Re: [STDS-802-3-400G] 答复: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

[Vipul Bhatt <vbhatt@xxxxxxxxx>]

Picking up a sub-thread here, I want to express my support for the views of Chris and Helen. We are better off approaching 100G as 2x50G than as DR4 divided by 4.

In yesterday's ad hoc call, we discussed work partitioning of 50G/100G/200G -- how to combine efforts, avoid schedule delay, simplify editorial challenges, etc. All well and good. However, our bigger obligation is to write specs for a successful standard. The success of a standard is gauged by how widely it is adopted in the market, not by how efficiently we manage the IEEE process. Widespread adoption happens only if per-port cost of an Ethernet solution is competitively low. In practical terms, this boils down to enabling low-cost optics. Therefore, our partitioning decision should be subservient to the goal of achieving the lowest cost of optics, not hinder it. (If we can align the two, all the better.)

To achieve low-cost optics, the biggest lever we have is extensive re-use of 50G (25 GBaud PAM4) optics -- Nx50G, where N can be 1, 2, and 4. The case of N=1 will provide a huge volume base that the component ecosystem can amortize cost over.

Why not use Mx100G where M can be 1 and 2? Wouldn't 100G (50 GBaud PAM4) optics be lower in cost because it uses only one wavelength? No, not yet, despite it being a seductive idea.

Since the .bm days, some colleagues (including me) have been drawn to the idea of single-wavelength 100G. Later, as I supported all three .bs baselines (FR8, LR8 as well as DR4), I had an opportunity to look more closely at both 25 GBaud PAM and 50 GBaud PAM4 product development. My view is now more balanced, from a technical as well as economic perspective.

50 GBaud PAM will certainly have its day in the sun. We will see that day arriving in the form of reports of improving and real measurements at leading edge conferences like OFC and ECOC.

But in IEEE, we should write specs based on performance we can prove. For broad market success, 50 GBaud PAM still has several hurdles to cross -- design, packaging, signal integrity, yields -- with no immediate timeline in sight. Some may claim to cross these hurdles soon, and that's great, but that's not the same thing as broad supplier base.

It is one thing to show a forward-looking lab result; it is quite another to have manufactured components that give us characterization data we can use for developing PMD specs with correctly allocated margins. From that perspective, we are on more solid ground with 25 GBaud PAM than with 50 GBaud PAM. Let's walk before we run.

The DR4 argument -- "We voted for DR4 in 400G, so let's carry the underlying risks and assumptions forward" -- sounds like unnecessarily doubling down on an avoidable risk.

With best regards,

Vipul

Vipul Bhatt
vbhatt@xxxxxxxxx
+1 (408) 461-8521 mobile

On Thu, Dec 3, 2015 at 7:25 PM, Xuyu (Helen) <helen.xuyu@xxxxxxxxxx> wrote:

I agree with chris’s point. 100G single lane is one of important solutions for future research and need solid work. Including this to bs will bring an expected debate and delay.

 

发件人: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
发送时间: 2015年12月4日 4:33
收件人: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
主题: Re: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

John

My position on 100G single wavelength is that it belongs in a future Study Group, will require substantial technical contributions, and will cause a substantial technical debate. This is incompatible with addition into an existing project like 802.3bs, unless we are willing to completely reset the schedule.

 

Further, given the broad and substantial research effort into 100G single wavelength by the optics industry, it is best for 802.3 to let those efforts play out, and not engage in more crystal balling. 802.3 is not the best place to first report and debate fundamental research results. The right place for this are refereed journals and technical conferences.

 

Chris

 

From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxx]
Sent: Thursday, December 03, 2015 12:19 PM
To: Chris Cole; STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: RE: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

So you are saying do something different than what is agreed upon for dr4? 

 

From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Thursday, December 3, 2015 3:16 PM
To: John D'Ambrosia <jdambrosia@xxxxxxxxx>; STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: RE: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

John,

 

100GBASE-DR implies nothing about modulation format. It simply designates a single lane 500m interface. Modulation would be selected based on technical and other merit. Compatibility with a 4x standard would be a consideration but hardly an overriding one.

 

Chris

 

From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxx]
Sent: Thursday, December 03, 2015 11:58 AM
To: Chris Cole; STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: RE: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Chris,

Yes I am – anything differing than what is being done in .3bs will add delay – but your assumption was not clear from your use of 100G-DR nomenclature. 

 

However, it seems to me that there is a hard argument to use something different for a single lane approach than what is used for a x4 lane approach. 

 

John

 

From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Thursday, December 3, 2015 2:53 PM
To: John D'Ambrosia <jdambrosia@xxxxxxxxx>; STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: RE: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

John,

You are making the assumption that if we are to have single wavelength 100G, the right answer is 50GBaud PAM4. This is unsupported either by measurements or by research results.

 

We are once again reminded that trying to predict the future by more than one technology generation ahead is a low probability of success activity and therefore should not be done in standards bodies.

