BBN Technologies, founded by Richard Bolt, Leo Beranek, and Robert Newman in 1948, originally operated as an acoustical consulting firm. It contributed to the design of the United Nations' General Assembly Hall. It also developed suspended reflectors that improved the acoustics of concert halls. In 1952, the firm developed sound-stream mufflers for jet engines and building ventilation systems. BBN Technologies developed the Perceived Noise Decibel (PNdB) metric in 1958. In 1970, the company developed the TENEX virtual-memory operating system for Digital Equipment Corporation computers. It introduced the Private Line Interface (PLI) ARPANET message encryption technology in 1972. BBN Technologies also designed ARPANET Terminal Interface Message Processors (TIPs), the INTERLISP list processing programming language, and the Hear What I Mean (HWIM) speech recognition system technologies. Working with Stanford University and University College, London, the firm developed the first Internet routers in 1976. It introduced the T/20 high-performance packet router and the Dynamic Analysis and Replanning Tool (DART) in 1990. In 1997, BBN Technologies was inducted into the U.S. Space Foundation's Technology Hall of Fame. In the same year, it was acquired by GTE Corporation. The company won a Corporate Innovation Recognition award from the Institute of Electrical and Electronics Engineers (IEEE) in 1999. In 2000, GTE merged with Bell Atlantic, forming Verizon Communications. BBN Technologies now operates as a Verizon Communications subsidiary. It is based in Cambridge, Massachusetts.