VSATs: As You Like It

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.

VOICE&DATA Corporate Expectation Survey 2003

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
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
V&D Estimates

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.

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
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 Estimates

Top DAMA Vendors
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 Estimates

Top VSAT Equipment Vendors
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
V&D Estimates

CONSULTING BOARD Amit Tripathi, V-P (DIrecway Global Education), Hughes Escorts Communications Limited Feroze Khan, country manager (India and Southeast Asia), Viasat Satellite Networks Sanjeev Nikore, COO (Asean), HCL Comnet