Look into http://en.wikipedia.org/wiki/EIA-485

EIA-485 (also known as TIA/EIA-485 or RS-485) enables the configuration of inexpensive local networks and multidrop communications links. It offers data transmission speeds of 35 Mbit/s up to 10 m and 100 kbit/s at 1200 m. Since it uses a differential balanced line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 meters).