I would agree that an existing standard, such as 40G, will not disappear. But a new standard, such as 400G, may never come to fruition. As you said before, there was a lot of initial opposition to the 40G standard, so now that we're debating 25 and 50 bit rates instead, my bet is that the emphasis on anything based on 40 will diminish.
The 4-lane Ethernets of today, that you mentioned in your post, aggregate to a powers of 10 bit rates. That was my point. That's why these 4-lane solutions use 2.5 or 25 or 250, not 4 or 40. For a 4-lane Ethernet to aggregate to anything else, like 400G, would be the novelty. I'm not sure why 802.3 membership would be pushing hard for such a choice. My bet is, they won't.
I'm not sure about the density argument. If 4*10G is high density, then wouldn't 5*10G be equally high density, and 2*25G be even higher density? We have to see what the vendors come up with, but my suspicion is that either 2*25G, or 1*50G, will beat out 4*10G, in terms of density, for anything in the 40G-50G speed range. And then you can aggregate these easily into 100G or eventually 1T bit rates.
As to physical layer signaling, I'm not sure why that would be dramatically different, between, say, the various PMD/PHY used for 40G, and new ones for either 25G or 50G.
The carrier arguments, i.e. carriage over SONET/SDH, were only to show that *a* motivation for 40G was that. A pre-existing SONET standard, available since 2001, immediately available for metro area Ethernets. But that rationale does not hold for 400G. So if the membership of IEEE 802.3 checks the potential SONET/SDH rates of the future, if that even matters anymore, they will notice that SONET/SDH will jump from 39.813 Gb/s to 159.252 Gb/s to 637.009 Gb/s, if we continue to increase the rate using the same sequence used to date. There is no 400G step in that sequence. Which means, you won't be using the entire concatenated SONET/SDH frame at 400G or 500G rates anyway. You'd have to use virtual tributaries to achieve such intermediate rates over SONET/SDH, and either 400G or 500G will just as easily pack into such VTs.
So bottom line, I'm not saying that SONET/SDH rates matter greatly anymore, nor am I a big proponent of such schemes. I am saying that SONET/SDH can't be used as *a* rationale for 400G, and do so in opposition to 500G, as it was at 40G. It's just as easy to easy to pick 500G as it is to pick 400G, if you insist on carrying these Ethernets over SONET/SDH.
The title of your post is dead-on - after our last exchange it is totally what i expect. While you are focusing on individual rates, your comment regarding x4 oddities is so not in sync with today's Ethernet environment. 40G is not going to disappear simply because we now have 25 or in the future 50G. Why? Because 4x10 GbE is enabling hhigher density solutions of 10G that before.
Also, if you go and look at the IEEE 802.3 Ethernet specifcation - you will mind multiiple instances of x4 configuration within the specificaiton - XAUI, Backplane, CX4, BASE-T, new 4Pair PoE, 100G, and now 400G.
I am guessing from your prior comments that you have more of a carrier emphasis. The Ethernet Alliance TEF is a great event to come and hear from different segments and learn what is really happening in each of the different segments. I would recommend you consider attending. SOme of the things you have said indiciate that this event would help provide you with some additional insight.
For more than a decade, Ethernet and optical transport has converged around a common set of rates (10G, 40G, 100G) which have facilitated interconnection of Ethernet over transport networks and advantages of common components for various applications. Evolving beyond these rates, modern optical networking gear based on complex, polarization multiplexed modulation formats with intradyne, coherent receivers tend to be DSP-based implementations which can often be programmed to support a variety of different modulation formats where the complexity of the constellation (number of bits per symbol) and the symbol rate can be selected based on the reach required for a particular link. There has been considerable discussion about how to provide efficient Ethernet-based router to transport interconnection in this more flexible optical networking environment.This panel brings together a group of distinguished experts representing cloud-scale data center operators, router manufacturers, optical networking equipment manufacturers, and component vendors. The panel will explore the merits of using flexible rates of Ethernet for router to transport interconnection, including configurations, use cases, and the implications for routers and transport gear.
All of the abstracts are up on line at the Ethernet Alliance website for your review.
@Bert: Good points. I sense there is already concern about having fractured the ecosystem.
Companies need to focus their investments. They once thought 40G made sense but now some are wondering if they can afford to make chips, cards, sw for 40G AND 50G.
There is some clear data center support from Google and Msoft as end users and their vendors for 25/50 now for a handful of reasons. As you point out that might push for a 500 not 400G standard, but the 400G effort is already embarked. Hmmmmmm
And, as I suggested quite recently, the same debate/question will no doubt occur with respect to 400G Ethernet, where 500G would be more in line with Ethernet traditional bit rates (in that it aggregates to a powers of 10 bit rate, which has always been Ethernet tradition), and performance-wise, well, what difference could it make?
The only valid excuse for the 4x oddities in the Ethernet lineup, only two of them in fact (40G and 400G), was simpler carriage over non-Ethernet physical media. If that non-Ethernet physical medium is either not used, or never existed at all (in case of 400G), why would these two rates survive? Once you have the 10/25/50 options available, one would expect the oddballs to be dropped along the way.
I don't think any of this is terribly earth shaking, mind you. Ultimately, users couldn't care much less, as long as the equipment is available at a decent price. This is mostly about tradition, IMO.