. See also digital networks; frame relay; holdover and slip performance, 141 local networks; long-distance network design; synchronization plan stratum levels, 140-141 network synchronization North American Numbering Plan (NANP), 6 grade of service for, 58 North American PCM standard, 108, 109, 114 automatic line build-out, 121 north pole, 586 lifespan of, 345 notation, 603-604 line build-out, 103 Notify command, 400 multilevel, 545f NPA (numbering plan area) codes, 6 packet-switched, 318 NRZ (nonreturn-to-zero) coding, 263-264, 265 size of, 8 NTM center, 548-549 structure of, 137 null context, 398 network synchronization, 137-139 numbering methods of, 139-141 effects on signaling, 161-162 network time bases, 540 trunk, 9 network topologies, 10-13, 181 numbering capacity, theoretical, 6 hierarchical network rules, 11-12 numbering plan areas (NPAs), in long-distance trend away from hierarchical structure, 13 network design, 175 network traffic management (NTM). See also NTM Nyquist bandwidth, 271 center Nyquist rate, 447 controls on, 551-553 Nyquist sampling theorem, 108-109 functions of, 550-551 principles of, 549 OC-N electrical signals, 490, 493, 500-501 network troubleshooting, 542-544 octets, 387, 388, 490 rapid, 542 odd parity, 255 network utilization, in troubleshooting, 543 Oersted, Hans Christian, 20 neutral dc transmission, 258-259 off-contour loss, 226 neutral transmission, 264f, 2655 offered traffic, 56, 61 Newbridge network monitoring equipment, off-hook condition, 4, 68, 92, 95 545-546 minimum loop current during, 96 19H66 cable, 98 office, 11 nodes, 3 ohm, 34, 35 noise, 48-51, 626, 627-628 Ohm's law, 577-580 crosstalk, 50-51 in ac circuits, 597-599 in data transmission, 269-271 Okumura/Hata radio propagation model, 463-464 impulse, 50 one-frequency signaling, 151 intermodulation, 49-50 one-way circuits, 9-10 thermal, 48-49 on-hook condition, 68, 92 noise accumulation, in FDM systems, 85 open systems interconnection (OSI), 280-284 noise advantage, 629 LAN protocols and, 295-297 noise figure (NF), 206