From the User Guide for the rainbow brain.
Rainbow Light Connections
The 5 jacks located between the power jacks are there to power your Rainbow lighting devices. A connection can be made between the lights and the board with a standard Cat-5 cable. It is important to understand that each jack has a limit to the amount of lights that it can power. *At no time should more than 3 Rainbow Wall Runners or 2 Rainbow Flood Lights be connected together on one jack!*
DMX Addressing
The Rainbow Brain uses a standard DIP switch for setting its DMX address. The technique for setting the address is not difficult to understand, but if you have never set a device like this, you will need to read the following section carefully.
it is a 15 channel DMX controller
each port would have 3 channels R, G, and B then the next port would have 3... 5 ports times 3 rgb = 15
if you set the device as channel1, then 1 through 15 would be the channel numbers that it would use.