Index - A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z
PACKET - In the sense of communications, a structured group of binary digits in a prearranged sequence containing synchronism, address, control an error- checking data. Specialized synonym for a "block" of data in CCITT Packet Data Network standards.
PACKET SWITCHED NETWORK - A network dedicated to the routing and delivery of data put in the form of standardized "packets."
PACKET SWITCHING - The technique in which a stream of data is broken into standardized units called "packets," each of which contains address, sequence, control, size and error checking information in addition to the user data. Specialized packet switches operate on this added information to move the packets to their destination in the proper sequence and again present them in a contiguous stream. Compare: Circuit Switching; Message Switching.
PAD - 1.) An attenuator deliberately placed in a transmission channel to cause transmission loss; 2.) Contraction of the term Packet Assembler/Disassembler in Packet Switched networks, the instrumentality that converts user data between steady streams and packets.
PAD CHARACTER/FILL CHARACTER - A control character inserted into data fields when insufficient characters are supplied to fill the data block or the block is incomplete. Interesting to note that a common "pad" character is hex 7F, equating to ASCII "Delete," the same as TWX "rubout" and Baudot "Letter Shift," all essentially the same in every generation of data communications.
PARALLEL TRANSMISSION - Simultaneous transmission of all parts of a signal at one time; in data transmission, requiring a separate signal path for each of the bits of a character; internal to computers, this is called a "parallel bus."
PARITY - a constant state of equality; one of the oldest and simplest methods of error checking data transmission. Characters are forced into parity (total number of marking bits odd or even as selected by choice) by adding a one or zero bit as appropriate when transmitted; parity is then checked as odd or even at the receiver.
PARITY BIT - a check bit appended to an array of binary digits to make the sum of all the digits always odd or always even.
PARITY CHECK - a checking method that determines if the sum of all the digits in an array is odd or even.
PATCH - 1.) a temporary electrical wiring change, usually made with plugs and jacks; 2.) making an improvised modification, to change a computer software routine in a rough or expedient way.
PHYSICAL LAYER - Layer 1 within the OSI Reference Model for Open Systems Interconnection; providing electrical, mechanical and handshaking procedures for transmission. Example: RS-232 is a Layer One function.
POINT OF PRESENCE (POP) - A physical location within a LATA at which an IEC establishes itself and an end point of its network for the purpose of obtaining LATA access and to which the LEC provides access services.
POINT-TO-POINT - A communications circuit between two terminations only. Contrast with Multipoint.
POLAR KEYING/POLAR SIGNALING - A technique in current loop signaling that uses opposite polarities for the two binary states. Tends to provide longer range and suffer less interference than do simpler single-polarity methods. Synonyms: Bipolar; Double Current. Antonyms: Unipolar; Neutral; Single Current.
PORT - Entrance or access point to a computer, multiplexor device or network where signals may be supplied, extracted or observed.
POST TELEPHONE AND TELEGRAPH (PTT) - Foreign government agencies responsible for regulating communications, having the voting status of "Administrations" in the ITU charter Privately-owned entities such as AT&T or MCI are "Recognized Private Operating Agencies, but have only an influence on the vote of their "Administration;" in the U.S. structure, the "Administration" is the Department of State of the U.S.
PREGROUP - Now obsolete term used in certain non-Bell carrier terminal equipments to form up sets of 3 channels for placement into a basic carrier group of 12 channels.
PRESENTATION LAYER - In the OSI Reference Model, the next- to-topmost layer that provides services to the user- interfaced Application Layer. The Presentation Layer is where messages to be transmitted are grouped, formed, converted to and from serial to parallel and undergo conversion between computer and communications codes.
PRIMARY AREA - A customer's local telephone calling area.
PRIMARY INTEREXCHANGE CARRIER (PIC) - The IEC designated by a customer to provide inter-LATA service automatically when the customer dials 1+ an area code and number. Synonym : Default Carrier.
PRIMARY ROUTING POINT - The switch designated as the control point for a long haul telephone call.
PRIVATE BRANCH EXCHANGE (PBX) - A private phone system (switch) used by medium and large companies connected to the local public switched telephone network (LEC), performing a variety of in-house routing and switching. Users usually dial "9" to get outside the PBX to the local lines (in North America).
PRIVATE LINE (PL) - A full-time leased line directly connecting two or more points, used solely by purchaser. The most common form is a tie line connecting two pieces of a user's own phone equipment - flat rate billing, not usage sensitive. Synonyms: Dedicated Line; Leased Line.
PRIVATE USE NETWORK - Two or more private line channels contracted for by a customer and restricted for use by that customer only.
PROCESSING DELAY - In data communications, the time taken by a computer to operate on an inbound message and return a response; frequently not accounted for in complaints of telecommunications response time problems.
PROPAGATION DELAY/PROPAGATION TIME - The time period between injecting a signal into a communications channel and its exit at the distant end. While not generally significant to speech, propagation delay can be very restrictive to computers, particularly the long delays on satellite channels and to a lesser extent even those between continents on submarine cable; the most common cause in these cases is the "stop-and-wait" nature of many pessimistic computer protocols, which are disappearing from the scene.
PROTECTOR/PROTECTOR BLOCK - Hardware interfacing devices used in telephone cable between inside and outside wire for the purpose of limiting voltages and/or currents to values safe for personnel and equipment.
PROTOCOL - A set of procedures for establishing and controlling the transmission of information. Examples: SDLC; Bisync.
PROTOCOL CONVERSION/PROTOCOL CONVERTER - Generic name and name of the devices that perform a widely variable set of conversions of code, speed, electrical interface and/or block formatting and error checking/correction in data circuits. Example: a packet network PAD operating between an ASCII terminal and a packet network is a form of protocol converter. When the function is to make the line signals of a particular terminal appear like another, the protocol converter is a type called a Terminal Emulator.
PUBLIC SWITCHED NETWORK (PSN) - The pre-Divestiture nationwide network maintained by AT&T and the local telephone companies that provided nationwide telephone service as a monolithic entity. PUBLIC UTILITY COMMISSION (PUC)/PUBLIC SERVICE COMMISSION (PSC) - The state commissions regulating intrastate communications; variations on the term abound.
PULSE - In communications, typically a signal characterized by a constant amplitude and duration; the line signal representation of a binary digit.
PULSE CODE MODULATION (PCM) - The form of digital transmission in which information for transmission is sampled at regular intervals and a series of pulses in coded form are transmitted representing the amplitude of the information signal at that time. The most common form of PCM in North America is one in which analog signals of less than 4 kilohertz are sampled 8,000 times per second and converted into an 8-bit code, resulting in 64 kilobits per second for transmission. Twenty-four of these streams are Time Division Multiplexed into a 1.544 megabit stream for T-1 transmission. The European equivalent is 30 channels in a 2.048 megabit stream.
PULSE-LINK REPEATER - Connects two E&M signaling circuits back to back, changing the E of one circuit to the M of the other and vice versa. PULSE MODULATION The modulation of a series of pulses to represent information-bearing signals. Typical methods involve modifying the amplitude (PAM), width (PWM), duration (PDM) or position (PPM). Pulse Code Modulation (PCM) is the most common modulation technique involved in telephone work.
PUSH BUTTON DIALING - Synonyms: Dual Tone Multi- Frequency; Touch-Tone (an AT&T service mark); Key Pulsing (on long distance operator positions).