anies, in the US, a transmission.) who provide operator services in competition with African, Caribbean, Pacific. (Group of Third World existing suppliers such as AT&T and the RBOCs.) countries who have special arrangements with the Australian and Overseas Telecommunications Cor- European Community.) poration. (Australian PTT.) Accredited Standards Committee. (ANSI) Asian-Oceania OSI Workshop on Standards. Association Control Service Element. (OSI applica- (Asian/Pacific area functional standards making tion.) group.) Approvals Committee for Terminal Equipment. APNSS Analogue Private Network Signalling System. (Part of European Community.) Application Processes. (Processes within computer Australian CCITT Committee. based systems which perform specified tasks.) Automatic Call Distribution. (Facility for allowing Aeronautical Public Correspondence. (CCIR term incoming calls to be queued and distributed to wait- for airborne communication systems.) ing service operators.) Adaptive Predictive Coding. Analogue to Digital Conversion. Avalanche Photodiode. (A semiconductor device Automatic Digital Distribution Frame. (System used used for fibre optic communications.) to replace manual distribution frames in plesio- Application Programming Interface. chronous transmission networks.) Amplitude Phase Keying. (A digital modulation Adaptive Delta Modulation. (Digital signal modula- technique in which the amplitude and phase of the tion technique.) carrier are varied.) Add-Drop multiplexer. (Term sometimes used to Asia Pacific Telecommunity. describe a drop and insert multiplexer.) Advanced Research Project Agency. (Agency oper- Automatic Data Processing. ating within the US Department of Defence.) ADPCM Addaptive Differential Pulse Code Modulation. Automatic Request for repetition. (A feature in (CCITT standard for the conversion and trans- transmission systems in which the receiver automat- mission of analogue signals at 32kbit/s.) ically asks the sender to retransmit a block of infor- Anomaly Events. (E.g. frame errors, p