Re: [802.3_ISAAC] Presentation for the July Plenary

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Dear George, dear all!

Yes indeed, if the full frame does not fit into the TDD open time for the transmit direction in question, you need to store the remainder somewhere until the gate opens again. The same is true on the receive-side, where you need to reassemble the pieces that arrive in different time slices (here I disagree with Kirsten's slide on this). If you want to decouple the PHY from the upper layers, this buffer needs to be in the PHY (PHY as per the .3 model - not just the physical layer of the iso/osi model, which extends to above the MII). Or you expose the PHY schedule to the upper layers - what I show on slide 11. Btw, slide 11 is meant as a deterrent, not as a proposed solution. I don't think this is a good way to go, it may actually be more effort than putting a buffer in the PHY.

My base assumption in all of this is, that the MII will always only carry Full Frames, that entail (some) preamble, SFD, data, and CRC. I.e. you can not 'interrupt' the transmission of a Frame across the MII (RX or TX) by just inserting idle symbols somewhere between the preamble and the CRC. This is imho why preemption encapsulates the preemptable Frame fragments it creates into what the MII and PHY will see as full Frames, including all elements mentioned above without interruptions.

A full-duplex solution does not have this buffer issue, as the medium is always available. Or, as for EEE, the availability is at least not dictated by the PHY.

My main point is this buffer in the PHY or the avoidance of same in a non TDD system, as I think it will be in the order of 2 max. Frames, i.e. roughly 2x 1.5kByte. The discussions around "latency" or wait times may be a prequel to this, as I think the reason why we make the time slots smaller than a max. Ethernet Frame is vagule related to that timing discussion - and efficiency, and likely other stuff ...

I hope we now have a good basis for an informed discussion in Montreal.

Save travels all!

Best

Max

Max Turner, Dipl.Phys.

Automotive Network Architect

Ethernovia BV

Utrechtseweg 75

3702AA Zeist

The Netherlands

https://www.ethernovia.com/

c-de: +49 177 863 7804

c-nl: +31 685 386 449

On Thu, Jul 11, 2024 at 6:39 PM George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx> wrote:

Max – thanks for this update – your slides 9 through 11 point at the issues here that I am trying to wrap my head around – the relationship between the gate-open time and the ethernet frame size. It seems that you have to have an extra frame buffer either above the xMII or within the PHY to accommodate mismatch of an offered Ethernet frame to the PHY timing unless the frames are somehow synchronized to the gate time – and synchronizing to the gate time within the PHY would break layering… (I was thinking about this in regards to Kirsten & Kamal’s presentation on latency – dealing with that mismatch is an inherent additional buffer in a TDD system, I haven’t seen a way around it. You may argue it isn’t large, but I’m not seeing a way around the synchronization and the buffer needs to be accounted…)

As you say, the PHY doesn’t usually know about frames – I would say, the PHY isn’t supposed to know about frames.

Using something like preemption (e.g., clause 99 - which is defined when you have 2 MAC queues competing for the medium…) is an interesting notion for fragmenting a frame, but I would see this as just allowing a smaller maximum frame size. Is there something else here you are trying to communicate?

George Zimmerman, Ph.D.

President & Principal

CME Consulting, Inc.

Experts in Advanced PHYsical Communications

george@xxxxxxxxxxxxxxxxxxxx

310-920-3860

From: Max Turner <max.turner@xxxxxxxx>
Sent: Thursday, July 11, 2024 8:01 AM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_ISAAC] Presentation for the July Plenary

Dear all!

Thanks to everybody who took the time to look over my initial presentation draft and gave feedback. I took your input and questions to hopefully improve the presentation in terms of clarity and ease of understanding.

Here is an update to be presented next week.

Best

Max

--

Max Turner, Dipl.Phys.

Automotive Network Architect

Ethernovia BV

Utrechtseweg 75

3702AA Zeist

The Netherlands

https://www.ethernovia.com/

c-de: +49 177 863 7804

c-nl: +31 685 386 449

On Tue, Jul 2, 2024 at 9:31 AM Max Turner <max.turner@xxxxxxxx> wrote:

Dear all!

Please find attached my slides for the .3dm session during the July Plenary.

Feedback and questions up front are very welcome!

Best

Max

--

Max Turner, Dipl.Phys.

Automotive Network Architect

Ethernovia BV

Utrechtseweg 75

3702AA Zeist

The Netherlands

https://www.ethernovia.com/

c-de: +49 177 863 7804

c-nl: +31 685 386 449

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