Hi all,
the highest level of PoE interoperability is obtained if PSE’s supporting 4-pair power switch both conductors of their Secondary Alternative.
As stated in 145.4.1.1:
That’s the only way Type3 and Type4 PSE’s are guaranteed not to cause any issue with Type1 and Type2 PD’s.
Existing (single-signature) Type1 and Type2 PD’s were never designed to support 3-pair power, only real 2-pair.
A Type3 and Type4 PSE can in general not see the difference between a single-signature Type3 PD requesting Class 1 to 4 and a Type1 or Type2 PD
based on the detection and classification process. Therefor the classification, power_up and power_on of these PD’s should be 2-pair then.
As Type3 and Type4 PSE would then already be able to do classification (and power_up) over 2-pair, they could do so:
-
during classification and power_up for single-signature PD’s requesting Class 5 to 6
-
during classification for single-signature PD’s requesting Class 7 to 8
When a Class 5 to 8 PD is powered over 4-pair there can be no backfeed.
Then basically there is no reason anymore to extend the backfeed requirement to 3-pair.
As such, to promote the highest level of PoE interoperability PSE’s supporting 4-pair power must be able to switch both conductors of their Secondary Alternative.
Best Regards,
Joris Lemahieu
Application Engineer
ON
Semiconductor
+32 55 33 29 49
From: Tremblay, David [mailto:david.tremblay@xxxxxxx]
Sent: Tuesday, April 24, 2018 3:19 AM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Backfeed issue - Analysis of the issue and proposals for a solution
Hi All,
Yair’s presentation does a good job highlighting the potential interoperability risks for new Clause 145 Type 3-4 systems if we limit the
PD backfeed requirements to only 2-pairs.
Although Type 1-2 PDs are fully compliant to the existing Clause 33 backfeed over 2-pair specs, they share a similar interoperability risk
when connected to Type 3 PSEs in a 3-pair configuration and no risk when connected to Type 3 PSE’s power demoting to class 4 in a 2-pair configuration.
However, I would not recommend we continue to propagate the risk of potentially reducing the level of PoE interoperability by limiting the
Clause 145 PD backfeed specifications to 2-pairs and excluding 3-pairs.
As such, I support the inclusion of both 3-pair and 2-pair PD backfeed specifications for Type 3-4 PDs in Clause 145 to promote the highest
level of PoE interoperability.
Regards,
David Tremblay
From: Yair Darshan [mailto:YDarshan@xxxxxxxxxxxxx]
Sent: Monday, April 23, 2018 4:08 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: [802.3_4PPOE] Backfeed issue - Analysis of the issue and proposals for a solution
Hi all,
Please find updated presentation regarding the issue, analysis results of some use cases and proposal for solution.
Regards
Yair
Darshan Yair
Chief R&D Engineer
Analog Mixed Signal Group
Microsemi Corporation
1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel: +972-9-775-5100, EXT 210.
Cell: +972-54-4893019
Fax: +972-9-775-5111
E-mail: <mailto:ydarshan@xxxxxxxxxxxxx>.
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