Books 2020: Part II
Gazettabyte asks industry figures to pick their reads of the year. In Part II, Maxim Kuschnerov, Professor Roel Baets and Yves LeMaître share their favourites.
Maxim Kuschnerov, Director of the Optical & Quantum Communications Laboratory, Huawei
Beyond Weird: Why Everything You Thought You Knew about Physic is Different by Philip Ball is one of my favourite books about physics. It offers an intuitive and math-free view on the beauty of quantum mechanics, which, in its approach, is almost philosophical.
As the author states, one of the problems that people have with the inherent unpredictability of quantum effects is the lack of analogies from real life that would make quantum phenomena relatable.
Although I didn’t last four weeks on my quantum course at university due to the mathematics, I find my world full of quantum analogies. As planners, we always need to think about a running project in terms of the possible outcomes mitigating future risks until the deliverables materialise. Also, it’s clear to every marketing person that a product’s success is partly due to its features and in part (and maybe even more so) due to customer perception. So, in that sense, one should be puzzled that observation changes the state of a quantum system .. or the next smartphone’s success.
John Bolton’s The Room Where It Happened: A White House Memoir provides an open view into the daily work of President Donald Trump and his security advisors. It’s surprising that seemingly solid and experienced advisors like Bolton still act like it’s the 1980s and, en passant, suggest to bomb North Korea. While Bolton dedicates himself to criticising a still-sitting president, he is a relic and one should be glad that he is no longer in politics.
After binge-watching The Last Dance, the 10-part Michael Jordon documentary during the first lockdown, I ordered the legendary book from the 1990s, Jordan Rules, which described the tough, win-at-all-costs persona of a then young Michael Jordan.
Having discovered that the only copy of this book that I found and ordered on Amazon was in Polish (yikes!), I settled for the next best historical basketball account of how Larry and Earvin “Magic” Johnson made basketball into primetime television in the 1980s.
Larry Bird and Magic Johnson’s book When the Game Was Ours is a joint biography by two formerly bitter rivals. It provide a compassionate view of their relationship, which saw Magic call Larry to inform him about being HIV positive before telling the press, a reflection of the respect the two competitors held for each other.
Chris Voss’s Never Split the Difference: Negotiating As if Your Life Depended On It is a true highlight for all the occasions in life where you need to make a deal. This is a highly psychological book, what is required is to develop a deep sense of empathy for the other party as a foundation for any agreement. And if the author can negotiate with terrorists and bring the ransom down by two orders of magnitude, this book should prepare you well for your next salary review.
Professor Roel Baets, director of the multidisciplinary Centre for Nano- and Biophotonics at Ghent University, Belgium.
Two books, both non-fiction, impressed me a lot in 2020. The first is Humankind: A Hopeful History by Rutger Bregman. I read both in Dutch but one English translation exists and the other is coming next year. Bregman’s book is thought-provoking. The second book, Bart Van Loo’s The Burgundians: The Vanished Empire is history narrated in a sublime way.
Yves LeMaître, president of Rio Lasers, an Optasense business.
Well, I guess there is always a silver lining. The new working-from-home COVID world allowed me to discover more books than I had in ages, turning the daily mindless and soul-destroying commute on Highway 101 into an opportunity to learn about California and US history.
Let me start with Junipero Serra: California’s Founding Father by Steven W. Hackell. From his statue pointing an accusing finger at me on my drive to San Francisco to his name present all across California missions, streets, cities and schools, Father Serra is hard to ignore. I had heard about his critical role in the first Spanish expedition into Alta California in 1769 and establishing the Mission system but knew little beyond that.
Serra became a highly controversial figure due to his role in creating a system that fostered harsh repression of Native American cultures. Serra was canonized in 2015 and is one of the two Californians selected to represent the State in the US Capitol Statuary Hall, the other being Ronald Reagan. As part of the 2020 cultural and social debate surrounding historical figures and their roles shaping race relations, the biography by Steven Hackell could hardly be more relevant and is a must-read to get a deeper understanding of the colonisation of California by the Spanish empire and the role of Serra and his Franciscan religious order in establishing modern California.
Imperfect Union: How Jessie and John Frémont Mapped the West, Invented Celebrity, and Helped Cause the Civil War by Steve Inskeep is my next recommendation. The book is about one of the most famous men of his time; so famous that he was compared to Jesus, Christopher Columbus and George Washington. His name was John Charles Fremont and his wife, the daughter of a US senator, became major celebrities in the 1850s. Think of them as the Kardashians of the times, albeit with accomplishments like mapping the road to the Pacific and leading the US army in its conquest of California during the Mexican-American war. The book covers the fascinating life stories of Fremont and his wife that led him to be the first Republican Presidential candidate, four years before Lincoln was elected.
Another book read is Andrew Jackson: His Life and Times by H.W. Brands. What could be more relevant these days than learning about Andrew Jackson, another controversial US figure, the President pictured on the $20 bill and who made a recent comeback in the public interest as part of the 2020 US presidential election. Much has been written about Jackson but this book by H.W. Brands is an easy-to-read, one-volume biography of a man widely considered to have been the most popular US president and who remains a polarizing figure almost two hundred years later.
