Data transfer mechanism in which data is disassembled into small pieces, called packets, before transmission. Each packet consists of header and payload. Header contains source and destination addresses and control bits, while payload contains a piece of data. At the receiving end, all packets are assembled into the original data based on header information.
Unlike circuit-switching, packet switching lets multiple users share a transmission channel resulting in better bandwidth utilization.
See picture.  Compare with circuit switching and cell switching.

A palm sized computer.

Personal Area Network. A network that connects computers, peripherals, and mobile devices that are located within a personal operating space (e.g. desk, car, room).
See picture. Also see POS, LAN, MAN, WAN.

Password Authentication Protocol. An authentication protocol that allows a client to log on to an ISP using username and password. Username and password are sent from a client (subscriber) computer to the ISP's network access server (NAS) and forwarded by the NAS to an authentication server without encryption.
PAP is still used with PPP even though there is a more secure authentication protocol, i.e. CHAP.
Also see PPP and CHAP.

A port in a computer where data is sent several bits at one time. Also known as LPT or printer port. The connector for parallel port is DB-25 female connector.
See picture. Also see serial port.

A PIN that is needed for two Bluetooth devices to pair. The passkey is temporary for a session. It can stay the same or change based on user preference. However, for security purpose it is better to always change the passkey especially when using a Bluetooth device in a public place.

A string of characters that is inputted when logging in to a computer, network, or specific application. Password is case sensitive and it can consist of letters, numbers, and symbols.

Private Branch Exchange. A device that functions as a telephone switch for a company's telephone network.

Personal Computer. Refers to desktop computer.

Peripheral Component Interconnect. PCI expansion slots are used for adding functions to a computer. Modem and network adapter are common expansion cards that are inserted into PCI slots.
While mini PCI is a PCI slot with smaller form factor that's found on notebooks.

Pulse Code Modulation. A type of modulation that is used in analog to digital conversion.

Personal Computer Memory Card International Association. PCMCIA card (a.k.a. PC Card) is a board having the size of a credit card (but thicker) that is used for connecting a notebook to a network (LAN/WAN/Internet).

Personal Communication Service.

Personal Digital Assistance. Portable computer with limited processor, memory, storage, and programs to support frequently used applications.

Plesiochronous Digital Hierarchy. Refers to a hierarchy of non-synchronous transmission rates, that includes 2/8/34/140 Mbps (ETSI) or 1.5/6/45 Mbps (ANSI).
PDH had been the transport standard for years but it has been replaced by SDH/SONET. However, its installed base is still large.
Also see E1, T1, SDH, and SONET.

Protocol Data Unit. Data packet is transmitted in PDU across the OSI higher layers (i.e. Transport, Session, Presentation, and Application Layers).
Also see OSI model.

Mouse, keyboard, speaker, printer, or any device that can be connected to a computer, controlled by the computer, and in some cases powered by the computer.

A type of spam that tries to fool Internet users to supply confidential information to the spammer. The typical form of phishing is an e-mail, that looks legal and official and comes from an e-mail address that represents a bank or other established institutions, asking the would-be victim (recipient) to input her personal details for account confirmation purpose. The e-mail usually contains genuine logo of the bank and adopts the theme style used in the bank website.

Network technology that uses phoneline as physical medium to connect computers and devices. It occupies higher frequencies in the phoneline spectrum so telephone connection is not disturbed by the presence of the phoneline network.
Also see HomePNA and powerline network.

Physical medium characteristics of a network technology.

Layer 1 in the OSI model. The Physical Layer concerns with how a connection is set up in the physical medium of a network. It specifies physical and electrical characteristics of the network, i.e. cable, connector, voltage level, and signaling. RS-232, UTP, coaxial cable, fiber optic operate at the Physical Layer.
The Physical Layer handles information in binary digit (bit). It converts electrical signals into bits and vice versa.
Also see OSI model.

A network of Bluetooth devices with a controlling device as a host (master) and up to seven devices as peripherals (slaves). All Bluetooth devices participating in a piconet shares a common channel.
Also see Bluetooth and scatternet.

Personal Information Management. PIM data includes address book and calendar.

Personal Identification Number. A secret number that is assigned by a service provider and usually can be changed later by its user.

Packet INternet Groper. A DOS command that is used to test whether a particular node or IP address is online. 

Public Key Infrastructure. A security scheme that uses digital certificate issued by a Certificate Authority to authenticate entities or individuals over the Internet.

Public Land Mobile Network. Refers to mobile telephone network that consists of interconnecting mobile switching centers and base stations.
Compare with PSTN.

A device or peripheral capability to be automatically detected and configured by the Operating System when it is plugged to a computer. Often abbreviated to PnP.

Phase Modulation. A modulation technique in which the carrier phase changes according to the baseband signal (information) variations.
Also see modulation.

Power over Ethernet. A technology that enables an Ethernet cable to carry power (electricity) in addition to data. Its purpose is to reduce the need for wires and improve network uptime (free from power outage). PoE consists of three components, i.e. the power sourcing device, the device to be powered, and the Ethernet cable. PoE is defined in IEEE 802.3af.
The development of PoE was first inspired by the increasing use of VoIP. Users want VoIP service to be uninterrupted by power outage, like POTS. Nowadays, PoE products experience an increase in use, especially for powering VoIP phone, wireless access point, and network camera.
Also see inline power, Ethernet, POTS, VoIP.

