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Hi Rich, I would like to remind you of the analysis that I provided in https://www.ieee802.org/3/dm/public/adhoc/022725/jonsson_3dm_01_02_27_25.pdf This analysis shows that the probability of the worst-case cable impedance mismatch is extremely unlikely. In fact, my calculations showed that if 1% of cables would violate the impedance requirements, there
would still be over 400 years on average between observing the worst-case echo cable. A more likely scenario would be to have more than 4 trillion years between observing such cable. To put this into context, the earth is estimated to be just over 4 billion
years old. Four inline connectors are hardly ever used in real live in the industry. It is much more common to use one or two inline connectors, with some cases of three inline connectors. This will help reduce the echo
even further. In the discussion of my presentation, it was also pointed out that for a cable to stay within the +/-3Ohm across all temperatures, the allowed variation at any one temperature is much lower. It is reasonable
to assume that both cables coming together at a connector will have essentially the same temperature at the connector. Therefore, the impedance mismatch would be less than +/-3Ohm. I agree with you that it is possible to simulate very bad impedance mismatch, and I have even shared such bad cables with the group in https://www.ieee802.org/3/dm/public/0125/jonsson_3dm_01b_01_20_25.pdf This bad cable was last used in presentation by Ahmad and Mehmet in the New Orleans meeting: https://www.ieee802.org/3/dm/public/0525/Chini_3dm_02a_0525.pdf My experience also matches yours that I have not seen any real cables show this behavior. This is not surprising given how extremely unlikely such cables are (one every 400 years to 4 trillion years). The bottom line is very simple: Cables that come close to my simulated bad cable or what was proposed in the Zerna presentation you reference below are never seen in real live. These cables are unlikely to
be ever observed in real production, even if we wait for few hundred years. Ragnar From: Long, Richard J <0000451e32405de7-dmarc-request@xxxxxxxxxxxxxxxxx>
All, The topologies presented in https: //urldefense. proofpoint. com/v2/url?u=https-3A__ieee802. org_3_dm_public_0325_boyer-5Fsharma-2D3dm-5Fxx-5F03-2D10-2D25-5FRevB. pdf&d=DwIF3g&c=nKjWec2b6R0mOyPaz7xtfQ&r=hiHgBSUj2X0k3TORVxe0NCZAlJs6SEDHhwLDz5m9MbY&m=btumaWxPxcA9-QZm2r7ogJMswJHyKLYkKv6k4pj1kUN15hLKrRIeefAx9n55OyNZ&s=29tUat1fXLUxUggBnuHh2TRssCQ5amzXo2FrdD_UF0Y&e= All,
The topologies presented in https://urldefense.proofpoint.com/v2/url?u=https-3A__ieee802.org_3_dm_public_0325_boyer-5Fsharma-2D3dm-5Fxx-5F03-2D10-2D25-5FRevB.pdf&d=DwIF3g&c=nKjWec2b6R0mOyPaz7xtfQ&r=hiHgBSUj2X0k3TORVxe0NCZAlJs6SEDHhwLDz5m9MbY&m=btumaWxPxcA9-QZm2r7ogJMswJHyKLYkKv6k4pj1kUN15hLKrRIeefAx9n55OyNZ&s=29tUat1fXLUxUggBnuHh2TRssCQ5amzXo2FrdD_UF0Y&e= not being suitable for evaluation of RL limits is agreeable to me.
If you take a look at some of the past contributions, such as presented here for RL limits, see slide 11, the limits presented by Rich and Rohit would not pass:
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ieee802.org_3_dm_public_0724_Zerna-5F802.3dm-5F01b-5F240717-5FIL-5FRL-5FLimits.pdf&d=DwIF3g&c=nKjWec2b6R0mOyPaz7xtfQ&r=hiHgBSUj2X0k3TORVxe0NCZAlJs6SEDHhwLDz5m9MbY&m=btumaWxPxcA9-QZm2r7ogJMswJHyKLYkKv6k4pj1kUN15hLKrRIeefAx9n55OyNZ&s=562L611gpb4wJpwqkgdvKTW-AxCNpXjsfqLNCK2yWcg&e=
Here is another work with additional topologies presented that would not pass the limits proposed by Rich and Rohit:
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ieee802.org_3_dm_public_0924_bergner-5F3dm-5F01a-5F18-5F09-5F24.pdf&d=DwIF3g&c=nKjWec2b6R0mOyPaz7xtfQ&r=hiHgBSUj2X0k3TORVxe0NCZAlJs6SEDHhwLDz5m9MbY&m=btumaWxPxcA9-QZm2r7ogJMswJHyKLYkKv6k4pj1kUN15hLKrRIeefAx9n55OyNZ&s=X2Yh2NOjSyDFNIbnpCCney7MKJjuoEjDqmpW4s4BKs8&e=
Additionally keep in mind some of those topologies were created via simulation. So if you agree with those topologies, and the simulations, as being realistic then the RL limit should be relaxed. I would agree with something closer to what is presented by Zerna above.
Thanks.
-Rich Long
-----Original Message-----
From: Boyer, Rich <000012e205f410df-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Thursday, May 15, 2025 2:06 PM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_ISAAC] Questions on "boyer_sharma-3dm_xx_05-14-25_2.pdf"
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Hello Conrad,
This email is from Both Rohit and Rich. We both worked on this reply.
The reason the IL changed is that we are working to a compromise in 802.3dm as a new asynchronous technology of what is feasible from the IC transceiver and what is doable by links. Our goal is to find out what is doable within reason so that is why we work and collaborate with as many people as want to work together for good balance in transceiver technology and what may come in the future of links.
For the RL, we have evaluated many different realistic topologies from measured links. What we mean by "realistic" is from our experience of implementing complete links into vehicles. We realize that there maybe cases that do not meet in the <400 MHz and those cases need to be examined as to applicability and what could be done to make them meet.
We will put together a presentation for the next 802.3dm meeting and show RL data from some link topologies.
Best Regards,
- Rohit and Rich
-----Original Message-----
From: Conrad Zerna <conrad@xxxxxxxxxxxxxx>
Sent: Wednesday, May 14, 2025 4:19 PM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: [802.3_ISAAC] Questions on "boyer_sharma-3dm_xx_05-14-25_2.pdf"
CAUTION: This email comes from a non Aptiv email account Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi Rich, Rohit,
I was wondering about the specific reason, that the IL formula change from
Insertion loss(f) ≤ 0.0015 - 0.001325*f- 0.3785*√f - 1.1785/ √f (dB) in March to
Insertion loss(f) ≤ 0.0015 - 0.001325*f- 0.3645*√f - 1.1785/ √f (dB) now in May.
You said, it was due to "technology". What specific requirement/limitation of technology is that?
I also wanted to reiterate my comment from March, that the topologies in slides 3 here https://urldefense.proofpoint.com/v2/url?u=https-3A__ieee802.org_3_dm_public_0325_boyer-5Fsharma-2D3dm-5Fxx-5F03-2D10-2D25-5FRevB.pdf&d=DwIF3g&c=nKjWec2b6R0mOyPaz7xtfQ&r=hiHgBSUj2X0k3TORVxe0NCZAlJs6SEDHhwLDz5m9MbY&m=btumaWxPxcA9-QZm2r7ogJMswJHyKLYkKv6k4pj1kUN15hLKrRIeefAx9n55OyNZ&s=29tUat1fXLUxUggBnuHh2TRssCQ5amzXo2FrdD_UF0Y&e=
are not suitable to validate a proposed RL limit, especially in the lower frequency range.
If you have evaluated your new RL curve from May against other topology simulations?
Thanks,
Conrad
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