Telecom Dictionary

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P-MAC 
packet media access controller

PAD 
packet assembler-disassembler

PCB 
printed circuit board

PDS 
premises distribution system

Personal Communications
Personal communications provides at least one human operator with direct terminal access and 
real time or near real time interactive communications with a remote human opera tor or an 
information system resource. Personal communications can refer to a broad range of services, 
systems and equipment, e.g., facsimile machines, landline telephones, cellular tele phone 
systems and emerging personal communication system (PCS) adjuncts, and a variety of radio 
systems including pagers, hand-held remote data entry terminals, and autonomous citizen-band-
like radio systems.

PHY 
physical-layer protocol

PMD 
physical-layer media-dependent

Point-of-presence (POP)
A POP is a physical location within a LATA that an IXC establishes for the purpose of gaining 
access to BOC/LEC networks within the LATA using LEC provided access services. An IXC may 
have more than one POP within a LATA and the POP may support public and private, switched 
and non switched services.

POP 
point-of-presence

POT 
point of termination

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.

PVC 
permanent virtual circuit