transmitting and receiving stations are sychronised equipment, such as a switch, than exist on external links. and no stop or start information is used. Timing diagram. A diagram which shows the change of state of Syntax. Usually refers to the sturcture used within a communica- signals over a period of time. tion message, such as the data format, signal levels, coding, etc. Token passing. Access method used in LANs, where a device has the right to transmit data only when it is holding a 'token'. The token is passed sequentially to all elements on the LAN. The network may be arranged as a bus (known as token bus) or ring (called token ring). T1. Digital trunk, used in North America, carrying 24 channels at Toll centre. Term used in the US for a Class 4 telephone central 64kbit/s each (1.544 Mbit/s). office. T2. Digital trunk, used in North America, and operating at Traffic density. A measure of the number of calls which are being 6.312Mbit/s. made at any instance in time. Talker echo. Echo in voice systems which is perceived by the Traffic intensity. Usually expressed as the product of the calling talker or sender. It occurs when the talker's speech is returned rate and the average holding time. It is expressed in Erlangs. with significant delay. Trailing edge. The side of a signal which occurs after the leading Talking battery. A battery which is isolated from other battery use edge. The falling amplitude part of a signal pulse. See also so that it is electrically quiet and allows good quality voice leading edge. communication. Transceiver. Device which can transmit and receive information. 62/32 Glossary Transhybrid loss. A measure of the isolation, in decibels, between Uptime. The time for which a resource is working and available the go and return paths on the four wire side of a two wire to to users. four wire hybrid. Transient. Usually refers to an intermittent, unwanted signal, which lasts for a short duration and often causes interference Vestigial sideband transmission. A single sideband transmission with