POE switch or cable length issue

markmarvinq · ‎08-03-2015

Hi All,

I have problem to one of our device(IP Phone) connected to my switch(POE). Cable length is 150 meters and no option for fiber.

Initially it was working fine for few days then the IP phone was off, on the switch interface there is err-disable. Shutting off and on the interface will make it works again.

So we decided to put small Cisco POE(unmanageable) switch near the device assuming it can attenuate the signal and we are suspecting it is a cable issue. But after sometime same thing happens the IP was off.

I really need some advice on how we can fixed this issue.

Thanks in advance.

Mark

Peter Paluch · ‎08-03-2015

Hi Mark,

Two things. Regarding the err-disable situation, it is crucial that you find out why the port got err-disabled. There are several reasons why this could have happened, and we need to pinpoint down the exact reason. When that happens again, please issue the show interfaces status err-disabled command and copy&paste here the output.

Regarding the cable run, 150m of xTP cabling is way over permissible standards. No Ethernet device is built or certified to work with such a cable length. If the cable length is truly the problem, there is no guaranteed way of solving this issue just by configurational changes because the devices are not constructed in their hardware to deal with the kind of signal deterioration that occurs beyond 100m. If they work now, it is because of their positive manufacturing tolerances but it is nothing to rely upon. The length of the cabling must be corrected so that there is no more than 100m of cable between any two active devices. Putting a possibly unmanaged switch in the middle of the 150m run is one option - albeit awkward, it will solve the problem of overlong cabling as long as each cable leg going from that added switch is itself not more than 100m long. Remember: the 100m limit between any two directly connected active Ethernet devices is an absolute.

Best regards,
Peter

ndemers · ‎08-03-2015

Peter has an excellent point. The cable is 50% longer than maximum acceptable standards. You probably have a tone of degradation on your signal.

Now when he says put a switch out there he's right i could be awkward however you have other options. There are cable signal extenders that are pretty tiny if you only need one cable.

I am not promoting this product I am only using it as a reference. This model offers POE as well.

http://veracityglobal.com/products/ethernet-and-poe-devices/outreach-max.aspx

Peter Paluch · ‎08-03-2015

Hi,

Hmm - interesting! I didn't know about those devices. So this type is powered from the PoE itself, right? It could be kind of interesting to find out whether the remaining power available to a powered device - after the incurred losses over 150m of cabling - would be sufficient to drive a Cisco IP phone. Nonetheless, good to know!

Best regards,
Peter

ndemers · ‎08-03-2015

Im curious myself. You might have to adjust the POE power settings to accommodate, if able. The documentation for this one indicates 60 watts output.

According to Cisco (this doc below) since 2011 they use "UPOE" which is up to 60 watts for POE. http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-4500-series-switches/white_paper_c11-670993.html

So if able, he could raise the output in the POE settings on the switch to accommodate the extra pull from the extender.

ranjithkumarpullaikodi100 · ‎01-19-2020

For me also i have same issue. Have u got any solution for this case.