private-line car

Private line

In wired telephony, a private line or tie line is a service that involves dedicated circuits, private switching arrangements, and/or predefined transmission paths, whether virtual or physical, which provide communications between specific locations.

Note: Among subscribers to the public switched telephone network(s), the term "private line" is often used to mean a one-party switched telephone line, as opposed to a party line.

Source: Federal Standard 1037C


In radio or wireless telephony, Private Line is a term trademarked by Motorola to describe their implementation of a Continuous Tone Coded Squelch System (CTCSS), a method of using low frequency subaudible tones to share a single radio channel among multiple users. Each user group would use a different low frequency tone. Motorola's trade name (especially the abbreviation PL) has become a genericized trademark for the method. General Electric used the term 'Channel Guard' to describe the same system and Other manufacturers used other terms. A later digital version of Private Line was called Digital Private Line, or DPL.

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