3Com 3C10402B Administrator's Manual page 191

Figure 7 shows the pinout for the NBX T1 or E1 Digital Line Card.
Figure 7 T1 or E1 Connector Pinouts
T - TX Tip to PSTN
R - TX Ring to PSTN
T1 - RX Tip from PSTN
R1 - RX Ring from PSTN
Figure 8 shows the pinout for the NBX BRI Digital Line Card.
Figure 8 BRI Connector Pinouts
R - TX Ring to PSTN
R1 - RX Ring from PSTN
T1 - RX Tip from PSTN
T - TX Tip to PSTN
To determine the pinout for the PBX T1 or E1 connector, see the PBX
documentation.
Obtaining a Dial Tone from a PBX System
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