Re: [802.3_100GNGOPTX] Emerging new reach space

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On Nov 21, 2011, at 2:33 PM, Daniel Dove wrote:

Hi Ali,

I am a proponent of the "Show me the data" approach to setting objectives.

Rather than hypothesize about how various methods can be used to achieve various lengths, I would like to see something more specific, and then from the data determine if there are natural cut-off points where any particular choice of solutions can support an objective that has market potential.

We are in a Study Group, so solutions are not important beyond their ability to demonstrate Technical Feasibility, Economic Feasibility, and Market Potential.

I have specifically asked for a chart that shows two general pieces of information. (MMF reach)

A break down of media reach in existing Server/Switch and Switch/Switch applications. (Paul has provided this)
Relative cost of key functional blocks needed to achieve any particular reach within the ranges provided in #1 above.
I think this is where we need to go to answer the question of MMF reach, and perhaps whether one PMD for MMF will be sufficient.

What we need are relative costs of the key functional blocks being discussed like FEC, VCSEL performance levels, equalization, or any other items that would help achieve any particular reach. When we discuss relative cost, I think power is also of interest as it has a cost element and density impact.

If the various cost elements were broken out as shown, and we saw that to achieve 100m the cost would be 3x the cost of 30m, and that we can satisfy 92% of the server/switch links with that lower cost solution, it might lead us to consider a separate PMD for server/switch links. On the other hand, if the cost differential between 30m and 100m was only a few percent, a totally different outcome can be drawn. As I said, understanding the power dissipation of the alternatives would also be useful to see if there are break-points in the power curves.

Can we get the relative power and cost for various methods to achieve the reaches shown in Paul's distribution charts?

Dan

From: Ali Ghiasi <aghiasi@xxxxxxxxxxxx>
Reply-To: Ali Ghiasi <aghiasi@xxxxxxxxxxxx>
Date: Mon, 21 Nov 2011 11:55:48 -0800
To: 100G Group <STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Hi

I like to expand this debate to include reach objective for 100G-SR4. Currently defined 40Gbase-SR4 has reach of 100 m on OM3 or
150 m on OM4. Due to current cost and availability of 40Gbase-LR4 the 40Gabse-SR4 links are pushed to their full limit and sometimes
even beyond.

While we are in the middle great debate toward a objective for SMF PMD while not knowing how many lanes, wavelength, or signaling but
we know 100G-SR4 will have 4 lanes and the signaling will be NRZ. There where several presentation in Atlanta touching the reach objective
-pepe;iugoski_01_1111 suggest HPC could be served with 20-30 m possibly have two PMD one with 10 m reach another with 50-70 m reach,
also CDR and EQ adds too much power to the module

- king_01_1111 suggest 70 m without FEC and 125 m with FEC on OM4 fiber, the assumed Tr/Tf at least the fall time of 20 ps it was suggested
the fall time would be more like 25 ps

- ghiasi_01_0111 showed that 100G-SR4 link will be dominated by VCSEL slow fall times even at B2B the WDP penalty was ~2.5 dBo and
at about 120 m of OM3 fiber the penalty is increased by just 1 dBo. An equalized link at 120 m of OM3 will have less penalty than B2B link.
With suggestion to maintain 40G-SR4 reach of 100 m on OM3 or 150 m on OM4.

Petar seems OK with even 20-30 m but at absolute lowest power for HPC applications without retimer or EQ in the module. I expect a traditional
limiting interface even at 20-30 m reach could fall apart due to VCSEL and host penalty. FEC could possibly be a solution but I doubt it will be
acceptable within HPC environment. At 100 m (OM3) or 150 m (OM4) fiber is not the dominant source of penalty but sacrificing the fiber is the
easiest thing to do at modest improvement of the link penalty.

I believe we can meet Petar request for low power and offering full 100(OM3) /150 (OM4) m reach by one PMD if paired with simpler host it offers the
lowest power and when paired with more capable host offers full reach. This could be similar to concept of linear and limiting interface in SFP+.
Some may even dispute if this can be done for 25G so lets set a side technical feasibility for Newport Beach. For now lets focus what should
100G-SR4 reaches be:
- 20 m on OM3 or 30 m on OM4
- 50 m on OM3 or 75 m om OM4
- 70 m on OM 3 or 100 m on OM4
- 100 m on OM3 or 150 m on OM4 (current 40GBase-SR4 cable plant)
direct inputs from OEMs, end users, or cable installer is highly desired.

