Virtual Conferencing Glossary

B

B8ZS - Binary 8-zero substitution. Line-code type, used on T1 and E1 circuits, in which a special code is substituted whenever 8 consecutive zeros are sent through the link. This code is then interpreted at the remote end of the connection. This technique guarantees ones density independent of the data stream. Sometimes called bipolar 8-zero substitution. Compare with AMI. See also ones density.

B channel - The ISDN circuit-switched bearer channels, capable of transmitting 64kps of digitised information.

B-ISDN - Broadband ISDN. The ITU-T is developing the B-ISDN standard, incorporating the existing ISDN switching, signalling, multiplexing and transmission standards into a higher-speed specification that will support the need to move different types of information around the public switched network.

Bandwidth - Bandwidth primarily means a measure of data transfer speeds or as a measure of space available for data to occupy. When it comes to the Internet, bandwidth relates to the amount of information that is moved in a specific amount of time. Bandwidth is measured in thousands of bits per second (kbps) or millions of bits per second (Mbps). In videoconferencing systems a larger bandwidth is used to spread or "dither" the signal in order to prevent interference.

Bandwidth-on-demand - The ability to vary the transmission speed in support of various applications, including videoconferencing. In videoconferencing applications, an inverse multiplexor of I-Mux takes a digital signal that comes from a co-dec and divides it into multiple 56 or 64 kbps channels for transmission across a switched digital network. On the distant end, a compatible I-Mux recombines these channels for the receiving codec, and therefore en-sures that even if the data takes different transmission paths, it will be smoothly recombined at the receiving end.

Bearer mode - The type of coding or compression which the telephone network is permitted to perform on the bit stream carried on the bearer channel. In POTS, the bearer mode will always be 3.1 kHz voice. A data bearer mode implies that the data stream will not be compressed by the network (the connection is clear channel.

Binary - A method of coding in which there are only two possible values: 0 and 1 for a given digit. Each binary digit is called a "bit".

Bit - Binary Digit. The basic signalling unit in all digital transmission systems.

Bit rate - The number of bits of information transmitted over a channel in a given second. Typically expressed bps.

Bit rate allocation signal (BAS) - As specified in the ITU-T H.320 series of recommendations, bits in a frame that enable the transmission of code words to describing the capability of a terminal to structure the capacity of the channel or synchronised multiple channels in various ways and commanding a receiver to demultiplex and make use of the constitu-ent signals in such structures. The BAS signal is also used for controls and indications.

Blanking - An ordinary television signal consists of 30 separate still pictures or frames sent every second. They occur so rapidly, the human eye blurs them together to form an illusion of moving pictures. This is the basis for television and motion picture systems. The blanking interval is that portion of the television signal which oc-

Bonding - Method for making several B channels look like one high-rate line by use of an IMUX (inverse multiplexer.)

bps - bps (Bits per second). A unit of measurement of the speed of data transmission and thus of bandwidth. Actually a nested acronym, meaning binary digits per second. (lower case is significant to distinguish from Bps).

Bps - Bps (Bites per second). (8-bit) bytes per second (upper case is significant to distinguish from bps).

BRI - Basic Rate Interface. In ISDN there are two interfaces, the BRI and the PRI or Primary Rate Interface. The BRI offers two circuit-switched B (bearer) channels of 64 kps each and one packet-switched D (delta) channel that is used for exchanging signals with the network.

Bridge - In videoconferencing terminology, a bridge connects three or more conference sites so that they can simultane-ously communicate. Bridges are often called MCUs - Multiple Conferencing Units. A bridge is also considered a device that interconnects LAN's or LAN segments at the data-link layer of the OSI model to extend the LAN envi-ronment 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.

Broadband - The term applied to networks having bandwidths significantly greater than that found in telephony networks. Broadband systems are capable of carrying a large number of moving images of a vast quantity of data simultane-ously. Broadband techniques usually depends on coaxial or optical cable for transmissions. They utilise multiplex-ing to permit the simultaneous operation of multiple channels or services on a single cable. Frequently division multiplexing or cell relay techniques can both be used in broadband transmission.

Byte - A group of 8 bits.