Also known as a mediation device. A device that acts as a protocol converter to interface a high-performance third-party electronic station set to a Centrex system. Centrex systems are designed to support either generic, featureless station equipment or feature-rich proprietary station sets known as Pphones. Third-party electronic station sets can offer the same (or better) performance as P-phones but require a set handler to resolve proprietary signaling and control protocols. See also Centrex, protocol, and signaling and control.