Re: [802.3_ISAAC] Invitation to the 802.3dm comparison study

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Hello Jay,

thank you for your response and explanation. From my understanding of both your’s and TJ’s email I get that there is some overlap and reuse between GMSL and ACT. I see that there has indeed been a misunderstanding from my side concerning the frequency overlap. Your plot shows a full frequency overlap of both US and DS directions. Furthermore, I understand that there can be overlap in product specific features (power supply, power delivery and lane configuration), and some reuse in the PMA (e.g. not the same line rate but similar), while the PCS is different, including scrambling, line coding and FEC.

So, I hope that we can agree that, while there is some overlap, but nothing close to backwards compatibility between ACT and GMSL (as the name GMSLE suggests). I find that the overlap is in a range that many other two different technologies might have. Could you share a detailed estimate on how much additional chip area a GMSL 2/3 PHY would need if it tried to accommodate ACT in a dual mode version and vice versa? In % and mm²? As TJ mentioned the coaxial media considerations, would you mind sharing with the group the link lengths that GMSL 2 and 3 currently support for STP and Coax at 3Gbps, 6Gbps and 12Gbps line rates?

Your email, and the issue of naming something GMSLE in general, raises an additional concern to the one that the naming is misleading potential customers into believing that GMSLE is backwards compatible to GMSL. If your intention is as forward looking as you state, why tie the naming to something that today (and for some time in the future) is a single vendor technology, whose trademark and IP is owned by a single company, which has a significant market share in the Automotive SerDes market on top (according to your own account)? The naming GMSLE is marketing for GMSL, whether rightly so or not. Do you seriously want to claim that you do NOT expect any advantages for your affiliation in the existing SerDes market based on this? I am surprised that the leadership responsible for this group is not going haywire on this. For me this whole naming endeavor is not only a breach of the IEEE code of Ethics, it is also an antitrust concern, to which I herewith formally object.

And one more item. GMSL is a proprietary technology today. All implementations and real life experiences with it (or its proprietary competitors) are under NDA. So while, of course, all positive comments are not a concern, I wonder how anyone can be ok with considering to adopt something similar to a technology (tied together by naming!) on which anything critical can actually not be shared!

Kind regards,

Kirsten

Von: Cordaro, Jay <Jay.Cordaro@xxxxxxxxxx>
Gesendet: Montag, 2. Juni 2025 02:34
An: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx; Matheus Kirsten, EE-352 <Kirsten.Matheus@xxxxxx>
Betreff: Re: Invitation to the 802.3dm comparison study

Hi Kirsten,

You said, "As far as I can see, there is no overlap or reuse between [the technology known as] GMSL 2/3 and ACT[+GMSLE], not even in the duplexing method."

I'd like to clarify a few points.

First, regarding the duplexing method, you might be thinking of the technology known as GMSL1, which does exhibit limited frequency overlap between high-speed and low-speed directions. In contrast, the technology known as GMSL3/2 does not have the limited overlap between the low speed and high-speed directions that GMSL1 has.

As illustrated in the attached plot (see notes below), the technology known as GMSL2 operating at 3Gbps demonstrates has, in fact, complete overlap between high-speed and low-speed directions. The 9b10b encoding of GMSL2 does provide low frequency shaping of the PSD but there is still complete overlap. So, both GMSL2 and 64B65B encoded technology known as ACT+GMSLE utilize the same duplexing method although they have different scrambling and line coding schemes.

Although it does not preclude other approaches to handle the high speed and low speed overlap in ACT+GMSLE, the same echo subtraction approach utilized in GMSL3/2 may be used. While the 9b10b encoding of GMSL2 allows a high-pass filter to be applied at the high-speed receiver to suppress low frequency echo residue from the low-speed transmitter without introducing baseline wander, there are several techniques which could be employed with ACT+GMSLE including high-pass filtering with a baseline wander compensation circuit.

Secondly, concerning reuse between ACT+GMSLE and GMSL3/2, I have thoroughly reviewed the ACT+GMSLE proposal for IEEE 802.3dm and discussed it with designers affiliated with my company. We have determined that there is significant IP reuse between parts of the PMA for GMSL3/2 and ACT+GMSLE. In addition to the same echo subtractor being applicable to both ACT+GMSLE as well as GMSL3/2, the Baud rate in the high-speed direction is very similar, and the same line drivers and high-speed mixed signal receiver (CTLE+DFE) can be utilized as-is. A CDR can support both rates. While other receiver approaches may be employed, there is sufficient commonality between ACT+GMSLE and GMSL3/2 to enable the use of a single transceiver IP for both with minimal additional complexity. The primary difference in a common high-speed receiver is, in my opinion, the baseline wander compensation circuit which may be required if echo subtraction duplexing for ACT+GMSLE mentioned earlier is used. The ACT+GMSLE 117.1875Mbps DME upstream differs from the 187.5Mbps NRZ low speed in GMSL3/2, however as I demonstrated in my contribution, the ACT+GMSLE low speed receiver can be of very low complexity and exceed the immunity levels presented in Neven and Mehmet's contribution.

