Computer Glossary
Packet filters: security method that filter by IP address; not adequate security for a network
Packets: data structures that collectively represent the transmission stream (headers and data); associated with the network layer when the communication protocol is connection-oriented
PAD (packet assembler/disassembler): assembles X25 packets on the sending end for transmission over the X25 PSDN, or disassembles X25 packets on the receiving end for onward transmission to the local network
Parallel port: port where the bits travel down parallel paths, arriving one byte at a time; can supply more bytes of data per unit time
Passive hubs: used in a LAN environment; special form of repeater that allow multiple devices to be wired into a central location and share the same media; do not regenerate (repeat) the signal
Path layer: layer of the OSI physical layer that is responsible for reliable end-to-end transport and payload delivery, including automatic recovery from failure points
PBX (private branch exchange): a telephone exchange that serves a particular business or office
PC (personal computer): a microcomputer whose price, size, and capabilities make it useful for individuals
PCI (peripheral component interconnect): a computer bus for attaching peripheral devices to a computer motherboard
PCM (pulse code modulation): process for converting from analog to digital
PDA (personal digital assistant): hand-held computer with a touch screen
PDU (protocol data unit): information that is delivered as a unit among peer entities of a network; in layered systems, a unit of data that is specified in a protocol of a given layer
Phase: where in the wave cycle the wave currently is; measured in degrees
Peer-to-peer networks: network in which each computer is capable of functioning as a client and a server; users on the network can freely share resources on their computer or access shared resources on other computers
Photonic layer: layer of the OSI physical layer that specifies fiber cable with optical light sources and receivers
Physical segmentation devices: divide collision domains to improve network performance
Ping: sonar concept implemented with the Echo Request and Echo Reply application; basic connectivity test between two TCP/IP network devices
POP (Post Office Protocol): how clients access their mailboxes on the messaging server; usually done in its third version, POP3
POPs (points of presence): an artificial demarcation point or interface point between communications entities
POST (power-on self-test): the pre-boot sequence for a computer, router, or printer
POTS (plain old telephone service): standard telephone service, the basic form of residential and small business telephone service
PRI (primary rate interface): an integrated services digital network (ISDN) configuration, usually intended for large users (see also BRI)
Process and application layer: Part of the TCP/IP model that performs the same functions as the application, presentation, and session layers of the OSI model
Processor: brain of the computer system where calculations and decisions are made; also referred to as the CPU
Processor memory: referred to as the L1 (level 1), an interface between the processor and the cache
Protocol: set of rules used to control the exchange of information that is understood by the transmitter and receivers
Proxy server: sits between the network router and the Internet; talks to the Internet on behalf of a network’s resources, allowing real network addresses to be hidden
PSDN (packet-switched data network): a publicly available network supporting packet-switched data, separate from PSTN
PSTN (public switched telephone network): the network of the world’s public circuit-switched telephone networks; in much the same way the Internet is the network of the worlds’ public IP-based packet switched networks
PU (physical unit): a value or magnitude conventionally adopted as a unit or standard of physical measurements (e.g., length, mass, and time); identifies a network node that supports communication sessions between logical units (LU) which represent end users in IBM's SNA
Pure play: newly developed business built on advantages afforded by e-commerce
PVCs (permanent virtual circuits): use a real, shared circuit in the service provider’s backbone
QoS (quality of service): the capability of a network to provide better service to selected network traffic over various technologies
RAM (random access memory): chips capable of storing and later dumping data in preparation for other uses
RARP (reverse address resolution protocol): protocol used to resolve an IP address from a given hardware address (e.g., an Ethernet address)
RAS (remote access service): allows users to access the network through dial-up modem connections
Receiver: destination of the message or data
Recovery routine: enables a computer to resume operation after encountering a problem, such as a power outage or program error
Remote login: allows a user at one computer to interact with another, as if the user’s computer is directly attached to the remote computer
Removable storage: a way to store information on disks that can be removed and used on different systems; most removable drives (also known as floppy drives) use a hard 3.5 inch disk
Repeaters: regenerate and reshape digital pulses and allow a signal to be transmitted further than a single circuit can achieve
RIP (routing information protocol): used by routers connecting LANs to exchange routing table information to determine the best path through the network at any point in time
ROM (read-only memory): chips that store data that needs to be maintained constantly
Routers: basic piece of network hardware necessary to connect one network to another; makes decisions about packet forwarding based on IP address information in the packet; directs traffic between network segments
RTMP (routing table maintenance protocol): a communication protocol used by AppleTalk to ensure that all routers on the network have consistent routing information