ute with a remote device. Bipolar. Within telecommunications it refers to a signalling Autodial. The ability of a terminal, such as a modem, to autono- method for digital transmission where the signal carrying the mously place a call over the switched telephone network. data alternates between a positive and a negative polarity. Automatic call distribution. System used to switch incoming calls Bipolar. A type of semiconductor technology which uses both the evenly and automatically to a number of stations on a first come positive and negative charged currents. See also unipolar. first served basis, so minimising the waiting queue. Bistable. A component or system which is stable in either one of Automatic route selection. Capability of a device to automat- two modes. See also monostable. ically select the most optimum route to send information. Bit. Smallest form of binary data. 62/20 Glossary Bit duration. A measure of the time taken by an encoded bit to Bus. A transmission path, channel or media to which several pass a point in a transmission medium. It is often used as a devices may be connected to receive simultaneous trans- means for comparing delay times within various transmission mission. Example is a local area network bus. media or elements. Busy hour. Period when the maximum number of calls are ex- Bit error. The instance when the value of an encoded bit is pected through a telephone system. It is the uninterrupted changed during transmission and therefore incorrectly inter- period of sixty minutes during which the traffic is at the maxi- preted by the receiver. Bit error rate. A measure of the proportion of transmission bits Bypass carrier. USA based local carrier who provides an alterla- which have an error. Usually expressed as a number to the tive to the LEC, connecting large businesses to one or more power of 10, e.g. 1 in 10 bits. IXCs, usually using fibre optic and metropolitan area networks. Bit oriented. A transmission protocol in which the control infor- Byte. This consists of eight bits. It is