Networks·41,460 discussions

4 pin POE over center pins?

Tags: Networking

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 ?

Topic

We’ll have to look closer at the phone.

In reply to 4 pin POE over center pins?

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

Awesome

In reply to We’ll have to look closer at the phone.

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?

Sorry.

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.

Sorry.

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.

Awesome

In reply to We’ll have to look closer at the phone.

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?

We’ll have to look closer at the phone.

In reply to 4 pin POE over center pins?

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

PoE Switches In Detail

In reply to 4 pin POE over center pins?

Not in every case. It depends upon the technology they are using to provide PoE. And yes, in most cases PoE phones need PoE on the centre pins, a bit different from PoE cameras.

There are also endpoints that power on the spare pairs, 3,4, and 7,8. So again, it comes down to the manufacturer and how the endpoints are manufactured to negotiate PoE. You can have a look at NVT Phybridge’s products here, they do long reach PoE on both Coax and UTP cable. They have adapters that can provide data and PoE on all 4 pairs or Data on the Spare pairs. This will come in handy with endpoints that expect PoE on certain pairs of cabling.

[Author]

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