We are replacing an analog PBX with a NV7100. The analog system has an OPX line connected to another facility down the street that also has an analog PBX. I'm thinking that the OPX is simply connected to an FXO port and treated like a trunk. Is there more to it than that?
You are correct. Assuming the far end PBX is supplying Battery (FXS), then that would come into the 7100 FXO port.
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