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		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