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

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.