 numerical aperture negative acknowledgment North American Numbering Plan new data flag near-end crosstalk noise figure nautical mile; nanometer network management network-network interface or network-node interface numbering plan area network parameter control normal response mode; network resource management nonreturn to zero network services signaling data unit nanosecond(s) national signaling point network termination National Television System Committee ACRONYMS AND ABBREVIATIONS OAM, OA&M operations and maintenance; operations, administration, and maintenance optical carrier (OC-1, OC-3) overall loudness rating originating point code overall reference equivalent open system interconnection power amplifier private automatic branch exchange personal access communication services packet assembler-disassembler phase-alternation line pulse amplitude modulation positive acknowledgment with retransmission private branch exchange personal computer printed circuit board protocol control information pulse code modulation personal communication services; physical coding sublayer plesiochronous digital hierarchy public data network protocol data unit picture element poll-final picofarad packet handling personal handyphone system refers to the physical layer (OSI layer 1) p-intrinsic-n PIXEL picture element (same as pel) physical layer convergence protocol physical layer signaling phase modulation; physical medium physical medium attachment physical layer medium dependent pseudonoise path overhead POP/POT point of presence, point of termination point of sale plain old telephone service primary service (ISDN) primary reference source phase shift keying public switched network PSPDN packet-switched public data network PSPDS packet-switched data transmission service public switched telecommunication network payload type indicator (identifier) ACRONYMS AND ABBREVIATIONS permanent virtual circuit picowatt(s) picowatt(s) psophometrically weighted quadrature amplitude modulation quality of service quadrature phase shift keying