Outside line

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The term outside line comes from telecommunications and describes the process of seizing an outside line.

When establishing a telephone connection via public telephone networks, u. a. a connection is established between the calling set and the central office . This connection goes through the trunk . Typically, the capacity of an exchange is lower than the number of all connected subscribers, so that when the outside line is obtained, the calling subscriber is switched to a free input. If all inputs are occupied, i.e. if the exchange is busy, the outside line will fail.

As a rule, the outside line is obtained automatically when you lift the telephone receiver. The subscriber hears the dial tone and can start dialing. With telephone systems that differentiate between internal and external calls, it may be necessary to pre-dial an exchange code (usually zero) to seize an exchange line. With most telephone systems, the behavior for external calls can be set. If the so-called spontaneous or automatic outside line is activated, the outside line code is automatically pre-dialed when the handset is lifted.

literature

  • Hubert Zitt: ISDN and DSL. Markt + Technik Verlag, Munich 2004, ISBN 3-8272-6630-0 .
  • Werner Bärwald: Expert practice lexicon communication technologies. Networks - Services - Applications, Expert Verlag, Renningen 2009, ISBN 978-3-8169-2843-0 .
  • Volker Jung, Hans-Jürgen Warnecke (Hrsg.): Handbook for telecommunications. 2nd edition, Springer Verlag, Berlin 2002, ISBN 978-3-642-62736-1 .