IP Phone twisted pair usage versus PC 10/100
August 2, 2013 8:39 AM Subscribe
Rookie question perhaps...
What more wires in a CAT5 cable other than TX+ TX- RX+ RX- does a standard IP phone use?
I ask because I had one cable run where the PC had 100% connectivity, but when I plugged in an IP phone to the same run, it would not receive an IP (PC was DHCP as well but it shouldn't matter) and resolve to the network. I finally re-punched the wall plate and patch panel and it worked like a charm. I have been combing the web for an answer on this, and the best I found that the phone may require additional wires in the cable if it is PoE, which this particular run is not Powered.
Head scratcher for me...maybe someone out there has an answer!
Thank you :)
They don't. Unless it's some off brand doing something weird, they use 1, 2, 3 and 6 same as your PC. Some will supply power on the other 4 wires, but if it's not a powered run that's irrelevant.
posted by IanMorr at 9:00 AM on August 2, 2013
posted by IanMorr at 9:00 AM on August 2, 2013
Pogo_Fuzzybutt has it. Some devices tolerate a high signal-to-noise ratio better than others. Your PC's NIC did OK with it, but the phone didn't. By repunching, you brought the S/N into a range where the phone could work.
posted by deadmessenger at 9:05 AM on August 2, 2013
posted by deadmessenger at 9:05 AM on August 2, 2013
If you have a spare cable you don't mind sacrificing (or if you're crimping your own, which it kind of sounds like you might be), you can test this pretty easily by cutting away a little insulation and snipping the other four wires.
One possibility that wasn't mentioned is that the pins were switched, crossover-cable style, and the PC knows how to auto-detect that but the phone does not. Would you have noticed that when repatching it?
posted by aubilenon at 11:09 AM on August 2, 2013 [1 favorite]
One possibility that wasn't mentioned is that the pins were switched, crossover-cable style, and the PC knows how to auto-detect that but the phone does not. Would you have noticed that when repatching it?
posted by aubilenon at 11:09 AM on August 2, 2013 [1 favorite]
Most of the phones I've seen have two ports, one to the wall, one to a PC. If your phone is similar, I assume you plugged it in to the right port, but, just in case, I thought I'd raise the issue.
posted by Good Brain at 1:04 PM on August 2, 2013
posted by Good Brain at 1:04 PM on August 2, 2013
This thread is closed to new comments.
What I bet happened was that the wire had a high SNR, and the PC network card was able to manage anyway but the phone couldn't do it. When you repunched it, you fixed the problem.
posted by Pogo_Fuzzybutt at 8:59 AM on August 2, 2013 [2 favorites]