| Term |
Definition |
| PA |
Power Amplifier. |
| PABX |
Private Automated Branch Exchanges. |
| Packet |
The "data" unit carried on a link layer. A packet, on an IP network, consists of an entire IP datagram or a fragment of a datagram. |
| Packet Assembly/Disassembly |
A function which creates packets from streams of data elements so that they can be transmitted through a packet switched network and replaces them in their original form at the final receiving point. |
| Packet Buffer |
A small memory used to store packets before, during and after transmission. |
| Packet Mode Terminal |
A terminal device which can receive and transmit packets of data operating in a packet switched network. |
| Packet Switched Data Network |
A network in which data is transmitted and routed in a specified grouping called a packet. CCITT X.25 specifications define the format and procedures for the major type of public packet switched data network in general operation. |
| Packet Switched Exchange |
A term used in X.25 packet switched networks to describe an intermediate switching point or node. |
| Packet Switched Network |
A network where routing is chosen for individual portions (packets) of a message. The route followed by each packet during a transmission may or may not be the same. At each point in the network the next leg of the route will be chosen based on a specific algorithm. |
| Packetized Voice |
A form of digital voice transmission the utilizes discrete packets of information. Useful in T1 transmission systems and Integrated Service Digital Networks (ISDN). |
| PACNET |
A packet switched network implemented in Taiwan. |
| PAD |
Packet Assembler/Disassembler. |
| PAL |
Abbreviation for Phase Alternation by Line - Video standard used in Britain, other parts of Europe, and China. It has a higher definition and different screen format from the US NTSC standard. Running a television program written for PAL on an NTSC system can result in the bottom of the screen image being cut off. |
| PAM |
Pulse Amplitude Modulation. |
| PAMA |
Pulse address multiple access - In this case carriers are characterized by their temporal and special characteristics at the same time. |
| Parallel Interface |
The interface between a device (computer, terminals etc.) and the multiple transmission channels needed to support parallel transmission. |
| Parallel To Serial Conversion |
The process whereby parallel data which is carried on a computer's internal bus system is converted into a serial stream for transmission. |
| Parallel Transmission |
The process whereby binary bits are transmitted in groups. (8,16, 32 bits at a time requiring an appropriate number of conductors). Normally used when transferring data to high speed peripherals such as printers or disks. |
| Parity Bit |
The bit which is added to an encoded character to force the total summation of the bits to be either odd or even. |
| Parity Check |
The process whereby a single bit is added to an encoded character by the transmitting device to force the total sum of the bits to always be an odd number (odd parity) or always be an even number(even parity). The receiver can then check the oddness (or evenness) of the received value for error checking purposes. |
| Passive Optical Network |
A fiber-based transmission network containing no active electronics. |
| Passive Star |
The implementation of ring topology such that groups of connections are made via wiring boxes giving the appearance of a star configuration. Implemented to allow devices to be added to a ring without halting it's operation. |
| Path Length |
A term often used to describe the "logical" length of a connection path as opposed to the true physical length. The distance is described in terms of the number of hops (from device to device) in the path between source and destination. |
| PAX |
Private Automatic Exchange. |
| Payload |
48-byte segment of the ATM cell containing user data. Any adaptation of user data via the AAL will take place within the payload. |
| PBX |
Private branch exchange - A privately owned phone switching system used inside a business. |
| PCB |
Printed Circuit Board. |
| PCM |
Pulse Code Mulation - PCM is the basic method of encoding an analog voice signal into digital form using 8-bit samples. Defined by the ITU standard G.711. |
| PCM Binary Code |
A pulse code in which the quantized val-ues are identified by binary numbers taken in order. |
| PCM Multiplex Equipment |
Equipment for deriving a single digital signal at a defined digit rate from two or more analog channels by a combination of pulse code modulation and time division multiplexing (multiplexer) and also for carrying out the inverse function (demulti-plexer). The description should be preceded by the relevant equivalent binary digit rate, e.g., 2048 Kbit/s PCM multiplex equipment. |
| PCR |
Peak Cell Rate - A traffic parameter (in cells per second) that characterized the source and gives the maximum rate at which cells can be transmitted. It is calculated as the reciprocal of the minimum intercell interval (the time between two cells) over a given virtual connection (VC). |
| PCS |
Personal Communications Services - A two-way digital service for mobile voice, messaging, and data transmission regarded as the second generation of wireless service. |
| PCU |
