| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
|
Hi
Tom
At this point, it is not possible to make fine technical distinctions between the IMDD and Coherent proposals and how they compare to previous generation technology. Neither is complete, and neither has demonstrated technical feasibility. If O-band is elected
for Coherent it will make the difference between LR1 and ZR far greater than the difference between LR4 and FR4.
My suggestion to both proponent Teams is focus on getting a solid, stable proposal in front of the Task Force. Avoid presentations like Mike's and Frank's because they don't add to our understanding. The Coherent Team may consider a bit more humility about
datacom optics and listen to experts like Ali and Arash who are cautioning about interoperability. The bold claims of link budget margin raise a concern that the Coherent Team is not even looking at this important issue.
For now, the ~2x cost ratio estimate is a reasonable place holder. We can refine it once we have two solid proposals in front of us.
From: Tom Williams (tjwill) <00001db419eaf3e1-dmarc-request@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, November 16, 2022 8:17 PM To: STDS-802-3-B400G@xxxxxxxxxxxxxxxxx <STDS-802-3-B400G@xxxxxxxxxxxxxxxxx> Subject: [EXTERNAL]: Re: [802.3_B400G] Task Force Chris,
One clarification on the relative cost information from my contribution in March. The 2.2x ratio was based on 1M cumulative shipments of each, so I did my best to normalize the volume effect. It’s true that the two products have different ramp patterns and, in fact, the LR was more expensive in lower volumes. This isn’t surprising because those lower volumes are more heavily weighted toward LR8 vs LR4, so these low volumes are not particularly meaningful for the current discussion. The long term volume forecasts for the two products are not so different to expect a dramatic change in the relative cost beyond the 1M parts shipped.
I believe there is credibility to my point that the gap should be less than this 2.2x number when we look at 800G LR1 vs LR4. 800LR1 would use lower cost laser technology than 400ZR and 800LR4 is less technically aligned with 800FR4 than 400LR4 is with 400FR4. I don’t think we’re claiming that the LR1 would be lower cost than LR4, but the difference is somewhere below the 2.2x starting point and task force members can make their own estimations by how much.
Tom
From: Chris Cole <chris@xxxxxxxxxxxxxxx>
Dear 802.3df Task Force Participants,
During yesterday's discussion, a number of misconceptions arose that need clearing up.
1. PMD Margin
In his presentation [ieee802.org], Mike Sluyski pointed out that the 800G LR4 IMDD proposal link budget margin is zero, and suggested this is bad. Unfortunately; all IEEE PMDs ever (with a couple of exceptions) have zero link budget margin, or more precisely unallocated loss. This may panic end users into shutting down their data centers, ripping out their optics, and replacing them with ones that have link budget margin. Fortunately, IEEE methodology picks the worst case PMD application corner, and defines a link budget that exactly meets it. The margin comes in other ways. Most optics are not deployed in worst case conditions, for example 10km optics operate over less than 10km. In modern manufacturing, IEEE spec. limits are several sigma out. There is margin for measurement uncertainty and other factors. So datacenter operators can be at ease. Despite all of their optics having zero link budget margin, the IEEE methodology is robust and their optics will continue to work just fine. Spoiler alert: a few optics fail in the field, which is a good thing, zero failures would be prohibitively costly.
2. Coherent Proposal
For months, we have been following the journey of exploration by the Coherent proponents, even though the 800G LR1 solution is obvious. It uses the ZR DSP and SiPIC, operates in C band, and replaces the tunable DWDM laser with a single lower performance fixed source. Let's see how many more detours will be taken before the return home.
3. WDM Grid CD
The 800G LR4 proposal is on the LWDM grid, which is tightly grouped near ZDW, and gives roughly 1/4 of CWDM4 grid CD. This is offset by doubling of the rate from 100G to 200G per lane. To first order, 400G LR4 (10km) has similar CD penalty as 800G LR4 (10km).
4. Relative Coherent vs. IMDD cost.
The best way to compare cost is using existing shipments. During the meeting, Tom Williams cited >2x cost ratio of ZR to LR4 (10km), which for a variety of reasons is an excellent proxy and a reasonable ratio. Right now, ZR volume is more than a magnitude higher than LR4 (10km) volume. We expect the ratio to fall over time. To first order, we can call the LR1 laser source savings washing out any cost ratio increase due to lower long-term volume ratio, giving a LR1/LR4 cost ratio projection of ~2x. All other relative cost advantage calculations by the Coherent and IMDD proponents are convoluted and unconvincing.
Thank you
Chris
On Wed, Nov 16, 2022 at 7:45 AM John D'Ambrosia <jdambrosia@xxxxxxxxx> wrote:
To unsubscribe from the STDS-802-3-B400G list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-B400G&A=1 [listserv.ieee.org] To unsubscribe from the STDS-802-3-B400G list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-B400G&A=1 To unsubscribe from the STDS-802-3-B400G list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-B400G&A=1 |