OPENSKY™ Glossary

Here you can find all technical terms we could use talking about our services.



Representation of a value or quantity as a continuous variable. In contrast, digital representations consist of values measure at discrete intervals. E.g., analogue computers measure, analyse and compute using actual measurements and numbers (see Digital). Analogue electrical signals (such as the radio frequencies used to transmit telecommunications information) are directly generated in the form of sound or light waves.

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A measurement in bits per second (digital transmission) or in Hertz of the amount of data that can be sent over a cable, interface or network.
Any form of transmission in which everyone connected to a particular service simultaneously receives the same signal. In the broadcasting-satellite service, signals are transmitted or retransmitted by space stations for direct reception by the general public (direct reception includes both individual reception and community reception).

Any form of transmission in which everyone connected to a particular service simultaneously receives the same signal. In the broadcasting-satellite service, signals are transmitted or retransmitted by space stations for direct reception by the general public (direct reception includes both individual reception and community reception).

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Describes any system based on discontinuous data transmitted as a sequence of discrete signals from a finite set. At their most basic level, computers can distinguish between just two values, 0 and 1, or off and on. There is no simple way to represent all the values in between. All data processed by a computer has to be encoded digitally as a series of 0's and 1's.

Describes physical location in relation to another entity or device. For example, a small ISP that connects to the Internet through a larger ISP that has its own connection to the backbone is downstream from the larger ISP, and the larger ISP is upstream from the smaller ISP.

A telecommunications term that describes communications between terminals capable of transmission in both directions. A half-duplex communication channel can, at any given time, carry data in either one direction or the other, but not both. A full-duplex channel can carry data in both directions at once. In full duplex mode, the remote computer is set up to return the characters that are sent to it so that they can be displayed on your screen. In half-duplex mode, the remote computer does not return the characters.

DVB (Digital Video Broadcasting)
Common international standards for the move from analogue to digital, established by a consortium of around 300 companies in the fields of broadcasting, manufacturing, network operation and regulatory matters. This joint market-led initiative has resulted in DVB becoming a prominent and leading international standard and the sole choice for technologies that enable an efficient, cost-effective, easy/rapid transition, higher quality and interoperable digital broadcasting.

DVB adapter
An adapter capable of receiving data broadcast over a satellite network (e.g. via the Internet). The adapter should have these features: fully compliant with MPEG-2 based DVB transmission standards, fully-universal compatible tuner 900-2150 MHz, QPSK demodulator, extended symbol-rate (2-45 MS/s), MCPC/SCPC capable, support for DiSEqC* 1.0 LNB control, fully-compliant with DVB data-broadcasting specification (ETSI EN 301 192), support of IP unicasting and multicasting. It can be an internal device such as a PCI adapter or an external device such as a USB box.

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A device that converts for instance an analogue signal to a digital signal representing equivalent information. Synonym: analogue-to-digital.

Refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. Extranets are external extensions of a company's intranet that allow certain people to interact from the Internet.

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File Transfer Protocol. A higher level protocol, used in conjunction with TCP/IP (see later).

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A combination of hardware and software that links two different types of networks.

Internet Backbone
Term used to describe the main network connections that allow Internet traffic to be carried around the world. The Internet Backbone often has to operate at a higher speed than the rest of the network as it connects all the other segments.

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A corporate network based on TCP/IP Protocols and accessible only by the company's employees or others with authorization. An intranet's web site looks and acts just like any other web sites, but the firewall surrounding an intranet fends off unauthorized access. Intranets are used to share information within the company. Think of it as a mini, private Internet.

IP Address
The specific network address of a computer on a network using TCP/IP as its network protocol.

ISP (Internet Service Provider)
An ISP provides Internet access for individuals or companies. ISPs charge users a monthly fee and generally operate via modem and dial-up connection requiring a username and password. Smaller ISPs buy bandwidth from larger ISPs.

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Modem (MOdulator, DEModulator)
A device that you connect to your computer and to a telephone line, allowing the computer to talk to other computers. Basically, modems do for computers what a telephone does for humans.

MPEG is short for Moving Picture Experts Group. The term refers to the family of digital video compression standards and file formats developed by the group, used in conjunction with desktop computers for video presentations. MPEG-4 (the latest version) has a higher compression rate than MPEG-2.

Multicast data, once requested by one person, can be received by any number of people. Multicasting is therefore a very efficient way of sending data from a single server to millions of simultaneous users. Once the data stream is being broadcast, any other user can choose to select the same stream after receiving the necessary parameters from the originating server. This gives service providers the choice of providing the content free-of-charge, on a subscription basis or via pay-per-view. Content providers can therefore “push” their content over satellite for reception. This solution is ideal for web broadcasting of, for example, weather, news, financial information and sports, as well as for audio/video streaming and customized services. No return link is required.

The use of computers to present text, graphics, video and sound in an integrated way. In simpler terms, this refers to the basic functions of sound cards and video cards. The term also covers TV reception via computer.

Multiplexer (Mux)
A communications device that multiplexes several signals for transmission over a single medium. In the world of networks, it is used to describe devices that send several signals over a single line at the same time. A demultiplexer completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexer and demultiplexer are combined into a single device capable of processing both outgoing and incoming signals.

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A relatively small unit of data transmitted over a network as part of a message. Packets travel independently of one another and maybe by different routes. They are reassembled as a coherent message at the point of reception.

Proxy server
A server that sits between a client application such as a Web browser and a real server. It intercepts all requests to the real server to see if it can fulfil the requests itself. If not, it forwards the request to the real server. Proxy servers can dramatically improve performance for groups of users because they store the results of all requests received for a certain amount of time. The server on the Internet has no indication that the request is being submitted other than by the proxy. Some proxies also have caching and site-filtering built in.

Pull technology is where a user sends a request for data to a program or computer. The opposite of pull is push, where data is sent without a request being made. The terms push and pull are used frequently to describe data sent over the Internet. The World Wide Web is based on pull technologies, where a page is not delivered until a browser requests it. Increasingly, however, information services and electronic marketing are harnessing the Internet to broadcast information using push technologies.

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A device that bridges an internal network to another network. For example, it is used to bridge a computer to a long distance digital communications network, such as ISDN.

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A technique for transferring data (usually over the Internet) in a continuous flow to allow large multimedia files to be viewed before the entire file has been downloaded.

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TCP/IP (Transmission Control Protocol/Internet Protocol)
This is the suite of protocols that defines the Internet. Originally designed for the UNIX operating system, TCP/IP software is now available for every major kind of computer operating system.

A combined transmitter and receiver on a communication satellite. A frequency converter is also included in the transmit/receive package to convert the uplinked signal frequency to a different downlink frequency.

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VSAT (Very Small Aperture Terminal)
Earth station satellite antenna with a diameter usually from 1.2 to 2.4 metres.