Zach – this is a perfectly appropriate channel for discussion. I would remind you that IEEE 802.3 is in the individual process, and I take your statements as those based on your individual experience (informed by experience you’ve had
within your employer). A path to success would be to reference generally available material (for example, specifications or standards that the equipment you are referencing is required to conform to).
I hope that helps and appreciate your input.
George A. Zimmerman, Ph.D.
2nd Vice Chair, IEEE 802 LAN/MAN Standards Committee
Chair, IEEE P802.3dg 100BASE-T1L 100 Mbps Long Reach single Pair Ethernet Task Force
Technical editor, IEEE P802.3da 10 Mb/s Multidrop Segments Enhancements Task Force
Technical Committee Chair, Ethernet Alliance
Principal, NFPA 70 (NEC ®) CodeMaking Panel 3, Ethernet Alliance
President, CME Consulting, Inc.
1-310-920-3860
From: Zach Pan <00003dccdc202a28-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, January 8, 2025 8:36 AM
To: STDS-802-3-SPMD@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_SPMD] D2.0 comments 297 and 269
Newbie here. Not sure if I am supposed to reply to this email or use a different channel for my comments. Please let me know.
This is a topic that Schneider are closely followed. In our industrial drive or other equipment, 24V is a commonly used auxiliary power supply voltage, with a typical tolerance band of -10%
to +20%, which translates to 21.6Vmin and 28.8V max. So, we appreciate the comment that calls out that change. Otherwise, it will break the voltage compatibility and require us to add some unnecessary circuit to satisfy a 26V VMPSE(min).
As for the concerns of max power for MPD. It is limited by VMPD(min) and IMPSE(min), which is 16V and 1A in the draft D2.0. 16 W is the limit of type 0 configuration anyway, and the user are
supposed to use type 1 for higher power anyway. So I don’t see the change of VMPSE(min) have any negative impact on that.
Of course. The large gap between VMPSE(min) and VMPD(min) would allows longer wire and higher resistance drop on the wire. The proposed change would reduce the voltage drop allowed on the wire
from 10V to 5.6 V, which means the max wire resistance allowed changes from 10Ohm to 5.6 Ohm. I don’t see that as a problem, but we could specify a minimum wire size for given wire length to guarantee that is meet.
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Best regards,
Zach Pan
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General
From: Chad Jones (cmjones) <00000b60b3f54e8d-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, January 8, 2025 9:26 AM
To: STDS-802-3-SPMD@xxxxxxxxxxxxxxxxx
Subject: [802.3_SPMD] D2.0 comments 297 and 269
[External email: Use caution with links and attachments]
These two comments assert that the VMPSEmin voltage should not be 26 V but instead should be 21.6 V. I dug through the history and this text was added in Nov 2023, via this presentation:
https://www.ieee802.org/3/da/public/1123/clause169_clean.pdf (though there is a presentation there with markups and I don’t recall if this is something we marked up during the meeting
and imported the edited version:
https://www.ieee802.org/3/da/public/1123/clause169_edits.pdf). Regardless of which file was used, Table 169-1 is the same in both locations:
So VMPSEmin has been 26 V from the start. I’m opposed to lowering the minimum voltage because that will then also lower the guaranteed MPSE power. The average power available to an MPD is already low (26 V * 1 A / 16 nodes = 1.625 W), the
change to 21.6 would reduce by about a quarter watt per MPD, or about 17%. I’ve stated many times, the one complaint we will get after publication is “how do I get more power, I need X more watts for my application.” I’m very focused on optimizing power delivered
to prevent a follow-on standard only to raise the power.
I’d expect a presentation justifying 21.6 V and it will take convincing 75% of the TF to make this change. I will not be one of those 75%.
Regards,
Chad Jones
Principal Engineer, Cisco Systems
Executive Secretary, IEEE 802.3 Working Group
Chair, IEEE P802.3da Task Force
Principal, NFPA 70 CMP3
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