l odd (odd parity) or all even (even parity). parity check A procedure in which noninformation bits are added to data to make the num- ber of 1s in a grouping of bits either always even or always odd. This procedure allows detection of bit groupings that contain single errors. It can be applied to characters, blocks, or any specific bit grouping. Also called vertical redundancy check (VRC). passive optical splitter A device used in a PON that splits the power of the optical signal and distributes it to multiple customers and in the reverse direction combines multiple light streams onto a single fiber. Passive optical splitters don't need any power, hence the term passive; they work like a prism, splitting light into the colors of the rainbow. This means that a passive optical splitter is not sensitive to temperature or other elements that would be problematic for electrical components. Optical splitters can be located in a telco building, outside plant, or any other building along the fiber route. password A word or set of characters that must be given to satisfy security needs. patch panel A passive wiring device that facilitates manual patching of end-user machines onto ports on one or more network hubs. path (1) In a network, any route between any two nodes. (2) The route traversed by the infor- mation exchanged between two attaching devices in a network. Glossary Pbps (petabits per second) Pbps (petabits per second) 1,000Tbps. PBX (private branch exchange) A telephone switch located on a customer's premises that primarily establishes voice-grade circuits between individual users (extensions) and the switched telephone network. Typically, the PBX also provides switching within a customer's premises and usually offers numerous other enhanced features, such as least-cost routing and call-detail recording. Also called a PABX. PCM (Pulse Code Modulation) A scheme used to convert an analog voice signal into digital bitstream for transmission. PCM is a digital transmission technique that involves sam- pling of an an