Actually, a cross over network cable is not a "null" per se, you are referring to a serial cable, the cross over has the TX+/- and RX+/- pairs crossed. Also, a switch will allow you to use cross overs if it supports Auto-MDIX (Automatic Medium Dependant Interface Crossover), most do these days, or most decent ones do I should say rather.
A single cable (cross over) between 2 stand alone PC's will create a point to point connection, a cable into a switch will create a multi-point connection.
I tend to think of 2 machines connected via cable, a direct connection, or point to point, a machine connected to a switch, which goes on to a gateway and / or many other machines is a "network".