A modem sharing device (MSD), also commonly known as a line sharing device (LSD), modem sharer, or line sharer, allows multiple devices to share a serial connection. Only multipoint serial protocols such as Bisync are supported. Both synchronous and asynchronous datastreams can be used. A common example would be a Tandem as host connected to multiple automatic teller machines often with a modem or Cisco router in-between.
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Modem sharing device Wikipedia(Text) CC BY-SA