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Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx



It is data-only feature. The transceiver will cross the data path internally but the physical connection of the power delivery path remain the same.




From: Hauer, Goran (Goran) [mailto:ghauer@xxxxxxxxx]
Sent: Thursday, February 06, 2014 5:44 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] SV: [802.3_4PPOE] Are diode bridges really needed (2).pptx


Hi Christian, all,


I would assume that it is a data feature only.


However, it would be really nice to remove those rectifying bridges from the PD, to both increase efficiency and reduce cost and complexity in the PD.


I have taken a look at what could be done at the PSE side.

If you could consider that a 4-pair powered device (PD) would accept power a bit differently from the old PoE standard, by instead powering the pairs 3,6 and 4,5 with the negative voltage and the pairs  1,2 and 7,8 with the positive voltage, the polarity at the PD side wouldn't change regardless of straight cable, "Val's Crossover Cord" or "Goran's Crossover cord".

The PSE would then need to be able to swap polarity between two of the pairs (for instance between pairs 4,5 and 7,8) to maintain compatibility with the old PoE standards.


When typing this down, I came to think about that it could maybe be solved even more elegantly by supplying the pair 4,5 with the negative voltage and the pairs  1,2 and 7,8 with the positive voltage regardless, and after identification of the PD type, the PSE would either power the pair 3,6 with positive voltage for an old (2-wire) PoE PD or with negative voltage for a 4-wire PoE PD. The 4-wire PD would then need to be able to connect the pairs 3,6 and 4,5 together in the powered state. It would also need to be able to rectify the voltage on the pairs 3,6 and 4,5 during detection and negotiation (classification). This reduces the total number of needed transistors at the PSE and PD but adds a rectifier (that only need to support detection and negotiation currents) and a switch (transistor) to the PD. This PSE solution would also only support 2-wire powered PoE PD that accepts power on the data pairs.


There should be other possible solutions to be able to get rid of those rectifying bridges, I would be happy to see some more brainstorming about this.


Best regards,



Från: Christian BEIA [mailto:christian.beia@xxxxxx]
Skickat: den 6 februari 2014 09:53
Till: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Ämne: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx


Thanks Peter, all,


Let’s consider a PSE switch where those transceivers with Auto-MDI feature are present.  

Would it automatically  adapt the port voltage polarity as well? Or is it a data-only feature?


best regards,





From: Peter Johnson [mailto:peter_johnson@xxxxxxxxx]
Sent: Wednesday, February 05, 2014 7:14 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx




It might be telling that there are 10/100/1000 PHY transceivers that automatically adapt to crossover (Auto-MDI) with BOTH the "data" pairs (1,2/3,6) and the "spare" pairs (4,5/7,8) independently.



Pete Johnson




-------- Original Message --------
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx
From: Christian BEIA <christian.beia@xxxxxx>
Date: Wed, February 05, 2014 10:51 am
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx

Hi Val,

a “4-pair crossover” is a cable which inverts voltage polarity on both 1,2 / 3,6 pairs and  4,5 / 7,8 pairs.

In other words 1,2 pair at one end is connected to 3,4 at the other end, and 4,5 is connected to 7,8.


I don’t know if such a cable complies with any standard, but it seems that exists on the market.



did I understand correctly?


Bet regards




From: Valerie Maguire [mailto:Valerie_Maguire@xxxxxxxxxx]
Sent: Wednesday, February 05, 2014 4:21 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx


Hi Christian:

What is a “4-pair crossover” cable?  Is a modular cord that is wired T568A on one end and T568B on the other?  If so and this cord is used as designed, it would ensure that the same pair combination is "split" (e.g. terminated to pins 4,5 and 3,6) on both ends of the channel.

All the best - Val

From:        Christian BEIA <christian.beia@xxxxxx>
To:        STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx,
Date:        02/05/2014 01:55 AM
Subject:        Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx

Thank you Goran,
I was not aware about this case.
Is there anyone who can tell if those “4-pair crossover” cables are standardized or not?
Thank you
Best regards
From: Hauer, Goran (Goran) [mailto:ghauer@xxxxxxxxx]
Friday, January 31, 2014 4:41 PM
Re: [802.3_4PPOE] Are diode bridges really needed (2).pptx

Hi guys
I haven't participated in any meetings live, but I have been subscribing to this list for quite some time. Great work you guys!
When I saw this presentation however I must say that I have seen (and used) crossover cables intended for 1000BASE-T that crosses all four pairs, whether they are standardized or not that I can't tell, but they are out there.
Best regards,
Från: Chad Jones (cmjones) [mailto:cmjones@xxxxxxxxx]
den 31 januari 2014 16:14
[802.3_4PPOE] FW: Are diode bridges really needed (2).pptx
Christian, the reflector should be able to handle attachments up to 2MB in size.
All, I am forwarding this on behalf of Christian. He is looking for some help to decide if we can pursue removal of auto-polarity in the PD.
Christian, I am going to forward this to Pat Thaler (I’m not sure that she’s subscribed to our reflector). I will copy you. It was her comment in AF that eventually led to us mandating autoMDIX support.
Chad Jones
MGR, HW ENG, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force
From: Christian BEIA <christian.beia@xxxxxx>
Friday, January 31, 2014 at 6:02 AM
Yair Darshan <
YDarshan@xxxxxxxxxxxxx>, Fred Schindler <fred@xxxxxxxxxxxxxx>, Dave Dwelley <ddwelley@xxxxxxxxxx>, "Picard, Jean" <jean_picard@xxxxxx>, Chad Jones <cmjones@xxxxxxxxx>
"Yseboodt, Lennart (
lennart.yseboodt@xxxxxxxxxxx)" <lennart.yseboodt@xxxxxxxxxxx>, "Abramson, David" <david.abramson@xxxxxx>, "Kousalya Balasubramanian (kousalya.balasubramanian@xxxxxxxxx)" <kousalya.balasubramanian@xxxxxxxxx>
Are diode bridges really needed (2).pptx

Hi Guys,
I’m trying to find out if having a defined voltage polarity at the PD PI is an achievable goal.
Please look at the short presentation in attachment. It summarizes the spec we have today.
After this brief research, my understanding is the following:
About Alt-A: reverse polarity at the PD happens only if a MDI-X cable is used and there is no auto-detect mode
About Alt-B: reverse polarity at the PD should never happen.
Are those assumption correct?
If they are correct, I would like to understand if auto-detect mode is a common feature or it is something “advanced”.
I can imagine that a Midspan probably won’t have an auto-detect feature. But what is the reason for using MDI-X cables between the midspan and the PD?
Thank you for any comment
Best regards
I’m not using the reflector since I’m not sure I can attach presentations there.
If it is ok I will forward this email to the reflector.

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