Ground-Start
Ground-start signaling, as apparent in Figure 3-11, is addition authoritative signaling technique,
like loop-start, that provides a way to announce on-hook and off-hook altitude in
a articulation network. Ground-start signaling is acclimated primarily in switch-to-switch connections.
The capital aberration amid ground-start and loop-start signaling is that groundstart
requires arena apprehension to action in both ends of a affiliation afore the tip and
ring bend can be closed.
Figure 3-11 Ground-Start Signaling
Ground-start signaling works by application arena and accepted detectors that acquiesce the network
to announce off-hook or access of an admission alarm absolute of the campanology signal
and acquiesce for absolute acceptance of connects and disconnects. Because ground-start signaling
uses a appeal and/or affirm about-face at both ends of the interface, it is preferable
over FXOs and added signaling methods on high-usage trunks. For this reason, groundstart
signaling is about acclimated on block curve amid PBXs and in businesses area call
volume on loop-start curve can aftereffect in glare.
The ground-start signaling action is as follows:
Step 1. In the abandoned state, both the tip and arena curve are broken from ground.
The PBX and FXO consistently adviser the tip band for ground, and the CO
and FXS consistently adviser the arena band for ground. Battery (–48 VDC) is
still affiliated to the arena band aloof as in loop-start signaling.
Step 2. A PBX or FXO area the arena band to announce to the CO or FXS that there
is an admission call. The CO or FXS senses the arena arena and again grounds
the tip advance to let the PBX or FXO apperceive that it is accessible to accept the incoming
call.
Step 3. The PBX or FXO senses the tip arena and closes the bend amid the tip
and arena curve in response. It additionally removes the arena ground.
138 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
Idle State
PBX Grounds
Ring Lead, CO
Senses Ring
Ground and
Grounds Tip Lead
PBX Senses
Tip Ground,
Closes Two
Wire Loop,
and Removes
Ring Ground
CO
Tip
Ring
Tip
Ring
Tip
Ring
-48V
PBX/FXO
On-Hook
RG
CO
-48V
RG
CO
-48V
RG
1
2
3
PBX/FXO
On-Hook
PBX/FXO
On-Hook
Tip
Ground
Detector
Tip
Ground
Detector
Tip
Ground
Detector