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Analog Voice ModulesPassport 4400 Hardware Installation Manual
6-2
Signaling Formats
Use the information and figures below to ensure you are using the correct
interfaces in your Analog Voice Modules.
FXS
• Provides ringing voltage and battery to the attached telephone
equipment.
• Selected when the voice channel is connected directly to a telephone
instrument, to the trunk side of a key telephone system, or to the central
office trunk of a Private Branch Exchange (PBX).
• Must never be connected to a telephone interface that also provides
ringing voltage, such as Central Office equipment, a PBX station, or off-
premise circuit.
Figure 6-2. Interface Requirements for FXS
FXO
• Normally attaches to the station side of a PBX or Central Office loop
start equipment.
• Accepts ringing voltage from the attached Central Office line of PBX but
does not provide ringing voltage or battery.
Figure 6-3. Interface Requirements for FXO
Voice Channel
FXS
Key
Telephone
System
PBX
Trunk Side
Station Side
When the Telephone Interface is:
Use
FXO
C
PBX
Voice Channel
Trunk Side
Analog
Station Side
When the Telephone Interface is:
Use