电信专业英英词典P-2（在线收听）

　　PPSN

　　public packet switched network

　　Premises Distribution System (PDS)

　　PDS is the transmission network inside a building or among a group of buildings, for example an office park or a campus. PDS is used in this book as a generic term although AT&T used it to describe a specific product offering. The PDS connects desktop and other station equipment with common host equipment, (e.g., switches, computers and building automation systems), and to external telecommunications networks.

　　Private Branch Exchange (PBX)

　　A PBX is a premises switching system, serving a commercial or government organization, and usually located on that organization's premises. PBXs provide telecommunications services on the premises or campus, (e.g., internal calling and other services), and access to public and private telecommunications network services.

　　Private Network

　　A private network is a network made up of circuits and, sometimes, switching equipment, for the exclusive use of one organization.

　　PRI

　　primary rate interface

　　Protocols

　　Protocols are strict procedures for the initiation, maintenance and termination of data communications. Protocols define the syntax (arrangements, formats and patterns of bits and bytes) and the semantics (system control, information context or meaning of patterns of bits or bytes) of exchanged data, as well as numerous other characteristics (data rates, timing, etc.).

　　PSN

　　packet switched network

　　PSPDN

　　packet switched public data network

　　PSTN

　　public switched telecommunications network

　　PTT

　　postal, telephone, and telegraph

　　Public Switched Telephone Network (PSTN)

　　A Public Switched Telephone Network (PSTN) denotes those portions of the LEC and IXC networks that provide public switched telephone network services.

　　PUC

　　public utility commission

　　Pulse Code Modulation (PCM)

　　Pulse Code Modulation (PCM) is a modulation scheme involving conversion of a signal from analog to digital form by means of coding. See also modulation.