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Loop Start Signaling

The following diagrams depict Loop Start signaling states:

     Advantages of Loop Start:
     -------------------------

     No need for accurate ground references between the Central Office/FXS and
     the PBX/Telephone.

     Generally, TIP/RING wires may be reversed at the PBX/Telephone with no
     adverse impact on operations - (some older DTMF keypads may have problems
     with a T/R reversal, causing no output of tones).


     Disadvantages of Loop Start:
     ----------------------------

     There is no FAR-END Disconnect Supervision.  When the remote
     handset/line hangs-up, there is no provision for the local CO/FXS to
     notify the PBX of the disconnection (Not a problem with a telephone).

     There is poor "glare" resolution.  "Glare" occurs when both the local end
     (PBX/Telephone) and the remote end (CO/FXS) attempt to access the circuit
     at the same time. Unfortunately, with Loop Start, the PBX/Telephone is
     not informed of an inbound seizure until ringing is detected; The ring
     "cadence" is normally 2-seconds ON, 4-seconds OFF (U.S.).

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