Networks

Question

4 pin POE over center pins?

By Tomlg123 ·
Hello,

I just came back from a client site today after repatching a cable installed by one of the electricians.

After some investigation it looks like pins 1,2 and 7,8 are not terminating correctly to the patch panel which goes to a POE switch.

I am using t568B for reference.

I was surprised to find that when someone plugged a poe phone it worked with only 3,4,5&6 pins terminated.

My understanding of 100base cabling for POE used pins 1&2 for for Transmit and 3&6 for Receive.

If this is the case then the phone surely should’t even switch on let alone dial out.

My question is why/how does it work?

Thanks in advance to anyone who pics this up ?
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All Answers

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We'll have to look closer at the phone.

by rproffitt Moderator In reply to 4 pin POE over center pin ...

But at the least it has power and one data pair so maybe they support Single Pair?

https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Single-pair

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Awesome

by Tomlg123 In reply to We'll have to look closer ...

Thanks for your reply.

I believe its just a bog standard polycom poe phone theyre using.

This is really interesting because I honestly didn’t think single pair was possible.

So I’m guessing its autonegotiating between the phone and the switch to use what ever is wire is available to communicate. Thats quite incredible really.

Is there any industrial standard documentation for this do you know. Like IEEE standard?

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Sorry.

by rproffitt Moderator In reply to Awesome

I tried to get you started with the Wikipedia entry but you want an IEEE standard. I think the following is enough:
https://www.google.com/search?&q=ieee+ethernet+single+pair

A search about some Polycom lead me to https://en.wikipedia.org/wiki/Power_over_Ethernet which again noted single and other pair Ethernet IEEE standards.

-> Remember that I can't answer any direct answer about this phone system as:
1. No exact models listed for both phone and the POE and switches used.
2. Even with item 1, Polycom may not document such.

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