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Re: [802.3_SPEP2P] compatibility between 100BASE-T1 and 100BASE-T1L



Matthias –

(first note – I am writing this as an individual offering my experience in PHYs, not as chair)

 

I would suggest that compatibility has (at least) three potential dimensions:

  1. Spectral compatibility – the two systems should not interfere with each other.  That is, when a link segment meets both the alien crosstalk coupling characteristics for 100BASE-T1 and 100BASE-T1L, each system should function in the presence of crosstalk from the other.
  2. Auto-Negotiation – systems that support autonegotiation should be able to negotiate to a commonly supported PHY type.  This is the normal way that different phy types achieve an operable link.  The standard doesn’t require support of both phy types in an implementation, and the market decides whether or not it is worthwhile.
  3. Interoperability of the phy types without autonegotiation – this matters when you don’t have autonegotiation, and hence, means that the 100BASE-T1L PHY must conform to all 100BASE-T1 specifications when the potential link partner is detected as 100BASE-T1 without the ability to support 100BASE-T1L (and, of course, the link segment supports).  For this to be the case, someone would need to offer detailed phy proposals and analysis that such a system would meet our objectives.

 

In my mind, the first 2 types are requirements. The first type is a requirement on the interference environments, and the second is covered by our objective #4 for support of optional auto-negotiation.

As to the third type of interoperability, that could be the subject of a phy proposal, and I would not want to see the phy proposal analysis preceded or short-cut because of some early-market, off-application use of 100BASE-T1 PHYs.

As an individual, I have personally seen several situations where technologies are sold into applications and installations that the phys were not designed for because “they worked” in early qualifications only to see that they did not stand up to the test of time and breadth of installation conditions.  Situations such as increased noise, aging, and the kinds of limiting specifications that we consider to and phy vendors design to are often not fully considered by such implementations and installations.  The result is a technology that does not scale, as even a small percentage of link failures can make for a problematic market environment.  Therefore, I’d (personally) hold a high burden of proof to the third type of interoperability above.

 

George Zimmerman, Ph.D.

President & Principal

CME Consulting, Inc.

Experts in Advanced PHYsical Communications

george@xxxxxxxxxxxxxxxxxxxx

310-920-3860

 

From: stds-802-3-spep2p@xxxxxxxxxxxxxxxxx <stds-802-3-spep2p@xxxxxxxxxxxxxxxxx> On Behalf Of Fritsche, Matthias
Sent: Tuesday, June 20, 2023 8:25 AM
To: STDS-802-3-SPEP2P@xxxxxxxxxxxxxxxxx
Subject: compatibility between 100BASE-T1 and 100BASE-T1L

 

Hello together,

 

I have a question to the group regarding the compatibility between 100BASE-T1 and 100BASE-T1L.

 

There is already a large amount of different PHYs for 100BASE-T1 on the market and the installed base outside vehicles is also growing. Publicly published test setups also show that today's 100BASE-T1 Phys can achieve more than 100m channel length. With the market introduction of 100BASE-T1L PHYs in the next few years, the question will certainly arise whether the 100BASE-T1 PHYs are or can be compatible with the new 100BASE-T1L PHYs? Will this be possible? I think that would be necessary from a market and user perspective.

 

Thanks for your feedback in advance

Very nice greetings and we see us in Berlin

Matthias

 

Best regards / Mit freundlichen Grüßen


Matthias Fritsche
HARTING Electronics GmbH
- Senior Specialist & Global Product Manager

Ethernet Connectivity -
Marienwerderstraße 3
32339 Espelkamp - Germany
E-mail:
Matthias.Fritsche@xxxxxxxxxxx
http://www.HARTING.com

 


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