Specifications

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Simplified TELCO Configuration Schematics
PABX E&M Type I Tie-Trunk (2-wire audio)
Simplified TELCO Configuration Schematics
The following diagrams are simplified schematics of the four standard telco interfaces. In
conjunction with the previous text descriptions, they can help you and your telephone
service provider understand the telephone interface.
The Answer relay is shown in idle condition in these schematics (no call in progress).
Signal Name Purpose
RING Paired with TIP signal. Carries balanced audio
TIP Paired with RING signal. Carries balanced audio
E Paired with M signal
To telco system to answer and terminate telephone call
M Paired with E signal
From telco system to originate and terminate telephone call
Chassis GND Protective earth ground
Carries return current for E and M signals