The PCS digital logic and the MAC interfaces differ between 802.3dm and incumbent FDD solutions. This is not a surprise as one is Ethernet, and one is not. However, the intent, particularly with the reduced complexity of the combined and simplified ACT+GMSLE, is that many mixed signal blocks of the PMA and PMD can be reused between GMSL3/2 and ACT+GMSLE.

Rather than focusing on backward compatibility, my intention is to help define the standard to support "forward compatibility," enabling the same IP to be used with both an FDD CSI-2 based SerDes today and an ACT+GMSLE Ethernet MAC interface PHY in the future.

Regarding your statement, "If someone wants to implement a dual port ACT/GMSL PHY, it would be two PHYs next to each other." Yes, of course, a dual port PHY would require two PHYs next to each other. However, if instead you were referring to a dual-mode PHY, as I explained above, it is possible to develop IP blocks in the PMA which would support both approaches or even build a monolithic PHY IP PMA and PMD supporting both if someone wanted to.

I and my co-author contributed GMSLE to 802.3dm with the hope of converging the two separate paths of the Task Force towards a common objective. I and my GMSLE co-author have worked with individuals affiliated with ACT to incorporate several ideas from GMSLE into the merged proposal which reduces the implementation complexity. In my opinion, the term 'ACT+GMSLE' is justified.

I welcome comments on the reflector or at Ad-Hocs, IEEE Interims, and Plenaries regarding my contributions. For instance, several individuals have provided constructive technical feedback on my DME presentations, leading to improved analysis, simulation, and meaurement, which I intend to present in a future meeting. I am also prepared to review others' contributions, comparisons, and comments on the reflector and at IEEE meetings.

Cordially,
Joseph L. "Jay" Cordaro
Affiliation: Analog Devices

the attached picture shows in log frequency scale the output PSD of both sides of the link with the technology known as GMSL2 in the forward, high speed, 3GBaud NRZ and reverse, low speed, 187.5Mbps NRZ directions overlaid on the same graph. The PHY was operating in single-ended coax mode. The PHY is transmitting random data and is not in a test mode. I have overlaid the one-sided single-ended PSD of the proposed technology known as ACT+GMSLE in the downstream and upstream directions with the transmit levels, 64B65B encoding ,and Baud rates proposed. Random, scrambled data was generated.

From: Matheus Kirsten, EE-352 <00004506adf647e4-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Friday, May 30, 2025 5:42 AM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx <STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx>
Subject: [802.3_ISAAC] WG: Invitation to the 802.3dm comparison study

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p.s.

You end your email with “so thank you for clarifying that you are open to changing your mind and support ACT/GMSLE if presented with good arguments”.

The dm group would not be in the situation it is, if the individuals supporting ACT and the individuals supporting TDD, did not believe that they each had good arguments (though I like the “if” in your statement, but that is a different matter 😉 ). Part of the openness to change your mind is the willingness to listen. This is what the comparison effort is about: To find metrices that allow a direct comparison on an apple to apple basis, leaving marketing pitches aside. Bringing together a lot of what has already been presented and fill the gaps in a way that helps to understand where the disconnect is. Maybe this allows the group to advance. That is what this is all about, to find constructive means to move the group forward. I would also have liked to see this as an official adhoc, however, that was not my/our decision. It is NOT the goal to make any judgement in the comparison. The opinion on which criteria is seen as how important should stay with every individual looking at the data and the rationales. I agree that to achieve something meaningful requires effort and time. Nevertheless, if you have good arguments that you think they withstand a direct multi-sided comparison, bring them into the discussion. I would like to hear them.

In respect to marketing: I have compared the technical parameters of ACT with those of GMSL, which you find summarized in the table below. As far as I can see, there is no overlap or reuse between GMSL 2/3 and ACT, not even in the duplexing method. If someone wants to implement a dual port ACT/GMSL PHY, it would be two PHYs next to each other. However, you call your proposal ACT/GMSLE (also in your cited comment above). Calling something GMSLE causes the association that it is closely related to GMSL (there is NO question on this), if not that there is backwards compatibility between the two. While I understand that backwards compatibility is nice to have, looking at the parameters in the table, it does not exist between ACT and GMSL. Using “GSMLE” has thus to be considered as pure marketing. I therefore recommend to drop the GMSLE naming. If ACT was as good as it claims, why threaten the credibility of ACT (and everyone supporting it) with an association that it cannot hold? Furthermore, I think it conflicts with the IEEE code of Ethics.

