VSAT A TUTORIAL
VSAT stands for “Very Small Aperture Terminal” and refers to receive/transmit
terminals installed at dispersed sites connecting to a central hub via satellite
using small diameter antenna dishes (0.6 to 3.8 meter).
Generally, these systems operate in the Ku-band and C-band frequencies.
Types of Operations
Bi-Directional Operation - The dish both spends (uplinks) and receives (downlinks) information.
Receive-Only Operation - The dish receives (downlinks) information only.
There are basically five types of networks employed in VSAT operations.
The Multipoint Network Structure is used in data oriented networks that require voice. The network structure provides for two-way data, voice and multi-media operations. The network configuration is a star type network that connects one or more main sites to various remote sites. It employs a central hub station and a communication satellite. Each main site uplinks and downlinks from the central hub through terrestrial (land) links. Each remote site can only uplink to the hub. If a remote site has data to send to any other location, it must first pass the information to the hub, and then it can be routed to its final destination.
This type of network is very flexible, supporting multiple interfaces available for LAN, Voice and Data connections and can support numerous transport protocols. The network employs TDMS (Time Division Multiple Access) as the means to send data to each remote site. This provides a secure means of transporting data, as each data packet contains the specific address of the station that it is addressed to and only that station can receive the data and pass it on to its network.
For Voice oriented networks a Full-Meshed Designed Network
is utilized. In a Full-Meshed there is no central hub and each site can
communicate directly with all network nodes. It employs single satellite hops
between each network nodes, which enables superior voice quality, and efficient
fast-response data connections. Since the network does not employ a central hub,
each station requires increased processing and transmission power. Each remote
must uplink and downlink with other remote sites with exactly the same size
antenna over the same radio frequency.
Hybrid Voice and Data Network
This type of network is a hybrid between the Multipoint
and Full-Meshed network. Like the Full-Meshed Network it does not contain a
central hub, though it provides all remote sites with the capability to
communicate direct with all other sites . It provides the ability to offer
voice, fax, and videoconferencing opportunities between the sites. Data and
video can be broadcast is bi-directional between the central hub and the remote
site. This system takes separate voice and data interfaces at the remote site
and then processes this and combines them onto a single cable connecting to the
antenna. The remote HES VSAT acts as a switch routing all connections to their
appropriate destination. The system is capable of a wide-range of advance
telephony and PBX voice services and provides an efficient LAN/WAN network
Single Channel Per Carrier (SCPC) - Point-to-Point
SCPC circuits are point-to-point circuits that provide two-way communication between VSAT terminals located at two sites. It is a very flexible system and has the capability to handle multiple data types over multiple protocols. The system can handle voice, fax, and video application. the data rates range from 9.6 kbps up to 8.4 Mbs. It is ideally suited for bringing Internet to remote ISP sites. Internet access is provided through one satellite dish connected to the Internet through a point-to-point line and transmission is accomplished between it and another terminal at the remote ISP through the use of a satellite. This system is capable of both asymmetric and well as symmetric connections.
Broadcast Networks provide for the transmission of data, video and audio files to any number of users. The system "broadcasts" from the central site to the end user remote sites. This one-way system provides an uplink from the central site and each remote site downlinks (receives) only. It provides high speed channel that is capable of up to 24Mbs up linked, providing this information to numerous units.
ODU (Outdoor Unit): consists of the dish/reflector antenna and Feed horn which contains either an LNB for receive only systems or a LNA for bi-directional systems, which amplify the signal received by the unit. Other electronic components consists of a Transmit Reject Filter, Up/Down Converter (Transceiver), High Frequency Power Amplifier, and Transmit Type N Transition. These components are either packaged separately or packaged together in a single unit, depending on the manufacturer.
IDU (Indoor Unit): consists of the electronic
interface that allows connection to the network. It provides the interface.
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