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Chris, I presume your questions are to the group since I have not made any proposals and only site what I have seen. My point is that both IMDD and coherent have more than one potential solution. We indeed have a lot of work to do. Jeff From: Chris Cole <chris.cole@xxxxxxxxx> [External Email. Be cautious of content] Hi Jeff, I fully agree with you that any PMD proposal will require demonstration of technical feasibility. The mildly rhetorical nature of your questions, suggests you are skeptical that technical feasibility for 800GbE-LR4 has been demonstrated. In an exchange with Mark last week, he also expressed skepticism though similar questions. Great
minds think alike. I am in agreement with both of you. Given that no 800GbE-LR4 proposal has been made, it’s hard to complete technical feasibility. Right now we are in the exploration stage, as can be seen from the wide range of ideas on the table, each
of them solving the major technical challenges in a different way. Your bring up of the CWDM4 grid is important because it should be in the mix. It has R&D advantages, interoperates with lower rates and FR4, and has negligible FWM. Just like at 400GbE we are not going to get 10km, so a similar exploration
of an acceptable lower reach is required. The one point I don’t understand is O-band. Hopefully we are past claims that a custom Coherent ASIC will be developed for LR. Therefore we have boat loads of Dispersion compensation. So why change the band to reduce Dispersion which doesn’t
need to be reduced, requiring new TX and RX optics, adding 2dB of loss, and losing interoperability with ZR? I am struggling to find a single benefit. Perhaps you can share one.
Chris From: Jeffery Maki <00000d5963b8071f-dmarc-request@xxxxxxxxxxxxxxxxx>
Chris, There is technical feasibility and market feasibility (size, cost and power). Have we proven 800G-LR4 is technically feasible? If made feasible, were there any new cost drivers to account for in the relative cost comparison? For example,
what is the cost of moving to a new wavelength grid some proposals advocate or implementation of polarization techniques? Wavelength grid was a major topic when we decided whether 100GBASE-LR4 should be on the CWDM grid or what we now know as LAN-WDM. Presentations
on these proposed technologies as cost drivers would be great to have for the comparison with coherent. Then for coherent, there is discussion of using O-band instead of C-band. What implications does this have? We need the best proposal for IMDD and coherent
with these cost assessments for the relative comparison. Jeff From: Chris Cole <chris.cole@xxxxxxxxx>
Dear Task Force Participants, During the 3/29/22 meeting, we started debating IMDD and Coherent alternatives for campus reach PMD.
In Transport, the debate was settled long ago as soon as feasibility of Coherent was established. It’s obvious that eliminating DCFs and reducing the number of EDFAs is a good idea. In Datacom, the CD, PMD and Sensitivity advantages of Coherent are not clear benefits, and Coherent is not an automatic choice. We have to do the hard work of analyzing technical and market trade-offs. Unfortunately, the 3/29/22 discussion
was not a good start, so a reset is in order. We know that when there is an FR interface, LR is not going to ship in the millions; it will ship in the tens of thousands. Similarly, we know that ZR interfaces don’t ship in the millions. Using LightCounting Vendor Survey Results through
Q4 2021, 100G/200G Coherent volume was ~½ million over the last five years, which is less than 2% of the 100G IMDD Datacenter volume over the same time period.
This means neither an IMDD nor Coherent LR solution will have a dedicated DSP ASIC. IMDD 800G LR4 will use the same DSP ASIC as FR4 and DR4, because these will ship in the many millions. Coherent 800G LR1 will use the same DSP ASIC as ZR
or ZR+ because those will ship in the tens and possibly hundreds of thousands. The IMDD DSP ASIC will be much lower cost than the ZR DSP ASIC because it’s volume will approach two orders of magnitude higher volume, like at a 100G. We don’t have to speculate
about the cost ratio of DSP ASICs at 800G; we have the answer at lower rates. The specs on IMDD LR4 optics are more stringent than FR4, which raises cost. The Coherent LR TX source doesn’t have to be tunable, which lowers cost. However this fixed laser is nothing like an IMDD source, it has to be cooled and held
to a precise wavelength otherwise it won’t match the RX LO. The most interesting argument in favor of Coherent is that if nothing is done, the standard ZR solution works for LR, without the need for another code. This has both R&D and OpEx advantages. Since the debate between IMDD and Coherent is likely to be replayed many times, let’s set a good example for the future by how we conduct it in .3df.
Chris From: John D'Ambrosia <jdambrosia@xxxxxxxxx>
All, Presentation material for our Task Force meeting on 29 March has been posted -
https://www.ieee802.org/3/df/public/22_03/index.html [ieee802.org]. Please note that Mr. Williams presentation has undergone legal review by IEEE legal. Mr. Law and I will provide guidance
regarding this presentation prior to Tom presenting, and ask that all comments are held to that time. As a reminder,
All interim teleconference meeting participants should review the following documents prior to participation in an interim meeting teleconference: ·
IEEE SA patent policy ·
IEEE SA Copyright Policy ·
IEEE SA Participation Policy All of these policies may be found at http://ieee802.org/3/policies.html
[ieee802.org]. Regards, John D’Ambrosia Chair, IEEE P802.3df Task Force To unsubscribe from the STDS-802-3-B400G list, click the following link:
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