Packet control unit - Network component that normally resides in a BSC and directs packet traffic to the SGSN for processing by the GPRS network. |
| PDIP |
Plastic Dual Inline Package. |
| PDN |
Packet data network - Represents a public or private packet-based network, such as an IP or X.25 network. |
| PDP |
Packet data protocol - Network protocol used by external packet data networks that communicate with a GPRS network. IP is an example of a PDP supported by GPRS. Refers to a set of information (such as a charging ID) that describes a mobile wireless service call or session, which is used by mobile stations and GSNs in a GPRS network to identify the session. |
| PDV |
Packet Delay Variation - RTP packets arrive with a certain delay with respect to when they were sent. PDV is a measure of how much that delay varies on an xxPCM channel. PDV measures the peak-to-peak packet delay throughout the network. PDV is only relevant on CBR connections. |
| Peak Limiting |
In PCM, the effect caused by the application to an encoder of an input signal whose value exceeds the virtual decision values of the encoder. |
| Peak Traffic |
The maximum traffic flows (data bits or characters per unit time ) in a predefined period of time. Maximum data rate in characters per second in any twenty four hour period, for example. |
| PEC |
Photoelectric Cell. |
| Peer Protocol |
The set of rules defining the procedures for communication between like entities. The identical entities may be devices or software modules at specific layers in a layered network architecture implementation. |
| Penetration Tap |
A connection method used in Ethernet installations which allows for the connection of devices to the cable without interrupting network operation. A sharp, pointed probe is used to penetrate the outer insulation and grounding shield of the co-axial cable and make direct contact with the inner conductor. |
| Persistence |
When used in a LAN access method describes the probability that when a device sees a free transmission line it will attempt to transmit. 1.0 persistence indicates that the probability is 100% that is that it will always attempt to transmit. |
| PF |
Pulse Frequency. |
| PFM |
Pulse Frequency Modulation. |
| PG |
Power Gain. |
| PGL |
Peer Group Leader - ATM switch within a PNNI peer group, which summarizes reachability within the group and sends this information up the routing hierarchy. |
| Phase |
The relative timing of an alternating signal. |
| Phase Adjust |
This is a term used to describe a method of adjusting the hue in a NTSC video signal. The phase of the color subcarrier is moved, or adjusted, relative to the color burst. PAL and SECAM systems do not usually have a phase (or hue) adjust control. |
| Phase Hit |
In telephony the unwanted and significant change in the phase of a modulated analog signal caused by external factors. |
| Phase Jitter |
The unwanted shortening or lengthening of cycles in an analog signal resulting in distortion and possible error. |
| Phase Roll |
Variations in the phase of a transmitted signal and it's echoed back modem verification. Most often encountered in international systems. |
| Phase Shift Modulation |
The process whereby the phase angle of an analog signal is varied to carry digital information. The most popular method used by common carriers in high speed data transmission systems. |
| Phase Slope |
The rate at which a given signal changes phase with respect to an ideal signal. It is measured in seconds per second. |
| Photo-bleaching |
A reduction in added loss that occurs when a fiber is exposed to light. Ionizing radiation causes added loss. This loss can be reduced by transmitting light through the fiber as during normal operation or by exposing the fiber to sunlight. |
| Photocurrent |
The current that flows through a photosensitive device, such as a photodiode, when exposed to light. |
| Photo-darlington |
A light detector in which a photo-transistor is combined in a circuit with a second transistor in order to amplify its output. Not known for speed but for sensitivity. |
| Photodetector |
Used on the receiving end of a fiber optic cable to convert light energy into electrical energy. |
| Photonic Layer |
The lowest of the four layers of SONET which specified which type and sensitivity of fiber and laser must be used. |
| PHY |
Physical layer. |
| Physical Address |
A set of numbers (or other unique identifier) which denotes a specific piece of hardware. |
| Physical Layer |
The layer in a layered network architecture, such as the ISO OSI seven level structure for example, which is responsible for the actual transmission of bits across a medium. |
| Physical Layer Signaling |
The electrical methodology used to transfer information from a transmission interface to the communications channel. |
| Physical Level Relay |
Another name for a repeater. |
| Piggybacking |
A (used at the data link layer or the transport layer in a layer network architecture) methodology which allows for transmission acknowledgments to be carried in transmission frames being received from the destination. |
| Pin-diode |
A photodetector used to convert optical signals to electrical signals in a receiver. |
| Pipelining |
