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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. Most private lines connect only two locations though they may be switched at either end or both. Some have multiple drop points.
Among subscribers to the public switched telephone network, the term private line is often used to describe an individual (one-party) telephone line, as opposed to a party line with multiple stations connected.
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 is called Digital Private Line (DPL).
- This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
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