VSAT Technology

Useful technology terms:

AD HOC: Industry term for on-demand verses full-time services.

AMPLIFIER: A device used to increase the strength of electrical signals.

ANALOG: A form of transmitting information characterized by continuous and variable signal levels. Off-air broadcast TV is an example of analog signals.

ANTENNA: The device that sends and/or receives signals from the satellite. Also referred to as a satellite dish.

ASYMMETRIC CIRCUIT: A two-way satellite link with inbound and outbound paths set at different rates.

AZIMUTH: The horizontal angle between true north and an antenna pointing, with true north set to 0.0 degrees, and due south set to 180 degrees.

BANDWIDTH: The amount of spectrum a communication channel (analog or digital) uses, measured in hertz (Hz).

BEAMWIDTH: A measure for the pointing accuracy of a satellite antenna, in degrees. Large antennas have smaller beamwidths, while smaller antennas have larger beamwidths.

BIRD: A nickname for a satellite.

BIT: A single unit of information in the binary system which takes on the value of 1 or 0.

BROADBAND: A term used to refer to high-speed communication networks that are designed to handle bandwidth-intensive applications.

BROADCASTING: To transmit a signal to multiple locations simultaneously over satellite, radio/TV station, data communications network or e-mail system.

CARRIER: 1) A telephone long distance company that operates fiber/satellite/microwave networks to carry voice and data traffic. A local exchange carrier (LEC) is a local phone company and an inter-exchange carrier (IEC or IXC) carries long-distance calls. 2) A continuous radio frequency (RF) signal used to carry another information signal.

CACHE: A place to store something temporarily. Web pages you request are stored in your browser’s cache directory on your hard disk. When you return to a page you’ve recently viewed, the browser gets it from the cache rather than the original server, saving you time and the network additional traffic. You can usually vary the size of your cache, depending on your particular browser.

CACHE SERVER: A server relatively close to Internet users and typically within a business enterprise that saves (caches) Web pages and possibly FTP and other files that all users have requested. Successive requests for these pages or files can be satisfied by the cache server rather than the Internet. A cache server not only gets information more quickly but also reduces Internet traffic.

C-BAND: Refers to the frequency in the 3.4 GHz to 7 GHz range. Portions of this band are dedicated to satellite communications. Satellite downlinks are 3.7 to 4.2 GHz.

CHANNEL: Path for electrical communication between two facilities. Also called a circuit, link or path.

CIRCUIT: A satellite link.

CIRCULAR POLARIZATION: A mode of transmission in which signals are downlinked in a rotating corkscrew pattern.

CO-LOCATION: Placement of more than one satellite at the same orbital location. From the ground, they appear as one satellite that can receive with a single antenna, provided they use the same frequency band.

COMPRESSION: Reducing the amount of bandwidth needed to transmit video or audio by digitizing an analog signal, thus increasing the ability to load multiple services on a satellite transponder.

DAMA: Demand Assigned Multiple Access. A bandwidth-sharing scheme allowing multiple users to share a pool of frequencies or channels on demand. A central hub manages the usage of the bandwidth. This technology is mainly used for rural telephony.

DECODER: A device used to unscramble encrypted or “scrambled” television signals.

DELAY: The time it takes for a signal to travel from a transmitting earth station, through space, to a satellite and back. This time calculates to be about � of a second.

DIGITAL: A quantification scheme that allows the conversion of analog information into bits of data. Digitization allows for signal compression and for maintaining signal integrity.

DISH: See antenna or earth station

DOWNLINK: The transmission of radio frequency signals from a satellite to an earth station.

DSL: Digital Subscriber Line. A technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines. A home or small business close enough to a telephone company central office that offers DSL may be able to receive data at rates up to 6.1 megabits (millions of bits) per second. This enables continuous transmission of motion video, audio, and even 3-D effects. More typically, individual connections will provide from 512 kbps to 1.544 Mbps downstream and about 128 kbps upstream. A DSL line can carry both data and voice signals, and the data part of the line is continuously connected.

DUPLEX: Method in which transmission is possible in both directions of a telecommunications channel. Simultaneous two-way operation is known as “full duplex”. Operating in only one direction at a time is known as “half duplex” or “simplex.”

EARTH STATION: A ground-based antenna and associated equipment used to receive and/or transmit telecommunications signals via satellite.

EIRP: Effective Isotropic Radiated Power. Refers to the measure of the satellite signal strength on the ground in reference to an isotropic source.

ELEVATION: The angle between an antenna beam and the horizontal plane.

ENCRYPTION: Process of electronically ciphering a signal so it cannot be received without a decoder.