Again, if you are convinced that ACT withstands the direct comparison to the TDD proposal, support the comparison effort with constructive input.

Kind regards,

Kirsten

Von: Matheus Kirsten, EE-352
Gesendet: Mittwoch, 28. Mai 2025 09:14
An: Ragnar Jonsson <rjonsson@xxxxxxxxxxx>; STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Betreff: AW: Invitation to the 802.3dm comparison study

Hello Ragnar,

I never ever responded to Amir’s question with “No, I would not change my mind whatsoever”, because that is against my beliefs. I might have said “No, this is not the point (meaning it is the wrong question), the comparison is not about me.” It is your misinterpretation that that means, I would not change my mind. I would kindly asked you to stop spreading such personal allegations on the reflector. I find that disrespectful.

Kind regards,

Kirsten

Von: Ragnar Jonsson <rjonsson@xxxxxxxxxxx>
Gesendet: Mittwoch, 28. Mai 2025 00:22
An: Matheus Kirsten, EE-352 <Kirsten.Matheus@xxxxxx>; STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Betreff: [EXTERNAL] RE: Invitation to the 802.3dm comparison study

Hi Kirsten, First, I look forward to getting answers to the questions in my email from Thursday. I would also like to encourage you and Gumersindo to update your presentation for New Orleans to match what was presented at the meeting. Gumersindo

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Hi Kirsten,

First, I look forward to getting answers to the questions in my email from Thursday. I would also like to encourage you and Gumersindo to update your presentation for New Orleans to match what was presented at the meeting. Gumersindo made important updates to the presentation to clarify that the intent with this work was not to bypass the 802.3dm Task Force.

Regarding your question about what I meant when stating “During the discussion on May 1st at least one supporter of this document stated clearly that the outcome of this document would not change their mind about TDD vs ACT”, I was referring to your answer to Amir’s question if you would be willing to change your mind about TDD and ACT/GMSLE based on the proposed effort. Your answer to this question was “NO” and you followed up with the question to Amir if he would change his mind. At this point, the chair stopped the discussion, but I asked Amir later and he told me that he is absolutely open to changing his mind if presented with convincing arguments (and that he also communicated this to you in a private email). I was not the only one taken back by your clear “NO” answer to Amir’s question, so thank you for clarifying that you are open to changing your mind and support ACT/GMSLE if presented with good arguments.

Ragnar

From: Matheus Kirsten, EE-352 <Kirsten.Matheus@xxxxxx>
Sent: Sunday, May 25, 2025 1:12 PM
To: Ragnar Jonsson <rjonsson@xxxxxxxxxxx>; STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] AW: Invitation to the 802.3dm comparison study

Dear Ragnar, in your email you are saying “During the discussion on May 1st at least one supporter of this document stated clearly that the outcome of this document would not change their mind about TDD vs ACT”. Who do you mean? There are only

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Dear Ragnar,

in your email you are saying “During the discussion on May 1^st at least one supporter of this document stated clearly that the outcome of this document would not change their mind about TDD vs ACT”. Who do you mean? There are only two supporters/authors on the document. Both Gumersindo and I can change our minds in the presence of good arguments. Any other interpretation of what has been said is a misunderstanding/misinterpretation.

Furthermore you write “I also heard at least one supporter of this document questioning if this document would change the mind of other individuals in the Task Force.” We sincerely apologize if more listeners had the same mishearing as you did. Part of what we believe makes a good engineer is the capability to change his/her mind in the presence of good arguments and we believe that the dm group consists of many very capable engineers. What would be the sense of striving for a comparison document otherwise?

Thank you for giving us the reason to clarify this to the group.

Kind regards,

Kirsten

Von: Ragnar Jonsson <rjonsson@xxxxxxxxxxx>
Gesendet: Donnerstag, 22. Mai 2025 18:52
An: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Betreff: [802.3_ISAAC] [EXTERNAL] RE: Invitation to the 802.3dm comparison study

Hi Gumersindo, Do I understand correctly that you are giving people 2-3 working days to send in “criteria deemed important”? Is this a hard cut-off date? I see that you talk about discussing “criteria fulfillment”. Can you please elaborate on

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Hi Gumersindo,

Do I understand correctly that you are giving people 2-3 working days to send in “criteria deemed important”? Is this a hard cut-off date?

