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:''This article refers to a specific series of historic telephones. For multi-line phone systems in general, see private branch exchange or key telephone system.'' A Multi-Line Extension, or MLX telephone, is a no-longer-manufactured series of digital telephone used with several PBX systems sold throughout the 1980s and 1990s by AT&T. This series is notable for the sheer quantity of devices operating in the field, and for its after-market continuing long after the manufacturers stopped making them. Their popularity has also contributed to the existence of a sizeable refurbishment market. These phones are typically used with the AT&T Merlin PBX system, originally known as the American Bell Merlin, also sold under the Lucent/Avaya names. The systems they work with include the ''Merlin Legend'' and ''Merlin Magix''. A similar style of phones, with the model MLS, was designed to work on the AT&T ''Partner'' systems, but could also be used on the Merlins with optional expansion modules. Although there are several versions of MLX telephones, all of them resemble typical business telephones, with anywhere from 30 to 80 buttons on their keypads. Their most common usage is in offices. ==Communication protocol== MLX telephones use an unpublished digital communications protocol based on ISDN S interface. They connect to their host system using an 8-position 8-conductor connector, however only the middle 4 positions are actually used. The processing for an MLX telephone is done principally by its host - the keypad and display is essentially the equivalent of a dumb terminal contained inside the set. There are provisions for two independent two-way voice channels and the data channel (similar to ISDN BRI) going to a single telephone set. Because each channel is two-way, the two voice channels are rarely used simultaneously, except for example, when a voice "paging" announcement comes over the speakerphone while somebody is using the line, or if an additional "multi-function-module" accessory is attached to the phone that permits the second voice channel to be used as a normal analog telephone line, such as for a modem or fax machine. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Multi-Line Extension telephone」の詳細全文を読む スポンサード リンク
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