Re: [802.3_ISAAC] Link Delay - ACT vs TDD cable length

[Guy Hutchison <guy@xxxxxxxxxxxxxx>]

Hello Thomas,

The purpose of our group is to limit what the technology can do.  The goal of the group is to create a standard which is optimized for a particular purpose, not one that can be used for any application.

The group PAR is (emphasis added):
Specify additions to and appropriate modifications of IEEE Std 802.3 to add Physical Layer specifications and management parameters for electrical media and operating conditions optimized for automotive end-node camera links for operation up to 10 Gb/s in one direction and with a lower data rate in the other direction.

The resulting standard may very well be useful for agricultural, construction machinery, or even aviation and robotics.  However all of those applications are out of scope.

Regards,


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From: Hogenmueller Thomas (XC-CE/PAV-PRM1) <00000e1bea47ee01-dmarc-request@xxxxxxxxxxxxxxxxx>
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Subject: [802.3_ISAAC] AW: Link Delay - ACT vs TDD cable length

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Hello TJ,



Thanks for your clarification. We shouldn’t limit what the technology can do.



I also want to add that the potential market is also agriculture machinery and vehicles as well off-road machinery and vehicles (construction and mining). The term used therefore is called “Commercial Vehicle and Off-Road (CVO)”. These industries are making a tremendous transition to highly automation where video and raw-data radar sensors play an important role.



An industry that might also benefit from .3dm and longer reach are railway systems and any sort of public transportation.



Mit freundlichen Grüßen / Best regards

Thomas Hogenmueller




Von: TJ Houck <TJ.Houck@xxxxxxxxxxxx>
Gesendet: Montag, 10. November 2025 11:23
An: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Betreff: [802.3_ISAAC] Link Delay - ACT vs TDD cable length



Hi Scott,

Thanks for the presentation today. I want to address the recurring claim that longer-reach or higher-delay channels are “out of scope” or represent a market too small to justify inclusion. I think this characterization is inaccurate.



The OICA commercial-vehicle segment—which explicitly includes light-commercial vans, heavy trucks, and buses—represents tens of millions of vehicles globally each year. These platforms use camera and sensor links with harness lengths that can exceed 15meters and one-way delays of >90 ns, even in baseline configurations. These are in-scope automotive applications, not niche prototypes.



The IEEE 802.3dm PAR states “up to at least 15 m,” establishing a minimum, not a ceiling. Nothing in the PAR prevents support for longer channels when the insertion-loss and EMC budgets remain valid. Designing for only 15m assumes away real, measurable vehicle topologies already in production.



1. The technical issue remains unresolved

As Ragnar noted Relationship between TDD IBG <https://www.ieee802.org/3/dm/public/adhoc/062625/jonsson_3dm_01_06_26_25.pdf> , TDD proponents have not addressed the fundamental problem. Instead of reconciling this with actual vehicle geometries, the conversation keeps shifting to “market adequacy” (“few vehicles need longer runs”). That framing doesn’t eliminate the electrical risk. It only changes the topic.



2. The relationship between insertion loss and delay is being reversed. This is not a “delay-limit” problem but a channel-design problem.

The standard should not constrain insertion loss because of link delay — it should define insertion-loss first, and let the resulting delay follow from the physical channel.

When delay is capped at 90 ns, we are effectively forcing an arbitrary length ceiling, reducing the permissible IL margin for longer-body vehicles. The spec should instead allow full IL cable lengths.



3. Why 160 ns is the technically defensible number?

Automotive coax/STP VF ≈ 0.66 – 0.78 c (≈ 5 – 4.3 ns/m). Some cabling can be <0.66 velocity

160 ns ÷ 5 ns/m ≈ 32 m of cable reach or shorter cable with a lower Velocity factor cable.



This aligns with realistic routing in the upper end of OICA commercial classes (e.g., articulated buses ≈ 18 m, tractor + trailer ≈ 16 m + coupling ≈ 24–28 m effective path).

A 160 ns budget therefore covers the complete OICA “commercial vehicle” range — LCV, heavy truck, and bus — while preserving adequate guard margin for TDD turnaround, EMC filtering, and PoC filter delay.



4. Public data contradicts “15 m is enough”

Passenger cars already reach 12 – 13 m: Krieger (VW Group) presented Typical Automotive Harness Topologies to 802.3ch with 0.5 – 12.5 m total channel lengths for sedans/compacts. As stated earlier 15meters is the minimum, not the ceiling.



Long-body LCVs: adding roof-rail, high-roof A-pillar, cross-dash, service loops, and inlines yields ≈ 16 – 19 m which could lead to delays >90ns



Breakdown

  *   Roof-rail and pillar drop extension = +2-3meters
  *   Cross dash traverse = +1-2meters
  *   Service and door swing = 1-1.5meters
  *   Connectors – detouring = 0.5-1meter

Total additional over Sedan = 4-6meters = 16.5 to 18.5meters



Trailers/attachments:

  *   Van + car-hauler (16 – 24 ft) → 15 – 20 m total.
  *   Tractor + 53′ semi → 24 – 28 m continuous run.



Public references (all open):



  1.  Krieger – Typical Automotive Harness Topologies, IEEE 802.3ch (public, 0.5–12.5 m channels).

https://grouper.ieee.org/groups/802/3/ch/public/mar18/krieger_3ch_01a_0318.pdf

  1.  IndexBox – Trailer and Semi-Trailer World Market Overview 2024 (~11 M units).

https://www.indexbox.io/blog/trailer-and-semi-trailer-world-market-overview-2024-1/

  1.  Mercedes Upfitter Guidelines – Sprinter 170 Ext High Roof Video Harness Lengths (3 × 15 m).

https://www.mercedes-benz-vans.ca/content/dam/mb-vans/us/upfitter/220523_ARL_Sprinter_907_2022_ENU_fin.pdf

https://www.mbvans.com/en/upfitter/tech-info/bulletins



My goal in raising this is to ensure that the Task Force bases its delay assumptions on physical reality and scope definition, not on an unverified estimate of “market adequacy.”



Best Regards,

TJ Houck



Infineon Technologies Americas Corp. – Detroit

System Architect

tj.houck@xxxxxxxxxxxx<mailto:Joe.Bolsenga@xxxxxxxxxxxx>



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