Thanks.
Ali

On Nov 21, 2011, at 8:44 AM, Chris Cole wrote:

Hi Pete,

1)      My impression was that Matt’s proposal was more general than for a 600m or 1000m reach interface. Since he is on the reflector, he can clarify what he meant.
2)      Sadly, you are exactly correct here to point out that a fully standard compliant interface could have the same max TDP at 10km and at 2km. This is actually not even contrived as positive dispersion helps DFB penalties below 1310nm. So sadly once again you have dashed our hopes of getting a free lunch. If we want to specify an alternate operating point, with a higher dispersion loss at lower reach, we would have to add a normative specification with a lower TDP at the shorter reach. L

Chris

From: Anslow, Peter [mailto:panslow@xxxxxxxxx]
Sent: Monday, November 21, 2011 7:51 AM
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Chris,

1)      This thread seems to be wandering somewhat off topic. For the relatively short reaches that have been proposed on this thread, there wouldn’t be much reach related optical penalty to trade for loss if the reach was shorter still.

2)      For 100GBASE-LR4 the maximum loss of the link is not informative. 87.11 starts: “The 40GBASE–LR4 fiber optic cabling shall meet the specifications defined in Table 87–14”. Table 87-14 includes:
“Channel insertion lossa, b(max) 6.7 dB”
“aThese channel insertion loss values include cable, connectors, and splices.”
“bOver the wavelength range 1264.5 nm to 1337.5 nm.”

Also, the effective TDP is allowed to be as low as 0.8 dB for a device with a low spectral penalty, so you cannot rely on the transmitter having spare power above the 6.7 dB channel loss unless the TDP is significantly more than the minimum allowed.

Regards,
Pete Anslow | Senior Standards Advisor
43-51 Worship Street | London, EC2A 2DX, UK
Direct +44 2070 125535 |

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From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: 21 November 2011 14:55
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Hi Paul,

Good question. It is not yet in standards, but rather it is an example of an entry in the informative table that Matt proposed we add to future standards.

Specifically, the 100GE-LR4 link budget is 8.5dB, of which 6.3dB is loss budget which can be used in a variety of useful ways like going over SMF or through passive loss elements like path panels or cross-connects. There is also a 2.2dB allocation for penalties. That is one use scenario. The example I gave shows another use scenario. If an end user only needs a 2km reach, they have available in round numbers,~7dB of loss budget. Obviously if we were writing these numbers into the standard, we would be more precise.

Keep in mind that link budget itself is informative. The normative specs are TDP and SRS. So Matt’s proposal to add an informative link budget table is entire consistent with how we handle the single link budget entry today.

Chris

From: Kolesar, Paul [mailto:PKOLESAR@xxxxxxxxxxxxx]
Sent: Monday, November 21, 2011 5:29 AM
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Chris,
Can you cite the location of the 2km / 7dB information in the standard? I only find information on 30 km vs 40 km engineered link for –ER4.
Paul

From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Sunday, November 20, 2011 3:31 PM
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Matt,
Adding an informative table in future standards on reach vs. loss budget trade-off is an excellent idea. Many end users do this implicitly already, so they will benefit by having more exact numbers from those that write the standards.
For 100GE-LR4, this type of information is already informally provided, for example pointing out that for shorter reaches like ~2km, a ~7dB loss budget is available.
Chris
From: "Matt Traverso (mattrave)" <mattrave@xxxxxxxxx>
Date: November 20, 2011 12:36:21 PM EST
To: John D'Ambrosia <jdambrosia@xxxxxxxxxxxxxxx>, "STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx" <STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx>
Subject: RE: [802.3_100GNGOPTX] Emerging new reach space
Colleagues,

John wrote: "Also one lesson that we should learn from recent industry debates -forget the reach- what is the desired budget?"

As Chris Cole & others have pointed out, the reach is dependent upon the transmission penalties as well as the link budget -- see discussion on wavelength pitch. It might be a useful approach to consider trading off a scenario where the amount of additional insertion loss (connectors, splices etc) versus distance.

For example, we could set an objective of 1km with 2dB of insertion loss (no significance -- I just pulled it out of the ether). Then we could provide an informative table which could highlight at 500m reach the allowable insertion loss is 2dB + X. Alternately, we could provide a scenario which shows that if the insertion loss is only 1dB then the reach is 1km + Y.

On the HSSG reference, I believe it was Ted Seely coming to the microphone to object to the presentation Chris, Eddie & I put together (http://www.ieee802.org/3/hssg/public/nov07/cole_01_1107.pdf) -- he was concerned that there were many scenarios where there were higher connectors/insertion loss such that he preferred 10km to accommodate the additional insertion loss.

cheers
--matt

-----Original Message-----
From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxxxxxxxx]
Sent: Saturday, November 19, 2011 12:27 PM
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Paul
I notice you used a city block but you did leave out the fact that it was a multifloor scenario.

