Hi Gary,
All good comments, and a great exercise of quantifying transition to 100G LR4.
Which existing PMD to compare against proposed PMDs depends on which of the 802.3 Five Criteria we are addressing.
For 400G duplex SMF (2km and 10km reach objectives) we are determining Technical Feasibility. We have a lot of experience with 100GBASE-LR4, so it’s the right technical benchmark. Significantly harder specifications than LR4 raise a Technical Feasibility concern.
For 400G PSM4 (500m reach) objective, I had done the exercise of comparing against LR4 and all the proposed SMF PMDs are fine within the limitations of simple link budget analysis. (This assumed high coding gain FEC like BCH for 100G per lambda PMDs). The next step is to determine Economic Feasibility. CWDM4 uses KR4 FEC to significantly relax the TX and RX optical specifications therefore reducing cost, and will determine the 100G SMF market dynamics starting next year. This makes it the right economic benchmark. Significantly harder specifications than CWDM4 raises an Economic Feasibility concern.
When comparing Gen1 100GBASE-LR4 against a predecessor, the appropriate comparison is against 40G Serial OC768 (later became 40GBASE-FR), which was the highest speed existing optic at the time. Gen1 100GBASE-LR4 EML TX based specs. used OC768 optics as the starting point.
http://www.ieee802.org/3/bs/public/14_07/cole_3bs_02a_0714.pdf#page=5
Subsequent generation 100GBASE-LR4 DML based specs. used 10GBASE-LR as the starting point.
100G LR4 (EML) -OC768 (FR) specs. | 100G LR4 (DML) -10G LR specs. | 100G CWDM4 (DML) -10G LR specs. | |
TX OMA delta (pre-Mux) dB | -1.0 | 4.9 | 3.0 |
RX Sens. delta (post-DeMux) dB | -4.5 | -1.2 | 0.0 |
Total delta dB | 3.5 | 6.1 | 3.0 |
For EML based LR4 (Gen1), the relative receiver sensitivity is much harder than OC768. However, that had improved dramatically in the decade since the OC768 spec. was written (as can be seen in the receiver comparison column against LR). For the DML based LR4 (subsequent generations), the TX power is higher. This was not a major issue because some optical power has to be thrown away in 10G LR TOSAs to stay under the max. power limit.
The main take away point from the comparison is that the right use of DSP is to relax optical specifications as was done in going from LR4 to CWDM4. When DSP significantly increases the difficulty of the optical specifications, for example as seen in going from LR4 or CWDM4 to the 100G/lambda proposals in .bs, that seems like the wrong direction.
Chris
From: Gary Nicholl (gnicholl) [mailto:gnicholl@xxxxxxxxx]
Sent: Tuesday, September 30, 2014 2:55 PM
To: Ali Ghiasi; STDS-802-3-400G@xxxxxxxxxxxxxxxxx; Chris Cole
Subject: Re: [STDS-802-3-400G] Cole Presentation
Chris,
First thanks for pulling this presentation together. I may still be trying to get my head around all of the numbers, but it is the analysis that ultimately we all need (and need to agree upon).
I also like your comparison to existing 100G solutions . I think your intent here is to try and quantify the complexity/difficulty of the different 400GbE PMD proposals in relation to something that we are all familiar with, i.e. developing and delivering the first 100G solutions. I was about to make a point here at the end of the meeting but my phone died! The point I was going to make is that I think we should use the same basis for comparison for all of the 400G PMD objectives, i.e. 400G 500m PSM4, 400G 2km Duplex and 400G 10km Duplex. Using a common basis for comparison makes it possible to not only compare between different options within a single PMD objective, but also between solutions for different PMD objectives, i.e. how much harder is 2km duplex versus PSM4, or how much harder is 10km duplex versus 2km duplex, etc. With this in mind I would propose using 100G-LR4 as the basis for all comparisons. What we are investigating here are 1st generation 400GbE PMDs solutions and it makes sense to me to compare against a similar stage in the 100G project, i.e. the first generation 100GbE SMF PMD. Personally It doesn’t make a lot of sense to be comparing against a 3rd generation 100G-CWDM4 solution (and especially not for a single PMD objective, and then using 100G-LR4 for the others).
We next need to agree on how to interpret the comparison data. In your presentation you show ‘total delta dB’ numbers ranging from 1.5dB to 7.9dB. How do we interpret these numbers ? Is there a specific dB number (or range of numbers) we should be targeting for an optimal solution, below which we are not trying hard enough, and beyond which we are pushing the technology too hard ?
To provide some insight here I went back and tried to carry out a similar analysis for the transition from 10G-LR to 100G-LR4, to see "how hard we were pushing" when we choose 100G-LR4 as part of the 802.3ba project. The numbers I came up with are as follows (I encourage others to run their own analysis in case I made an error somewhere!):
Tx OMA delta (pre mux): 5.9dB
Rx Sen OMA delta (post demux): 3.9dB
TOTAL delta: 9.8dB
A delta of 9.8dB is significantly larger than for any of the 400GbE options on the table. Does this mean we were pushing the technology much harder for 100GbE than we are now for any of the 400GbE options? I suspect not. Perhaps it means that as we move to higher and higher speeds we are starting to pushing against some fundamental limits and extra dBs are harder to come by ? Bottom line is likely that while a comparison may provide a useful insight, but the devil is in the interpretation of the numbers.
Gary
From: Ali Ghiasi <aghiasi@xxxxxxxxx>
Reply-To: Ali Ghiasi <aghiasi@xxxxxxxxx>
Date: Tuesday, September 30, 2014 at 12:32 PM
To: "STDS-802-3-400G@xxxxxxxxxxxxxxxxx" <STDS-802-3-400G@xxxxxxxxxxxxxxxxx>
Subject: [STDS-802-3-400G] Cole Presentation
Chris
There was couple of questions on your presentation today
in regard what to use for optical Mux/De-Mux looking at couple of supplier Cubo, AFOP, Oplink indicate what you are using are reasonable
2 dB - 4 Channel Mux/De-Mux
3 dB - 8 Channel Mux/De-Mux
The AFOP CWDM 4 channel mux has loss of 1.5 and for 8 channel only 2 dB. Other suppliers losses are little higher, more in line with what you have 2 dB for 4 channels and 3 dB for 8 channels.
On slide 5 you referenced http://www.ieee802.org/3/bs/public/14_07/bhatt_3bs_01a_0714.pdf which has an error floor of 4E-4 for 106.25 Gb/s PAM4. Bhatt result were based on to be published ECOC paper M. Poulin.
However the published ECOC results are little worse than what was published in IEEE. Here are the BER results published in ECOC:
- 53 GBd PAM4 BER=2.9E-3
- 40 GBd PAM4 BER=2.4E-4
- 30 GBd PAM4 BER=1E-6
It looks like if you give PAM4 enough bandwidth as in the case of 30 GBd then BER improves and error floor improves.
