Glossary of Terms
Abilene: is a project of UCAID in cooperation with several major telecommunication corporations. UCAID has organized this project, which includes participants in the Internet2 project. A primary goal of the Abilene Project is to support and foster the development of advanced applications by UCAID Members, and in particular to support Internet2. The Abilene Project will develop an advanced backbone network to connect regional network aggregation points, or GigaPops. The project is intended to complement existing research networks currently in use by UCAID member researchers and educators.
Application sharing: Application sharing is a feature that allows two people to work together when one of the individuals doesn't have the same application, or same version of the application. In application sharing, one user launches the application and it runs simultaneously. Both users can input information and otherwise control the application using the keyboard and mouse. Although it appears that the application is running on both P'Cs, it actually is running on only one, yet each user operates as though the application were running on both PC's. Files associated with the application can be easily transferred, so the results of the collaboration are available to both users immediately. The person who launched the application can lock out the other person from making changes, so the locked-out person sees the application running but cannot control it.
B
Bandwidth: A measure of the amount of data that can fit on a network. Measured in Hertz or bits per second. For example, a regular Ethernet line has a bandwidth of 10 Mbps (10 million bits per second)
Bit Rate: The speed of a communication channel, usually used when referring to modems. Most new modems follow the V.90 standard, which has a bit rate of 56kbps (56,000 bits per second)
C
CIF: A video format that supports both NTSC and PAL signals. CIF is part of the ITU H.261 videoconferencing standard. It specifies a data rate of 30 frames per second (fps), with each frame containing 288 lines and 352 pixels per line.
CODEC: Stands for Coder/Decoder (a telecommunications term) or Compressor/Decompressor (a computer term). A telecom codec is the piece of hardware that connects a data line to the customer's local network. In the computer world, a codec is a piece of software that compresses and decompresses digital audio or video.
D
Decoder: A piece of hardware or software that is used to convert video or audio (typically) from the digital form used in transmission or storage into a form that can be viewed.
E
E.164: The designation for one of the international format standards for phone numbers. An E.164 alias is simply an alias in phone number format for your video endpoint's IP address. Dialing with E.164 aliases instead of IP addresses helps maintain network security and allows endpoints to maintain dialing continuity if they do not have a static IP address or if their static IP has been changed.
F
Full Duplex: Sending data in both directions at the same time. Usually higher quality, but requires more bandwidth. In video conferencing, full duplex will be much more natural and useable. Cheap speakerphones are half duplex, whereas more expensive ones are full duplex.
Fractional T-1: FT-1 for fractional T-1 refers to any data transmission rate between 56 Kbps and 1.544 Mbps. It is typically provided by a carrier in lieu of a full T-1 connection and is a point-to point arrangement. A specialized multiplexer is used by the customer to channelize the carrier's signals.
G
G.7xx: A family of ITU standards for audio compression.
Gatekeeper: In the H.323 world, the gatekeeper provides several important functions. First, it controls access to the network, allowing or denying calls and controlling the bandwidth of a call. Second, it helps with address resolution, making possible email type names for end users, and converting those into the appropriate network addresses. They also handle all tracking and billing, call signaling, and the management of gateways.
Gateway: gateways provide a link between the H.323 world and other video conferencing system. A common example would be a gateway to a H.320 (ISDN) video conferencing system.
H
H.239: ITU standard for splitting the video bandwidth in a videoconference into two separate channels, one for media content and the other for the conference participants. It enables participants to share their computer screens or some other video source with all participants in the conference. In a multipoint conference, the content channel is viewed by all participants, and is managed by the multipoint control unit (MCU).
H.261: ITU standard for video coding for videoconferencing. H.261 is a discrete cosine transform (DCT) based algorithm for video in the 64kb's to 2mb/s range. All H.323 compliant videoconferencing systems are required to support this codec.
H.263: ITU standard for video coding within videoconferencing. H.263 offers better compression than H.261, particularly in the low bitrate range used by modem.
H.320: ITU standard for videoconferencing over ISDN and fractional T1 lines.
H.323: ITU standard for videoconferencing over networks that do not guarantee bandwidth, such as the Internet. H.323 is the standard that this cookbook is recommending that most users in the education community should be using.
H.324: ITU standard for video conferencing over standard phone lines.
Half Duplex: A telecommunications system where data can only flow in one direction at a time. Cheaper speakerphones are a good example of this, where only one person can talk at a time.
