Multiplayer Options : Null-modem cable
A null-modem cable is a serial cable with pins 2 and 3 reversed at one end. Connecting this cable between two computers allows them to communicate easily. Games that support null-modem cables can obviously only network between two computers.
Sometimes called "serial cable" networking, even though a "normal" serial cable is not used.
Null-modem cable is part of the Multiplayer Options category.