FIBER: Fiber optic (or “optical fiber”) refers to the medium and the technology associated with the transmission of information as light impulses travel along a glass or plastic wire or fiber. Fiber optic wire carries more information than conventional copper wire and is less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic.

FOOTPRINT: The coverage area of the earth’s surface within which the signals of a specific satellite can be received.

FREQUENCY: The rate at which a signal (e.g. electrical current) alternates. The standard unit of frequency is the hertz, abbreviated Hz. If a signal completes one cycle per second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz.

  • Hz: Hertz. The name of the basic measure of frequency at which an electromagnetic wave completes a full cycle from its positive to its negative pole and back again. Each unit is equal to one cycle per second.
  • KHz: Kilohertz. Refers to a unit of frequency equal to 1,000 Hertz.
  • MHz: Megahertz. Refers to a frequency equal to one million Hertz.
  • GHz: Gigahertz. Refers to a frequency equal to one billion Hertz.

FDMA: Frequency division multiple access. Refers to the use of multiple carriers within the same transponder where each uplink has an assigned frequency slot and bandwidth.

GEOSTATIONARY SATELLITE: A satellite orbiting 36,000 kilometers (22,300 miles) directly over the earth’s equator. From earth, a geostationary satellite always appears to be in the same location because it finishes one rotation around the earth in 24 hours. Fuel on board the satellite is used to perform the “station-keeping” function, which maintains the satellite within a prescribed location, or box.

GMT: Greenwich Mean Time. The time zone that includes Greenwich, England is bisected by zero degrees longitude. This is the time notation that is used for booking international satellite time.

GPS: Global Positioning System. A satellite system that provides precise reference to the location of a point on earth. GPS satellite systems employ lower orbiting satellites than geostationary satellite networks.

HEADEND: Location where cable television systems collect and distribute satellite programming. HOPS: The number of routers or gateways on any given path.

HUB: The point on a network where circuits are connected or a network operations center for very small aperture terminal (VSAT) operations.

HYBRID SATELLITE: A satellite that carries two or more different communications payloads (i.e. C-band and Ku-band).

INTERNET BACKBONE: The network spanning the world that is provided by a handful of national Internet Service Providers (ISPs). They use connections running at approximately 45 megabytes per second linked up at specified interconnection points called national access points. Local ISPs connect to this backbone through routers, so data can be carried through the backbone to its final destination.

INTERNET GATEWAYS: A network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company’s network or at your local ISP are gateway nodes.

IP: Internet protocol (IP) is the method by which data is sent from one computer to another on the Internet. Each computer on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. When you send or receive data (for example, an e-mail note or a Web page), the message gets divided into little chunks called packets. Each of these packets contains both the sender’s Internet address and the receiver’s address.

ISDN: Integrated services digital network. A standard for the integrated transmission of voice, video, and data developed by the Consultative Committee on International Telephony and Telegraphy (CCITT).

ISP: Internet Service Provider. A vendor who provides access for customers (companies and private individuals) to the Internet and the World Wide Web. Users typically reach their ISP by modem and phone line.

IT: Information technology. All equipment, processes, procedures and systems within an organization and those reaching out to customers and suppliers. JAMMING: Deliberate interference with a signal caused by another signal transmitted in the same frequency.

JPEG: Joint pictures expert group. A subgroup of ISO, which has established international standards for the digital compression of still pictures.

Ka-BAND: Primarily used in satellites operating at 30GHz uplink and 20 GHz downlink and is intended in support of future applications such as mobile voice. A portion of the RF spectrum located between 18 GHz and 31 GHz.

Ku-BAND: Refers to the frequency in the 12 GHz to 14 GHz range used in support of such applications as broadcast TV, DBS, and direct-to-home television.

LAN: Local Area Network. A local area network (LAN) is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network).

L-BAND: A portion of the RF spectrum located between 500MHz and 1500MHz.

LEASED LINE: A dedicated circuit typically supplied by the telephone company.

LEO: Low earth orbit. An orbit 150 km to 300 km from the earth’s surface.

LNB: Low noise blockdownconverter. An electronic part of a satellite earth station that is used to amplify the signal collected by the reflector and the feedhorn.

MCPC: Multi-channel per carrier. A signal comprised of multiple digital streams that are multiplexed into a single stream, which is then transmitted on a single carrier. This is typically used to combine multiple CDV signals into one.

MPEG: MPEG, the Moving Picture Experts Group, develops standards for digital video and digital audio compression. It operates under the auspices of the International Organization for Standardization. The MPEG standards are evolving, each designed for a different purpose.