I
Internet2 (I2): A non-profit consortium that develops and deploys advanced high-performance network applications and technologies for education, research, and the next-generation public Internet. It is led by over 200 universities and partners with many affiliate members and corporate members drawn from companies in the publishing, networking and other technology industries.
IP Address: A 4-byte number uniquely defining each unit on the Internet. Forms in conjunction with the Transfer control Protocol (TCP) the TCP/IP.
Static IP: A static or dedicated IP Address is a type of account from an ISP where your computer(s) are assigned the same IP Address at all times. While this used to be a requirement for web-site serving, it is usually used today for security purposes.
IP link: The Internet Protocol. IP is the basic language of the Internet. It was developed by the government for use in internet-working multiple computer networks together.
J
Jitter: A flickering on a display screen. Besides a monitor or connector malfunction, jitter can be caused by a slow refresh rate.
K
L
Luminance: Brightness
M
MCU: In videoconferencing vernacular, a bridge connects three or more conference sites so that they can simultaneously communicate. Bridges are often called MCU's - multipoint conferencing units. In IEEE 802 parlance, a bridge is a device that interconnects LAN's or LAN segments at the data-link layer of the OSI model to extend the LAN environment physically. They work with frames (as opposed to packets) of data, forwarding them between networks. They learn station addresses and they resolve problems with loops in the topology by participating in the spanning tree algorithm. Finally, the term bridge can be used in audio conferencing to refer to a device that connects multiple (more than two) voice calls so that all participants can hear and be heard.
MPEG: MPEG (Moving Picture Experts Group) is a series of ISO Standards for digital video and audio, designed for different uses and day rates.
Multipoint: Communication: configuration in which several terminals or stations are connected. Compare to point-to point, where communication is between two stations only.
Multipoint Control Unit (MCU): A device that bridges together multiple inputs so that more than three parties can participate in a videoconference. The MCU uses fast switching techniques to patch the presenter's or speaker's input to the output ports representing the other participants.
Multipoint Conferencing Server (MCS) (also MCU): A hardware or software H.323 device that allows multiple video conferencing (or audio or data) users to connect together. Without an MCS typically only point to point conferences can take place. Commonly supports voice activated switching, where whoever is talking is broadcast to all users, but new systems support "Hollywood squares", where multiple windows show each participant. ITU-T standard H.231 describes the standard way of doing this. Many current systems only support H.320 (ISDN) but many vendors are working to upgrade their products to support H.323 (LAN, Internet) as well. In the H.320 space, this functionality is referred to as a multipoint control unit (MCU). Sometimes these terms are used interchangeably, although they refer to somewhat different implementations.
N
Network: A group of stations (computers, telephones, or other devices) connected by communications facilities for exchanging information. Connection can be permanent, via cable, or temporary, through telephone or other communications links. The transmission medium can be physical (copper, wire, fiber optic cable, etc.) or wireless, for example via satellite.
O
P
Packet: A unit of information sent across a (packet-switched) network. A packet generally contains the destination address as well as the data to be sent.
Pan: to pivot a camera in a horizontal direction,
Pixel: The smallest element of the computer or television display on the raster scale.
Q
Real-Time: The processing of information that returns a result so rapidly that the interaction appears to be instantaneous. Telephone calls and videoconferencing are examples of real-time applications. These kinds of real-time information not only need to be processed almost instantaneously, but also it needs to arrive in the exact order it's sent. A delay between parts of a word, or the transmission of video frames out of sequence, makes the communication unintelligible. The telephone network is designed for real-time communication.
S
Switched Port: This is a type of hub that forwards packets to the appropriate port based on the packet's address. Since switching hubs forward each packet only to the required port, they provide much better performance. Most switching hubs also support load balancing, so that ports are dynamically reassigned to different LAN segments based on traffic patterns.
T
T1: The transmission bit rate of 1.544 million bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 Transmission rate is 2.048 million bits per second.
T.120: This is the ITU-T standard (International Telecommunications Union) for document conferencing. Document conferencing allows two or more people to concurrently view and edit a document across a network. T>120: is the commonly used name to refer to a family of distinct standards. Many video conferencing companies were developing their own implementations of this until Microsoft released its free NetMeeting software. Now, many companies are using NetMeeting, while perhaps enhancing it in some way.
Tilt: to pivot in the vertical direction.
