ARQ-M, short for Automatic Repeat reQuest, Multiplex, is a radio telegraphy protocol used to reliably forward telex messages over partially reliable radio links. It is a low-speed system designed to match the performance of landline telex systems and allow those messages to be forwarded over long distances using shortwave radios. The first ARQ-M link was built in the Netherlands, and began exchanging messages with a counterpart in New York in 1947. ARQ-M is similar in concept to ARQ-E, but ARQ-E has no multiplex capability and uses a different 7-bit alphabet. History The telex system, which developed out of the telegraph system, is based on defined electric current levels that are interpreted as a mark or space signal. These are normally sent over well-defined networks with considerable infrastructure that keeps error rates very low. In contrast, radio communications are subject to a wide variety of noises and other signal problems that leads to losses. To forward telex messages successfully over radio links, some form of error correction should be applied. ARQ-M was developed to automatically deal with errors. The automatic repeat request system was invented by Hendrik van Duuren of the Netherlands in the 1940s and so it became known as the Van Duuren automatic error correction system. The seven unit code used was called the Van Duuren code. ARQ was first used commercially in 1947 with a link from Amsterdam to New York with the master station in Amsterdam. In May 1950 the TEX (Overseas teleprinter exchange) service between New York and Amsterdam started. TEX was an early name for TELEX which is a system to allow automatic routing of private messages from a sender to a receiver on the TELEX network. Prior to the introduction or ARQ-M there were so many errors in the messages received that staff from the telecommunications companies had to manually check messages and conform correct receipt. Once ARQ-M was introduced, messages could be automatically and reliably sent over long distances via shortwave radio, and so was introduced into automatic systems. By 1956 ARQ radio circuits were running from New York to Amsterdam, Berne, Brussels, Frankfurt, London, Paramaribo, Paris, Rome, and Wien, with plans for Copenhagen, Lisbon, Madrid, and Oslo. Amsterdam had radio links to Berne, Curaçao, Jakarta, Paramaribo and Rome. Brussels linked to Leopoldville. Frankfurt was connected to Madrid and Rome with plans for Buenos Aires. A link from Madrid to Canary Islands was