However as I pointed out I remember this from hssg days which is 5 years ago. I agree with the call for new data and am not sure what data that has been presented to the IEEE that details the industry 2km need. How much of that is want and not need is unclear to me.

Also one lesson that we should learn from recent industry debates -forget the reach- what is the desired budget?

John

Sent from my iPhone

On Nov 19, 2011, at 2:16 PM, "Kolesar, Paul" <PKOLESAR@xxxxxxxxxxxxx> wrote:
Scott,
I agree with the thrust of your assessment.

A minor correction. I did include the entire link distribution in my analysis. The only truncated input in my analysis is the patch cord distribution above 70 ft. The percentage of channels within (or above) any length is the result of convolution of the length distributions of constituent links and cords, which carries the probabilities with it. For example, if 10% of links lie above 100 m, the probability of two concatenated links being longer than 200 m is 0.10 x 0.10 = 1%. This is over simplified because it does not include the equipment cords and the patch cord that create full channels.

I note that your cut-off at 400,000 square feet allows for a square footprint that is 632 feet on a side, substantially bigger than a square block which, at one tenth of a mile on a side, is 279,000 square feet.

Paul

-----Original Message-----
From: Scott Kipp [mailto:skipp@xxxxxxxxxxx]
Sent: Saturday, November 19, 2011 11:59 AM
To: STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GNGOPTX] Emerging new reach space

Jeff,

I agree with your point about distributions.

No, it was not arbitrary that I stopped at 400,000 sq ft. I stopped at 400,000 sq ft because I wanted to cut off the tail of the distribution of the size of the data centers. I propose that there are only a few % (probably les than 1%) of data centers that are over 400,000 sq ft. The larger ones are the mega data center or massive data centers (MDC in either case) that Google and others are deploying.

Google is a very interesting case study since they deliver over 6% of all Internet traffic. I just got a response from Bikash and he says they do have 2 km links and he is getting frustrated with the IEEE second guessing this reality. What I think we need to do is understand that the MDC market has atypical needs and we do have solutions for this with LR4, 10X10-2km and 10X10-10km.

I suggest that we have a bifurcation in the market where we have what most people do and we have what the MDCs do. One piece of data on this is in Paul Kolesar's data where he shows over 5% of permanent links between patch panels in 2010 are over 119 meters long (see slide 8 ofhttp://www.ieee802.org/3/100GNGOPTX/public/sept11/kolesar_02_0911_NG100GOPTX.pdf). Paul did not include these outliers in his analysis that shows only 1% of links are over 256 meters long (cell R31 of the Kolesar Kalculator). We need to understand what assumptions and limits we're putting on the data since this affects our conclusions.

I will present on this more in Newport Beach. I have gone to some large data centers, but not MDCs because they won't let people like me in! We need to make the distinction between the white space (the raised floor where equipment resides) and the building size of the data center. The white space is a significant subset of the building size. The white space can be separated by significant distances and this can lead to long permanent links between the white space.

I'm proposing that the nR4 solution would meet the needs of many links that are longer than SR4. From the Kolesar Kalculator, 19% of links are longer than 100 meters and less than 256 meters (cells R14-R31). 19% of links would need nR4 or LR4 if SR4 only supports 100 meters.

If SR4 matches the 150 meters of SR10 which will be very challenging with 25G lanes, then the nR4 market would shrink to about 8% of links (cells R19 to R31). Paul told me that the 2:1 mix is the most likely deployment scenario in the industry and corresponds to column R in the spreadsheet. Only 1% of links are longer than 256 meters according to Paul's work.

I hope that helps,
Scott

-----Original Message-----
From: Jeffery Maki [mailto:jmaki@xxxxxxxxxxx]
Sent: Friday, November 18, 2011 5:05 PM
To: Scott Kipp; STDS-802-3-100GNGOPTX@xxxxxxxxxxxxxxxxx
Subject: RE: [802.3_100GNGOPTX] Emerging new reach space

Scott,

Was the choice to end your table at 400,000 sq. ft. arbitrary?

All,

I believe we need to know if the potential square footage may or may not grow larger over the coming years for what is known as a mega datacenter. How big is a mega datacenter to be? At some point, 100GBASE-LR4 will be the right choice just based on loss budget. We need to know the distribution of reaches to understand where to draw the line in selecting a break in the PMD definitions.

[snip]