Distance education glossary

• Asynchronous: Communication in which events between parties are not synchronized, or coordinated, in real time.

• Asynchronous Transfer Mode (ATM): A connection-oriented switching technology in which data transfer occurs over a specific virtual circuit.

• CIF: Short for Common Interchange Format (or Common Intermediate Format), a video format used in videoconferencing systems that specifies a data rate of 30 frames per second (fps), with each frame containing 288 lines and 352 pixels per line. CIF specifies the minimum number of lines that are actually required in order for the human eye to perceive video that is at least broadcast quality. Video that does not meet the CIF standard will appear blurred, with jerky, unnatural motion and audio that does not match the video being viewed.

• Codec: Hardware or software that converts analog sound, speech, or video into digital code, and vice versa. The term “codec” is a double acronym: COmpressor/DECompressor and COder/DECoder, as it fulfills both roles in usage.

• Desktop videoconferencing: Videoconferencing using a personal computer. Users may employ the H.323 standard (over the internet or another TCP/IP network) or the H.320 standard (over dedicated or dial-up digital circuits). A few systems can use either standard.

• Distance education: The process of providing instruction to students and teachers separated by physical distance. Technology is used to bridge the gap between learners and instructors.

• Distance learning: Frequently used in place of the term “distance education,” this term actually refers to the desired outcome of distance education.

• DS3 (or T3): A classification of digital circuits. Used synonymously, “DS” refers to the rate and format of the signal and “T” refers to the equipment providing the signals. One DS3 equals twenty-eight T1 lines and is normally used as a backbone to the internet by internet service providers and large bandwidth users.

• H.261: An ITU standard for compressing an H.320 videoconferencing transmission.

• H.263: An ITU standard for compressing an H.323 videoconferencing transmission.

• H.320: A standardized compression method and real-time protocol for the transmission of audio, video, and data over digital lines. Using the H.261 compression method, H.320-compliant videoconferencing room and desktop systems communicate with each other over ISDN, switched digital, and leased lines.

• H.323: A standardized compression method and real-time protocol for the transmission of audio, video, and data between videoconferencing codecs over the internet or other TCP/IP based network. H.323 sets standards for multimedia communications over local area networks (LANs) that do not provide a guaranteed quality of service (QoS).

• ITU (International Telecommunication Union): The ITU, headquartered in Geneva, Switzerland, is an international organization within which governments

and the private sector coordinate global telecom networks and services. It is responsible for establishing interoperability standards for communications equipment.

• Latency rate: The delay between when the signal is sent and the image is received. True real-time latency (low enough as not to be perceptible to the human eyes and ears) is about 150-200 milliseconds (mS); practical systems can have a 400 mS latency and still provide good conference interaction.

• MPEG (Moving Pictures Experts Group): An ISO/ITU standard for compressing video. MPEG-1, which is used in CD-ROMs and video CDs, provides a resolution of 352 pixels by 288 lines (352 x 288) at 30 frames per second (fps) with 24-bit color and CD-quality sound. MPEG-2 supports a wide variety of audio/video formats, including legacy TV and high-definition television (HDTV), and is used in DVD movies. MPEG-2 requires from 4 to 15 megabits per second (Mbps) of bandwidth. There is no MPEG-3. MPEG-4 is the next generation MPEG and it will permit a wide range of audio and video modes and transmission speeds.

• Multipoint control unit (MCU): A “video bridge” that connects multiple sites and stations for videoconferencing. This bridge device joins the lines and switches the video either automatically, depending on who is speaking, or manually, under the direction of a moderator.

• Origination site: The location from which a teleconference originates.

•Point-to-point: A conference or transmission between two sites, often one-way with an origination and receiving site.

• Point-to-multipoint: A communications network that provides a path from one location to multiple locations. Depending on the type of point-to-multipoint teleconferencing system, the receiving sites may have the ability to transmit back to the other receiving sites as well as the originator. Regular broadcast television is an example of point-to-multipoint transmission.

• Synchronous: Communication in which events are synchronized, or coordinated, in real time.

• T.120: An ITU standard for real-time data conferencing among multiple users. It is an umbrella term for a series of specifications that define all aspects of data conferencing, including interfaces for whiteboards, application viewing, and

application sharing.

• Teleconferencing: To hold an interactive communications session in real-time via a telephone or network connection between users that are geographically separated. Examples include videoconferencing, audioconferencing, audiographic conferencing, and computer conferencing.

Want to share a great resource? Let us know at submissions@eschoolmedia.com.