Glossary   Asymmetric interactivity - Interactivity is asymmetric when the communication paths are dissimilar as, for instance, when voice and video are outbound from the instructional site and the students return voice only. For both pedagogical and economic reasons, the flow of content is usually much heavier from instructor to the students. BTV - Business television. TV programs, often developed internally within and about a particular company, delivered over a private network. The typical case for establishing a BTV network involves motivation, information, or training opportunities which reducing cycle time and travel costs. Asynchronous - Literally, "not at the same time." Distance learning can be delivered three ways -- live, asynchronously, or a combination of the two. Likewise, interactivity may be provided in the same three ways. Asynchronous interactivity may present special challenges on both the technical and the teaching sides. E-mail or fax is a relatively low tech form of asynchronous interactivity. In more developed systems, asynchronous interactivity may be assimilated with "live" responses in a database. The ability to deliver instruction and interactivity asynchronously is an important element of customer convenience and, hence, economy of scale for the entire network. Beam - The directed radio waves emanating from a transponder. Typically refers to aggregates of these rays, such as a "Latin American" coverage beam. Bird - Alternative or informal name for a satellite. Datacasting - The transmission of digital data. Generally datacasting refers to often large computer files. Streaming technology is such, though, that increasingly datacasting includes encoding audio and video as digital data files. Datacasting is distinct from TVRO. Distance learning - A broad term describing an instructional situation where teachers and students are physically separated. Historically this encompassed correspondence courses and other paper-based approaches. Implicit today is electronic transmission--perhaps by satellite, cable, terrestrial Internet, etc. Downlink - Equipment used to receive transmitted satellite signals from space back down to earth. Essential to a downlink is an antenna ("dish"), a Low-Noise Block (LNB) downconverter, and integrated Receiver/Decoder (IRD). Footprint - The area of the earth within which a satellite's signal can be easily received. This area is determined both by geography (there must be "line of sight" to the satellite) and shape of the transponder beam. Interactivity - Interactivity involves two-way communications. Traditionally that two-way communication is live between instructor and student, but it may also be peer-to-peer communication in a collaborative learning environment. The communication may take the form of voice, data, video, or audio. See also, asymmetric and asynchronous. Internet - This electronic network connects servers so that you may go from one Web page to another efficiently. The electronic connection began as a government experiment called ARPANET in 1969 with four computers hooked together over phone lines. By 1972, universities also had access to what was then called the Internet. In the mid-1990's, with the advent of Web browser technology, the Internet became an important global commercial and educational force. See also the section Internet Technology. IRD - Integrated Receiver Decoder. A combined radio frequency receiver and (usually) MPEG decoder that is used to adapt a digital satellite transmission for use on a TV-set or other device. Life of bird - The expected end of a satellite's in-orbit operational life. Usually determined by the anticipated period during which the satellite's on-board fuel permits proper station-keeping maneuvers for the satellite. Life of bird has steadily increased from 3-4 years to, presently, about 12 years. Link budget - An engineering task wherein all of the technical factors associated with the uplink, transponder, and downlink are analyzed to insure the network will meet expectations and operate optimally. LNB - Low Noise Block downconverter. Amplifies signals and converts them to microwaves which are then sent down a cable to the receiver. Sometimes also called a feedhorn, though technically the feedhorn is just outside the LNB. Satellite - A geostationary satellite is an electronic relay station orbiting 22,237 miles above the equator, moving in a fixed orbit at the same speed and direction of the earth, about 7,000 miles per hour east to west. Transponder - The part of a communications satellite that receives signals from the earth, alters their frequency, amplifies the signal, and sends them back to earth. The word originates from transmitter and responder. TVRO - Television Receive-Only. An earth station designed to receive only television transmissions. VSAT - Very Small Aperture Terminal. A small earth station, usually from 1.2 to 2.4 meters, used for satellite data communications. One form of datacasting. In common practice, the VSAT label does not so much establish the size of the dish as it indicates two-way data communication. Retail credit card authorizations are a widespread application of VSAT technology.
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