element within the OSI seven layer Duplex. System which is able to carry traffic in both directions reference model which uses the services of the next lower layer simultaneously. to communicate with another peer entity. Duty class. Usually used with reference to network management Epitaxial layer. A relatively thin layer of semiconductor with a systems, which defines the scope of management facilities closely defined chemical structure, which is formed on the available to a user within different duty classes. surface of a semiconductor substrate. Dynamic range. The range available to a signal before it will result Equalisation. Process for compensating for transmission distor- in overload. It is measured as the difference between the mini- tion using fixed or adaptive circuitry. mum acceptable signal level and the value at which overload Equity capital. US term for money raised by a company by selling occurs. its stock. See also debt capital. Equivalent circuit. An electrical circuit which is used to simulate the behaviour of an electronic component. Erlang. Unit of measure used to define telecommunications traffic density. It is a measure of the average call traffic on a line for a E1. Digital trunk used in Europe carrying 32 channels at 64kbit/s period of time. One Erlang is equivalent to one circuit being each. occupied for one hour. E&M signalling. A basic analogue signalling method using two Error burst. A sequence of errors occurring within a transmitted wires designated E and M. (E&M stands for Ear and Mouth.) signal. Often taken to represent a single error in error measure- Earth station. Refers to the site containing radio equipment, which ment systems. is used for sending and receiving information from a satellite in Ethernet. A popular local area access system, standardised by the orbit. IEEE as 802.3. 62/24 Glossary Event. Usually refers to any occurrence which is reported by a Foreign potential. Undesirable voltage which is introduced into managed element to its manager within a network management t