MULTI-CAST: The broadcast of messages to a selected group of workstations on a LAN, WAN or the Internet. Multicast is communication between a single device and multiple members of a device group.

MULTIPLEXING: A technique that combines multiple signals into one signal.

NASA: National Aeronautics and Space Administration.

NOISE: Energy always present on any signal.

ORBITAL SLOT: Specific location of a satellite in the geostationary arc, specified in degrees, east or west.

PAYLOAD: Supports the primary mission of the satellite, the receipt and transmission of signals, and comprises systems that include receivers, multiplexers, high-powered amplifiers and signal processing.

PLATFORM: A structure in space containing multiple missions. A software operating system and/or open hardware, which an outsider could write software for.

POLARIZATION: The orientation of a transmitted/received signal. Signals can have circular or linear polarization.

ROUTER: An intelligent device that supports connectivity by “routing” packets of information to their destination. Routers ensure that packets always arrive at their proper destination.

SCPC: Single Channel Per Carrier. A scheme in which only one signal is loaded on a carrier.

SHARED HUB: A satellite communications operations center that is shared among a number of separate network users, often used for VSAT operations.

SOLAR PANEL: A device on satellites that converts solar energy into electrical energy using solar cells.

SPACE SEGMENT: A term that describes the portion of the total communications satellite system that is physically located in orbit around the earth.

SPECTRUM: The range of electromagnetic radio frequencies used in transmission of voice, data and television.

SPOT BEAM: A satellite antenna designed to direct all of the satellite’s power to a relatively compact area on earth.

SPOTbytes Internet connections: A bundled package, offering backbone network operators, international ISPs and corporate customers a one-stop shopping resource for satellite space segment, gateway transmission services and a dedicated Internet backbone connection.

STATIONKEEPING: The process of making in-orbit adjustments with small rocket thrusters attached to the satellite, keeping the satellite in its correct geosynchronous position.

STREAMING: Streaming video is a sequence of “moving images” that are sent in compressed form over the Internet and displayed by the viewer as they arrive. Streaming media is streaming video with sound. With streaming video or streaming media, a Web user does not have to wait to download a large file before seeing the video or hearing the sound. Instead, the media is sent in a continuous stream and is played as it arrives. The user needs a player, a special program that uncompresses and sends video data to the display and audio data to speakers. A player can be either an integral part of a browser or downloaded from the software maker’s Web site.

SUN OUTAGE: When the sun passes behind a satellite in relation to the earth, and the sun’s energy momentarily interferes with the satellite signals. Occurs two times each year during the spring and fall equinox.

SYMMETRIC CIRCUIT: A two-way satellite link with inbound and outbound paths set at the same rates.

TCP: Transmission Control Protocol. TCP (Transmission Control Protocol) is a method used along with the Internet protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet.

T-1: Refers to bit rate of 1.544 million b/s for the United States. The European E-1 transmission bit rate is 2.048 Mb/s.

TDMA: Time Division Multiple Access. A form of multiple access where a single carrier is time-shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.

TELEPHONY: The transmission of speech to distant places.

TELEPORT: Technical ground facility used for satellite communications.

TRACKING: An earth station feature that allows for tracking inclined satellites.

TRANSPONDER: A radio frequency path through a satellite with a specific bandwidth, uplink/downlink frequency and beam. Transponders can be sold in whole or can be segmented into smaller pieces of bandwidth.

TURNKEY: Refers to a system that is supplied, installed and sometimes managed by one vendor or manufacturer.

UHF: Ultra high frequency. The band in the 500 to 900 MHz range, including television channels 14 through 83.

UPLINK: The transmission of radio frequency signals to a satellite from an earth station VHF: Very high frequency. The band in the 30 to 300 MHz range, including television channels 2 through 13.

VPN: A virtual private network is a private data network that makes use of the public telecommunication infrastructure, maintaining privacy by encrypting data before sending it through the public network and decrypting it at the receiving end. A virtual private network can be contrasted with a system of owned or leased lines that can only be used by one company. The idea of the VPN is to give the company the same capabilities at much lower cost by using the shared public infrastructure rather than a private one.

VSAT: Very small aperture terminal. Refers to small earth stations, usually 3 feet to 6 feet (0.9 meter to 1.8 meter) in diameter. A VSAT system is a satellite communications system that is typically used for corporations or rural telephony. A VSAT system consists of an antenna and the associated electronics. VSAT networks are widely used by department stores, gas stations and drug stores for verifying credit cards. VSAT systems can be used for voice, data and video.

X-BAND: A portion of the RF spectrum located between 7 GHz and 8 GHz, which is dedicated to the U.S. military for satellite communications.

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