"I think you can use data pump chips instead of RS485 for long distance."

I think the term "Data Pump" is usually used to indicate just the modulation/demodulation part of a MODEM - ie, without all the Hayes 'AT' commands, call-control, etc, etc
As such, it is not the "Data Pump" itself which gives the long distance capability, but its associated line interface

A PSTN Subscriber Line Interface provides a point-to-point link, and would not be suitable for the networked requirement indicated by the original post.