Chris

 

From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxx]
Sent: Thursday, December 03, 2015 11:47 AM
To: Chris Cole; STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: RE: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Chris,

I am not getting your point here – how are we introducing further delay?  We already have DR4 in the 400G standard.  What additional delay will there be to just have a single lane implementation?

 

John

 

From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Thursday, December 3, 2015 2:42 PM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Hi Steve

 

One reason we may not want to do 100GBASE-DR in 802.3bs is to not add considerably delay to the 802.3b schedule while we debate the merit of supporting measurements. And given the research results we are seeing presented in recent technical publications and conferences, we are sure to see the modulation debate re-opened, which is an even better prescription to delay 802.3bs schedule.

 

Chris

 

From: Trowbridge, Stephen J (Steve) [mailto:steve.trowbridge@xxxxxxxxxxxxxxxxxx]
Sent: Thursday, December 03, 2015 10:39 AM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Hi Chris and Rob,

Just to play devil’s advocate here, I think it depends on the objectives agreed in the study group.

If the only stuff we have objectives to do for 200G are the same things we are doing at 400G with fewer lanes, sure, it all folds right in to P802.3bs. Specifically:

We would specify 8-lane CCAUI-8 and 4-lane CCAUI-4 C2C and C2M interfaces.

We would specify 200GBASE-SR8, 200GBASE-DR2, 200GBASE-FR4, and 200GBASE-LR4 PMDs.

But the flies in the ointment would be if we have objectives to build a 200GBASE-SR4, 200GBASE-CR4, or 200GBASE-KR4 PMD, which I think would be quite challenging on the current P802.3bs schedule.

 

Presumably the reason you think 100G belongs with 50G is that you assume this project needs to do interfaces like 100GBASE-SR2, 100GBASE-CR2, 100GBASE-KR2. But why wouldn’t you do, for example, a 100GBASE-DR interface in the P802.3bs project?

Regards,

Steve

 

From: Rob (Robert) Stone [mailto:rob.stone@xxxxxxxxxxxx]
Sent: Thursday, December 03, 2015 11:10 AM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Chris I agree with your observation, and I have been thinking the same thing with respect to the partitioning of the work.

 

It would seem that if possible, using the KR4 FEC for 50 and 100G would have a lot of benefits with respect to compatibility with existing MAC rates and 25G based technologies. I would expect that it is likely we will see co-existence of 25 and 50G / lane technologies within the same environment, and if so we should make an effort when defining the logic to enable straightforward low power connections between the different generations. Using end – end KP4 FEC would help facilitate that.

 

Thanks

 

Rob

 

From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Thursday, December 03, 2015 8:53 AM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

The idea of rolling 200G into the 400G project is compelling. In prior discussions, we had rejected this as too late for 802.3bs TF, so it’s encouraging to see we are willing to revisit. One mental test of why this makes sense is to consider what we would have done in 400G Study Group if we knew what we know now. Given the CFI support, it could be argued that most people would have supported both 200G and 400G. If anything, 200G is more compelling.

However, the inclusion of 100G in the 400G project is much less clear. Several arguments can be made that it more naturally belongs in the 50G project. An important consideration is that for both 50G and 100G, backwards compatibility with existing 25G I/O interfaces is important. Specifically we will want 50G supported with 2x25G electrical I/O and 100G to be supported with 4x25G I/O (CAUI-4). This suggests that for 50G single wavelength and 100G WDM2 solutions, KR4 is the appropriate FEC. For both, this gives reasonable optical margin with PAM4 modulation. On the other hand, for 200G WDM4 KP4 is a better choice, same as for 400G WDM8.

Adding only 200G to the 400G project makes for much cleaner documentation modification. Broad market potential for 200G is the same as for 400G. We don’t need to introduce new justification which is required for 100G. Not having 100G, removes any dependence on any other project, so there is no need to discuss this.

 

Chris

 

From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxx]
Sent: Thursday, December 03, 2015 6:00 AM
To: STDS-802-3-400G@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-3-400G] New 50G/100G/200G SG - Potential Impact on 802.3bs?

 

Dear Task Force Participants,

This email is to make sure that everyone is aware of conversations happening in the 50/100/200G Study Group Phone Conference that happened yesterday – Dec 2.  There has been discussion at how the multi-lane 100G/200G solutions might be rolled into the 802.3bs project.  To that end – I gave a presentation at the conference call that looked at potential modifications / additions to our PAR / CSD.  See http://www.ieee802.org/3/50G/public/adhoc/archive/dambrosia_120215_50GE_NGOATH_adhoc_v2.pdf

 

I encourage everyone to review this presentation and consider the findings on the last few pages.  Individuals may wish to participate in the upcoming 50/100/200G ad hoc calls that Mr. Nowell has planned.  For more information see http://www.ieee802.org/3/50G/public/adhoc/index.html.

 

I will be working on the meeting announcement for the January interim, and anticipate that there will be a joint session of our Task Force with the Study Groups to further consider these implications.

 

Regards,

 

John D’Ambrosia

Chair, IEEE P802.3bs 400GbE Task Force