
service provider.
n Speed:
At present, the return speed varies from vendor to vendor and also from
product to product. One can get speeds varying from 156 kbps to around 1.2 Mbps.
So depending on the application and usage requirement, one can choose a
particular product, based on a particular technology.
n Throughput:
It specifies the end-to-end bandwidth that an enterprise gets and this is
where technology plays its role. A few vendors have been talking about bandwidth
conservation technologies like TCP/IP spoofing while others have been talking
about PCMA/CRMA.
n Technology:
As of now, there are four technologies in use. These are TDM/TDMA, FTDMA,
MFTDMA, and CRMA. Vendors are also moving from proprietary standards to open
standards, which is good for the corporate customer in the long run, as he will
have the option to hop from one service provider to another, depending on the
quality-of-service provided by different service providers. The open standard
that everybody has been talking about is DVB RCS.
n Cost:
The hardware cost varies, depending on the configuration that one goes for.
Apart from the hardware costs, bandwidth charges too form an important
component. Bandwidth costs can be negotiated depending on the number of VSATs
installed, and this approach can prove to be cheaper than the per kbps option.
The annual maintenance cost for the network is roughly around 6-8 percent of the
hardware cost.
n Quality
of Service (QoS): The user needs to aim for certain QoS demands for his
applications to run smoothly. For voice quality, mean opinion score (MOS) level,
blocking rate and bit error rate (BER) are specified. Interactive data services
require tolerable response time. Network availability is one of the major QoS
needs of the user.
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n Selection
of Service Provider: When the user opts for shared hub services, it is very
important to select the right service provider who can meet all his
requirements. The failure rate of remote VSAT equipment depends on the product,
while performance quality depends on the technology, the product and the network
architecture. End-to-end service to users and the overall network availability
is the sole responsibility of the service provider. In an infrastructure
project, such as a VSAT network, buyers can not easily shift from one service
provider to another, since the technology platform is proprietary. Hence, one
has to carefully evaluate the above criterion while choosing a VSAT service
provider. Customer services can vary widely from vendor to vendor. An effective
project management system and process adopted by the vendor will ensure
on-schedule delivery of VSATs and networks. A service provider must provider
comprehensive end-to-end services for onsite technical support, integration of
VSATs with user terminals, network applications and integration ability, and
process and infrastructure for delivering consistent service, optimum
utilization of the network. Also, round-the-clock helpdesk service, training of
corporate users, provision of transparent billing and service-level agreements,
ongoing service reports and review procedures, support during crisis,
demonstration of performance quality on demand, and assistance to network
augmentation when needed, will be required by the user.
Market Information
Market
Information
Top TDMA Vendors |
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Rank | Vendors | TDMA | Mkt Share |
1 | Gilat | 6,700 | 69.17 |
2 | Hughes | 2,772 | 29 |
3 | Viasat | 200 | 2 |
4 | ND Satcom | 13 | 0 |
V&D |
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Top DAMA Vendors |
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Rank | Vendors | DAMA | Mkt Share |
1 | Viasat | 1,000 | 70.92 |
2 | Hughes | 275 | 19.5 |
3 | Gilat | 100 | 7.09 |
4 | NSI | 20 | 1.41 |
5 | STM | 15 | 1 |
V&D |
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Top VSAT Equipment Vendors |
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Rank* | Vendors | TDMA | DAMA | Total (Rs Cr) |
1 | Gilat | 6,700 | 100 | 89 |
2 | Hughes | 2,772 | 275 | 83 |
3 | Viasat | 200 | 1,000 | 75 |
4 | ND Satcom | NA | 13 | 3 |
5 | NSI | 0 | 20 | 1.4 |
6 | STM | NA | 15 | 1 |
*Ranking based on turnover for FY 2001-02 |
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V&D |
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