Passive Optical Network. An optical transmission system that carries signals from Central Office (CO) to the termination point (e.g. customer premises in FTTP case) over fiber optic cable. It's called passive because once signal leaves the CO, it runs through fiber optic distribution network by means of connecting and splitting without active components or powered electronics. At the fiber optic termination point, the optical signal is converted back to electrical signal by an ONU (Optical Network Unit) or ONT (Optical Network Terminal).
Also see FTTP, APON, BPON, EPON, and GPON.

Point of Presence. An ISP's remote access server and other equipment put in a location near its subscribers' sites to enable access to the ISP using local calls instead of long distance calls.
Also see ISP.

Post Office Protocol 3. A standard protocol that is used to retrieve (download) e-mails from a mail server. If you have an account from a mail service provider that offers POP3, with simple setting you can access and read your e-mails from your favorite mail clients like Outlook Express, Eudora, mobile phone mail client.
Compare with IMAP.

A connection point on a computer that is used for connecting peripherals, e.g. serial (COM) port and parallel (LPT/printer) port. Or a virtual connection point (a memory allocation) to run certain applications in a server, e.g. FTP (port 21), SMTP (port 25), and HTTP (port 80).

A function in a router that enables access from the Internet or other networks to services (e.g. FTP, HTTP, SMTP) provided by a computer in an internal network. The serving computer remains anonymous because the access is directed to the router address at a specific port. Access to this port is forwarded by the router - according to a predefined setting- to the intended port in the serving computer.

Point of Sales, the spot in a store where every transaction takes place OR Personal Operating Space, a space about a person or object that typically extends up to 10 meters in all directions and envelops the person whether stationary or in motion..
Also see PAN.

Plain Old Telephone Service. Refers to the legacy fixed telephone service that is served by a telephone switch (Local Exchange). The term is often mentioned in comparison to new telephone technologies, such as VoIP, VoDSL, VoATM.
Also see PSTN.

A network technology that uses powerline as physical medium to connect computers and devices. It occupies higher frequencies in the powerline spectrum, so it doesn't interfere with electric currents.
Also see HomePlug and phoneline network.

Point-to-Point Protocol. A standard protocol that is used in dial-up Internet access to connect a subscriber modem to her ISP's modem. PPP provides authentication, encryption, and compression.
PPP is a Layer 2 protocol, it can encapsulate Layer 3 protocols such as IP and IPX.
Also see PAP, CHAP, EAP.

PPP over ATM. A standard protocol for encapsulating PPP frames in AAL5 (ATM Adaptation Layer 5).  PPPoA is used in broadband Internet connection, using ADSL or cable modem.
Also see DSL and cable modem.

PPP over Ethernet. A standard protocol for encapsulating PPP frames in Ethernet frames.  PPPoE is used in broadband Internet connection, using DSL or cable modem. It provides log-in authentication using username and password.
Also see DSL and cable modem.

Point-to-Point Tunneling Protocol. A protocol developed by Microsoft that enables PPP tunneling (that is encapsulation and encryption of PPP session) over the Internet.
Also see VPN.

The 62-bit synchronization information of an Ethernet frame. Preamble precedes other bits in an Ethernet frame.
Also see frame.

Layer 6 in the OSI model. The Presentation Layer performs data format translation, data compression to efficiently use network resources, and data encryption to ensure that data is received only by the intended receiver.
Also see OSI model.

Primary Rate Interface. An ISDN circuit that has E1 or T1 capacity. E1 rate, used in Europe, is given by 30 B channels and 1 D channel. T1 rate, used in North America and Japan, is given by 23 B channels and 1 D channel.
Also see E1, T1, ISDN, B channel, and D channel. Compare with BRI.

A network device that connects printers to a LAN.

A range of IP addresses that can be assigned to any node in a network for internal network connection.
Contrast with public IP address.

A network that belongs to a person, a company, or an organization that has access restriction, thus can be accessed only by authorized parties.
Contrast with public network.

A set of rules that are defined to enable communication between computers or devices over a network. A proprietary protocol is defined by a networking product manufacturer and used only between its own products. A standard protocol is defined by an international standard body or an industry association and used between any products that conform to the standard.

A computer or a server that represents other computers on the Internet.

Phase Shift Keying. A modulation technique in which the phase (angle) of a carrier wave is changed according to the baseband signal (information) variations.
Also see modulation.

Public Switch Telephone Network. Refers to the fixed telephone network that is served by interconnected exchanges (local exchange, regional exchange, international exchange). An exchange is a telephone switch that functions to establish, maintain, and terminate telephone connections.
Compare with PLMN.

A range of IP addresses that can be assigned to any node in a network for internal network connection as well as Internet connection.
Contrast with private IP address.

A network that doesn't have access restriction, thus can be accessed by anyone. Internet is the biggest public network that has worldwide coverage.
Contrast with private network.