A method of distributing DMX512 using category 5, 5e, 6 computer networking cable. The signal IS NOT converted to a network signal, and thus standard router s, hub s, switch es, etc. CANNOT be used.
It's been standard procedure for a short time to use CAT5, rather than DMX, cable for permanently wiring. CAT5 is slightly less-expensive, more familiar to contractors, and allows a degree of future-proofing--the connectors/wall plates can be changed at a later date to allow computer networking without the need to re-pull the wire.
The use of CAT5 cable for portable applications is hotly debated, but most agree that for now, it's best continue using DMX (EIA-485) compliant cable with 5pin XLR connectors.
A standard pin-out has been established. From http://www.etcconnect.com/Support/Articles/DMX-Over-Cat5.aspx :
Pin (Wire) # Wire Color DMX512 Function 1 white / orange data 1+ 2 orange data 1- 3 white / green data 2+ (optional) 6 green data 2- (optional) 4 blue Not assigned 5 white / blue Not assigned 7 white / brown (Common Reference) for Data 1 (0v) 8 brown (Common Reference) for Data 2 (0v)
Note also the caveats involved, as detailed on the site.
One of many threads on the topic: http://www.controlbooth.com/forums/lighting-electrics/30465-cat5-over-ceiling.html .
Do not confuse with DMX-over-Ethernet.