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TUCoPS :: Phreaking Technical System Info :: groundst.htm

Basics of Telephony Ground Start Signaling



Ground Start Signaling


Ground Start Signaling

The following diagrams depict Ground Start signaling states:


     IDLE STATE     - Telephone or PBX On-Hook.  PBX/Telephone monitors for

                      ground on Tip lead.  BAT from CO/FXS appears on RING

                      lead.

PBX SEIZURE

CENTRAL OFFICE SIEZURE

GROUND START FAR-END DISCONNECT


     Both Loop Start & Ground Start signalling will return the line to the

     "idle state" upon local release.  But only Ground Start provides FAR-END

     DISCONNECT supervision.


     Advantages of Ground Start:

     ---------------------------



     Minimizes the possibility of "Glare".



     Provides FAR-END Disconnect Supervision (e.g. the remote user can

     disconnect and the local PBX can be made aware of this and also

     disconnect).





     Disadvantages of Ground Start:

     ------------------------------



     TIP/RING leads cannot be reversed.



     C.O./FXS and PBX/Telephone grounds must be at the same potential (Earth

     ground).





     There is limited support for the Ground Start interface in most PBXs.

     If it is available, Ground Start is usually only incorporated on Trunk

     Interface Cards (e.g. no Line/Station Cards).  Also, it is likely that

     only FX Trunk applications are supported; that is to say, that the PBX

     acts like a station.




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