I'm pretty sure this query is going to make me sound like an imbecile, but anyway.

We have some basic IP cameras (D-link DCS 930L). We didn't need anything fancy, and these play really nicely with our NAS, which is set up with D-Link's "My Surveillance" feature. Assuming everything works, we may invest in some better cameras later, but that's for another day.

I'd like to move a couple of the cameras to a place where there isn't a ready power socket, so have been reading about PoE but google sends me into a world of terminology that includes "active", "passive" and 802 standards, and I need a bit more of a 101.

So far as I can tell, the cameras don't natively support PoE (though I did get fooled very briefly after seeing PPPoE on the box - like I say, imbecile). So what I think I need is a PoE injector and splitter set - you move the power brick to a power socket near your switch, the injector combines the data and power feeds into a single cable, then the splitter splits out data and power feeds at the other end, and you connect the data feed to the ethernet port and the power feed to the power port using the appropriate connectors. The power travels over the spare pairs in the ethernet cable (the cameras only support 100Mb connections.

The cable runs aren't huge, probably 20 meters tops.

Is that about right? Or have I missed something critical that will end up frying either the cameras or me? Will any cheap injector/splitter set work, or is there something in particular I should be looking out for?

Separately, I also need to upgrade the switch, and see some that have inbuilt PoE. I am guessing that this will only support devices at the other end that natively support PoE? Or can you use these with a splitter too? Do PoE devices actually receive power through the ethernet socket?

Finally, can anyone enlighten me as to the difference between active and passive PoE? How do I tell whether a device that has PoE needs an active or passive supply?