| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
|
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 , 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
Total additional over Sedan = 4-6meters = 16.5 to 18.5meters Trailers/attachments:
Public references (all open):
https://grouper.ieee.org/groups/802/3/ch/public/mar18/krieger_3ch_01a_0318.pdf
https://www.indexbox.io/blog/trailer-and-semi-trailer-world-market-overview-2024-1/
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 To unsubscribe from the STDS-802-3-ISAAC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-ISAAC&A=1 |