atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking Power Over Ethernet Question

I haven't done any extensive troubleshooting on this yet (tomorrow, probably), but here goes:

I have a wireless AP (Cisco) running off of a Cisco POE switch. I'm at the distance limit (324' including patch cables). We can see activity on the port on the switch, but can't read a MAC address. When I short-cable the AP to the switch all is good. The cable tests OK. There appears to be no problem with the cable installation, nor does there appear to be any influence from other devices/equipment/power sources along the way. Tomorrow I plan to swap a known-good unit with the questionable one to see if it works, as well as putting the questionable unit on a known-good cable of similar length. I also want to check the voltage at the device end.

I have a couple of questions, since I don't know enough about POE.
1. Is there any significant voltage drop over distance with POE?
2. Any out-of-the-ordinary environmental considerations?
3. Any other troubleshooting steps?

Thanks,
Bill

I believe the distance limitation is shorter for POE.. Is there any way that you can power the AP from where it is at? Would probably be the best way.

PoE is designed for 100m, just like ethernet. 324' is right at the edge, but it should work with all standard compliant equipment.

The switch should be able to log POE events, with the right configuration. I'd also verify PoE is enabled on the switch port (I'm guessing you already tested that) and that the switch is not exceeding it's power budget (many switches can't support a PoE device on every port).

That said, my guess is that you don't have all 4 pairs going all the way through, perhaps either splitting out a pair or using a patch cable somewhere with only 2 pair in it. Have you verified that all 4 pairs go straight through the entire system (including patch cables)? Not all PoE needs 4 pairs, but some do.

Mid-span POE is pins 4,5,7,8

af poe use standard ether pins 1,2,3,6

I think that is right.

known good device is always good to have.

Connect the device right to the sw to be sure it works properly.

then move out observing what is and is not happenign to decide the next move.

Best of luck to you.