I see that you talk about discussing “criteria fulfillment”. Can you please elaborate on what this discussion will output?

During the discussion in New Orleans, you clarified that this work would result in input into the Task Force and was not an attempt to circumvent the Task Force. However, I see that your presentation on the New Orleans meeting page has not been updated to reflect what you presented: https://www.ieee802.org/3/dm/public/0525/index.html. Can you please clarify who will be the target audience of this document? If it is the Task Force, do you believe that the Task Force lacks clarity on what it is trying to achieve?

How will disagreement be handled in in the discussion of this document? What kind of majority will be needed to put something into the document? Who makes the final call on what is in the output document?

In your list on slide 7 of the New Orleans presentation I see things like “Bi-directional use of ports”. In my mind it is obvious that we will have traffic in both directions on the link. Are you suggesting there that there should be a link that only goes in one direction, without any data flow in the other direction? Would you agree that this would be out of scope for the project?

Talking about things that are out of scope, in the Study Group there was majority support for including data rates above 10Gbps, but not the necessary 75% support for it. Would considerations about extending the data rates above 10Gbps be in scope for your document?

Like I said in the New Orleans meeting, I am not sure what the value of this document will be for the Task Force. I worry that this will be a distraction for the Task Force without delivering any tangible benefits. During the discussion on May 1^st at least one supporter of this document stated clearly that the outcome of this document would not change their mind about TDD vs ACT. I also heard at least one supporter of this document questioning if this document would change the mind of other individuals in the Task Force. If even the proponents of this document are saying that this document is not likely to change their mind, would it not make more sense for the Task Force to focus on its objectives?

Ragnar

From: Veloso Cauce Gumersindo, EE-352 <000045712ce4d5b2-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Thursday, May 22, 2025 7:50 AM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] [802.3_ISAAC] Invitation to the 802.3dm comparison study

Dear 802. 3dm participants, As announced on both the May 1st and May 16th 802. 3dm interim meetings, here are the details for the next steps on our joint comparison study. In the first step, we would like to agree on a list of criteria to address

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Dear 802.3dm participants,

As announced on both the May 1^st and May 16^th 802.3dm interim meetings, here are the details for the next steps on our joint comparison study.

In the first step, we would like to agree on a list of criteria to address before discussing the fulfillment of any criteria. In the attachment you find a PROPOSAL for the comparison criteria and their metrics. Please take careful look at them and evaluate if additional criteria or metrics are needed.
Send us your updated list (if any) until May 26^th EOB. We know this is short notice, however, this only identifies the criteria deemed important and not their fulfillment – for which we will then dedicate more time.
We start on May 28^th 15:00 CET with a Kick-Off meeting.

Introduce a proposal for the structure for the final document which shall result from our efforts.
Check on the collected criteria and discuss the collected input.
Next steps on the proposed items to elaborate fulfillment details.

Starting on June 4^th we would then initiate a weekly series till July 23^rd. Each week we discuss criteria fulfillment based on the incoming proposals shared with the group prior to the meetings.
Step by step completion/creation of the comparison document.

If you would like to participate in this meeting, please reply to either me or Kirsten (Kirsten.matheus@xxxxxx) and you will receive a dedicated meeting invite (Teams-Link) or just join with the following link at the dedicated time:

Jetzt an der Besprechung teilnehmen

Besprechungs-ID: 337 645 339 451 3

Kennung: 9XF9JW7a

You are welcome to send your input on the comparison items also if you are not able to join the meeting.

We are looking forward to your responses.

Thank you and best regards.

Gumersindo Veloso

P.s: For those not present at the last meetings, this is the motivation:

Currently, two technical proposals are competing within IEEE 802.3dm.
This documents aims to compare the two proposals and their rationales in order to provide an overview on the key properties and the different opinions on them.
It may serve as a “technically qualified overview at a glance” reference for individuals wanting to understand and form their own opinion.
The intention with this comparison document is

to clarify where there are agreements and disagreements.
to make the disagreements understandable.

This document

does not present a unified opinion.
does not favor one proposal over the other.

The authors prepare this document with the best intention to present an unbiased reference.

--
BMW Group
Gumersindo Veloso Cauce
EE-352

Systemfunktionen, Halbleiter, Vernetzungstechnologien
Max-Diamandstr. 5
80937 München

Postanschrift:

80788 München

Tel: +49-89-382-36389
Mobile: +49-151-601-36389
Mail: gumersindo.veloso@xxxxxx
Web: http://www.bmwgroup.com/

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