RETURN

Trunk 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.