defined, 108 collision detection, 288-91 illustrated, 109 contention algorithm, 289 use, 109 defined, 284 See also Speech-coding methods network structure, 284-85 Digital operation, 288-89 broadcast systems, 359-60 CW modulation, 129, 149 messages, 89-90 Cyclic redundancy check (CRC), 161, 162, signals, 85-86 Digital cellular system at 1,800 MHz (DCS-1800), 204 compression, 266-67 Digital cross-connect equipment (DXC), loss tolerance, 79 45, 178 rate, 78-79 Digital enhanced cordless telecommunica- Data circuit-terminating equipment tions (DECT), 111, 198 (DCE), 239 Digital milliwatt, 118-19 Data communication protocols, 248-62 data sequence for, 120 hierarchies, 248-50 defined, 118 layering, 250-51 for European PCM, 119 Data communications, 237-355 illustrated, 119 asynchronous and synchronous, 239-42 reference level generated by, 118 circuit-switched, 243 Digital subscriber line. See DSL packet-switched, 243-45 Digital systems principles, 237-42 advantages, 86 serial and parallel, 238-39 binary signals, 86 Data communications network (DCN), multiplexing, 88 61-62 S/N ratio, 157, 158 illustrated, 62 software control of, 88 planning, 61 Digital-to-analog conversion (D/A), 92 redundant routes to, 62 Digital TV, 7 sets, 360 See also Network management Data link layer, 254-55 standards, 260 defined, 154 Digital video broadcasting (DVB), 138 frame, 261 Discrete multitone (DMT) modulation, protocol examples, 254-55 See also OSI reference model Distortion, 127 Data terminal equipment (DTE), 239 Distributed feedback (DFB) lasers, 180 Decibels, 115-16 Distributed intelligence, 53-54 Decoding, 151 Distribution frames, 43-45 Dense wavelength division multiplexing digital (DDF), 44-45 (DWDM), 141 main (MDF), 43-44 Dialing optical (ODF), 44 abbreviated, 54 DM, 109 rotary, 25-26 Domain Name System (DNS), 328-30 defined, 328 tone, 26-28 Dial-up modems, 267 hierarchy, 329 Index implementation, 329 European Committee for Electrotechnical servers, 330 Standardization/European Com- DSL, 269-77 mittee for Standardization application