A (used at the transport layer or the data link layer in a layer network architecture) methodology which allows for the transmission of multiple frames without waiting to see if they are acknowledged on an individual basis. Each frame may have to be acknowledged later and in sequence or a process of implied acknowledgment may be employed. Implied acknowledgment is a process whereby negative acknowledgment of a specific frame implies that all previously transmitted frames have been received correctly. |
| PIV |
Peak Inverse Voltage. |
| Plastic Fiber |
An optical fiber made of plastic rather than glass. |
| Plesiochronous |
Two signals are Plesiochronous if their corresponding significant instants occur at nominally the same rate, any variation in rate being constrained within specific limits. |
| PLIM |
Physical layer interface module - Interface that allows the AIP (ATM Interface Processor) to a variety of physical layers, including TAXI and SONET multimode fiber-optic cable, SDH/SONET single-mode fiber cable, and E3 coaxial cable. |
| PLL |
Phase Lock Loop - A phase lock loop is a component that generates an output clock by synchronizing itself to an input clock. |
| PNNI |
Private Network-Network Interface - The interswitch interface within a private ATM domain. The PNNI trunking protocol providing for hierarchical ATM-layer routing and QoS support. |
| POF |
Plastic Optical Fiber. |
| POFFDI |
Plastic Optical Fiber/Fiber Distributed Interface. |
| PON |
Passive Optical Network. |
| Poor Man's Routing |
A facility used in many packet switched networks to allow a source node pre-define the routing to be taken to the destination by-passing the normal routing algorithm implemented at the network layer. |
| Port |
An interface of a computer or other transmission device which acts as an input or output (or both) point. |
| POS |
Packet Over SONET - A means of transporting packets over a SONET link with minimal overhead in a point-to-point connection. POS uses PPP as its link protocol. |
| POS-PHY |
A bus standard for connectiing Packet Over SONET link layer devices to PHYsical layer ones. POS-PHY level 2 was based loosely on UTOPIA level 2. |
| POTS |
Plain Old Telephone Service - The ubiquitous, 64 kbps phone service widely deployed in today's phone networks. |
| Power Line Carrier System |
A LAN method which utilizes the existing power distribution cables (110 volt 60 cycle, etc.) within a building thus eliminating the need for special cable installation. |
| PPP |
Point-to-Point Protocol - A link protocol that allows for transport of many network protocols over a point-to-point link. PPP has very little overhead (1 or 2 bytes per packet), making it very attractive for some applications. |
| PRA |
Primary Rate Access. |
| Preamble |
A pattern of bits transmitted at the start of a transmission frame used to implement transmitter and receiver synchronization. |
| PRI |
Primary Rate Interface - In Integrated Service Digital Network technology the device used to connect a PBX (for example) to the transmission network. The interface (in the USA) connects 23 64 kilo bit per second B channels and one 64 kilo bit per second D channel. |
| Private Branch Exchange |
The switching point controlling connection and transfer between all internal telephone extensions and between any internal extension and external trunks. |
| Process switching |
Operation that provides full route evaluation and per-packet load balancing across parallel WAN links. Involves the transmission of entire frames to the router CPU, where they are repackaged for delivery to or from a WAN interface, with the router making a route selection for each packet. Process switching is the most resource-intensive switching operation that the CPU can perform |
| PROM |
Programmable Read-Only Memory. |
| Protocol |
A formal set of conventions governing the format and relative timing of message exchange between to communicating objects. A formal statement of the proce-dures that are adopted to ensure communication between two or more functions within the same layer of a hierarchy of functions. |
| PSDN |
Packet Switched Data Network. |
| Pull-In Range |
The input frequency range over which the PLL must be able to pull into synchronization. |
| Pulse |
An abrupt, short duration, change in energy from one state to another and back. Normally used to convey information. |
| Pulse Amplitude Modulation |
Amplitude modulation of a carrier which uses pulses of varying energy level (amplitude) to transmit information from source to destination. |
| Pulse Code |
A code giving the equivalence between the quantized value of a sample and the corresponding character signal. |
| Pulse Code Modulation |
A process in which an analog signal is sampled, and the magnitude of each sample with respect to a fixed reference is quantized and converted by coding to a digital signal. |
| Pulse Duration Modulation |
A method of carrying digital information by varying the duration of fixed frequency pulses. |
| Pulse Position Modulation |
A method of carrying digital information by varying the position in time of fixed frequency pulses. The time duration of the pulses is not varied. |
| Pulse Width Modulation |
The method of carrying digital information on variable width pulses of a single analog frequency. May also be referred to as pulse duration modulation. |
| Px64 |
This is basically the same as H.261. The term is starting to fade away since H.261 is used in applications other than ISDN video conferencing. |
