61/11 57/13 Centrex, 35/3 TDM, 21/8, 21/11, 40/6 D3 digital composite digital tape format, voice processing with, 37/6 CRC-4 cyclic redundancy check, TDM, 57/12 DDS (Dataphone Digital Service), Bell's, 21/10 D layer/region, 9/3-5, 9/6, 27/6, 27/8 21/14-15, 56/5 Critical frequency, ionosphere, 6/21 see also lonosphere Debugging software, 25/16 Cross modulation, ionosphere, 6/21 D screen cable, 15/5 Decca navigation system, 9/6 Cross polarisation discrimination (XPD), D-MAC television audio, 57/8-10 Decentralised adaptive routing 6/19-20 D/A converter see DAC strategy, 5/10 Crossbar exchanges, 31/11-12, 32/3-7 DAC (Digital to Analogue Converter), Decibels, in audio circuits, 8/4-5 PABXs, 34/4 19/11, 19/13-14, 19/15 Decoders see codes/coding Crosspolarisation efficiency, antenna, 17/9 DAMPS (Digital AMPS), cellphones, DECT (Digital European Cordless Crosstalk, 10/11, 30/7, 30/10 Telephony), 34/15-16, 49/4, 49/8-13 balanced pair cables, 15/5 DAR (Dynamic Alternative Routeing), DED (Dual Error Detection), 14/5 coaxial cables, 15/8 5/12-13, 54/14 Deep-sea cable, 15/8 digital transmissions, 28/6 DARPA (Defence Advanced Research Delay, PCM advantages, 19/4 Projects Agency), 16/19 distortion, 10/9 CS (Central Station), multipoint systems, DASS (Digital Access Signalling System), multiple access, 13/4, 13/7, 13/13 52/3-7, 52/7-8 ISDN, 44/12 propagation, 30/5, 30/9, 30/12 Index/6 Delay performance, single server queue, Digital systems, linear DMS-Core, 32/22-3 time-invariant, 2/10-13 DMS-Link, 32/23-4 Delay property, z-transforms, 2/13-14 Digital tandem (transit) exchanges, software, 32/23 Delta function, Dirac, 2/16-17 31/13-15 SuperNode, 32/19, 32/24 Demand assignment, multiple access, Digital telephones, 58/11 DMSUs (Digital Main Switching Units), 13/16-19 Digital transmission, 19/3-7 29/11 Demodulation see Modulation clocks, 28/12-16 DN (Directory Numbers), exchanges, 32/4 Demon (Maxwell's), 4/5 codes, 28/9-11 DN (Distinguishing Name), OSI, 16/14 Denmark, paging frequencies, 45/4 error performance, 28/5-9, 30/7-8 DNHR (