<Actually, you can link 2 together - Tx terminals on one to Rx terminals <on the other and vice versa. Works with twin twisted pair cable up to a <few hundred metres (? Maybe a little more). If it's a short haul modem the limit is some 4000ft at something like 9600 or maybe even as fast as 38.4k. Used to used them in the DEC Mill for links off the eithernet using synchronous DUV-11s. Allison