deo services to customers of all classes via power transmission and distribution lines. Current technologies offer speeds ranging from 1Mbps to 45Mbps. Also known as powerline communications (PLC) and broadband over powerlines (BPL). PM (phase modulation) A way to modify a sine wave signal to make it carry information. The sine wave, or carrier, has its phase changed in accordance with the information to be transmitted. PNAP (private network access point) A private point of access to the Internet, also called a peering point, that bypasses public NAPs. PoC (Push-to-Talk over Cellular) An open standard for push-to-talk (i.e., walkie-talkie) technology that defines how push-to-talk can be deployed over a cellular operator's packet data network using VoIP. PoC uses VoIP technology to stream voice over data networks such as GPRS. The key to PoC is IMS. point-to-point line A circuit that connects two points directly, where there are generally no intermediate processing nodes, although there could be switching facilities. Synonymous with two-point and always-on. policy-based management A system in which information about individual users, groups, organizational units, and entire organizations, as well as events (e.g., the beginning of the accounting department's month-end closing), can be associated with various network services or classes of service. polling A host-system-controlled method for determining whether each of the stations on a communication line has data to send. (passive optical network) A network in which one access line is shared among mul- tiple buildings. Optical splitters and couplers are used at each fiber connection in the network. POP (point of presence) The physical access location into a network. POP (Post Office Protocol) An application-layer protocol that e-mail clients use to retrieve e-mail from a remote server over a TCP/IP connection. port (1) A point of access into a communications switch, a computer, a network, or another electronic device. (2) The physical or electrical interface throug