Lastly, there is Blood Meridian: Or the Evening Redness in the Sky by Cormac McCarthy. This is a bonus for readers who prefer fiction and want to get a sense of life in the West in the 19th century. A masterpiece by Cormac McCarthy although not one for the faint-hearted.
800G MSA defines PSM8 while eyeing 400G’s progress
A key current issue regarding data centres is forecasting the uptake of 400-gigabit optics.
If a rapid uptake of 400-gigabit optics occurs, it will also benefit the transition to 800-gigabit modules. But if the uptake of 400-gigabit optics is slower, some hyperscalers could defer and wait for 800-gigabit pluggables instead.
So says Maxim Kuschnerov, a spokesperson for the 800G Pluggable MSA (multi-source agreement).
The 800G MSA has issued its first 800-gigabit pluggable specification.
Dubbed the PSM8, the design uses the same components as 400-gigabit optics, doubling capacity in the same QSFP-DD pluggable form factor.
“Four-hundred-gigabit modules hitting volume is crucially important because the 800-gigabit specification leverages 400-gigabit components,” says Kuschnerov. “The more 400-gigabit is delayed, it impacts everything that comes after.”
PSM8
The PSM8 is an eight-channel parallel single-mode (PSM) fibre design, each fibre carrying 100 gigabits of data.
The 100m-reach PSM8 version 1.0 specification was published in August, less than a year after the 800G MSA was announced.
The 800G Pluggable MSA is developing two other 800-gigabit specifications based on 200-gigabit electrical and optical lanes.
One is a 500m four-fibre 800-gigabit implementation, each fibre a 200-gigabit channel. This is an 800-gigabit equivalent of the existing 400-gigabit IEEE DR4 standard.
The second design is a single-fibre four-channel coarse wavelength-division multiplexing (CWDM) with a 2km reach, effectively an 800-gigabit CWDM4.
Specifications
The 800G MSA chose to tackle a parallel single-mode fibre design because the components needed already exist. In turn, a competing initiative, the IEEE’s 100-gigabit-per-lane multi-mode fibre approach, will have a lesser reach.
“The IEEE has an activity for 100-gigabit per lane for multi-mode but the reach is 50m,” says Kuschnerov. “How much market will you get with a limited-reach objective?”
In contrast, the 100m reach of the PSM8 better serves applications in the data centre and offers a path for single-mode fibre which, long-term, will provide general data centre connectivity, argues Kuschnerov, whether parallel fibre or a CWDM approach.
Investment will also be needed to advance multi-mode optics to achieve 100 gigabits whereas PSM8 will use 50 gigabaud optics already used by 400-gigabit modules.
Kuschnerov stresses that the PSM8 is not a repackaging of two IEEE 400-gigabit DR4s designs. The PSM8 uses more relaxed specifications to reduce cost; a possibility given PSM8’s 100m reach compared to the DR4’s 500m.
“We have relaxed various specifications to enable more choice,” says Kuschnerov. For example, externally modulated lasers (EMLs), directly modulated lasers (DMLs) and silicon photonics-based designs can all be used.
The transmitter power has also been reduced by 2.5dB compared to the DR4, while the extinction ratio of the modulator is 1.5dB less.
The need for an 800-gigabit in a QSFP-800DD form factor is to serve emerging 25.6-terabit Ethernet switches. Using 400-gigabit optics, a 2-rack-unit-high (2RU) switch is needed whereas a 1RU switch platform is possible using 800-gigabit pluggables.
“The big data centre players all have different plans and their own roadmaps,” says Kuschnerov. “From our observation of the industry, the upgrading speed for 400 gigabit and 800 gigabit is slower than what was expected a year ago.”
First samples of the PSM8 module are expected in the second half of 2021 with volume production in 2023.
800-gigabit PSM4 and CWDM4
The members of the MSA have already undertaking pre-development work on the two other specifications that use 200-gigabit-per-lane optics: the 800-gigabit PSM4 and the CWDM4.
“It was a lot of work discussing the feasibility of 200-gigabit-per-lane,” says Kuschnerov. There is much experimental work to be done regarding the choice of modulation format and forward error correction (FEC) scheme which will need to be incorporated in future 4-level pulse-amplitude modulation (PAM-4) digital signal processors.
“We are progressing, the key is low power and low latency which is crucial here,” says Kushnerov. A tradeoff will be needed in the chosen FEC scheme ensuring sufficient coding gain while minimising its contribution to the overall latency.
As for the modulation scheme, while different PAM schemes are possible, PAM-4 already looks like the front runner, says Kuschnerov.
The 800G Pluggable MSA is at the proof-of-concept stage, with a demonstration of working 200-gigabit-per-lane optics at the recent CIOE show held in Shenzhen, China. “Some of the components used are not just prototypes but are designed for this use case although we are not there yet with an end-to-end product.”
The designs will require 200-gigabit electrical and optical lanes. The OIF has just started work on 200-gigabit electrical interfaces and will likely only be completed in 2025. Achieving the required power consumption will also be a challenge.
Catalyst
Since the embrace of 200-gigabit-per-lane technology by the 800G Pluggable MSA just over a year ago, other initiatives are embracing the rate.
The IEEE has started its ‘Beyond 400G’ initiative that is defining the next Ethernet specification and both 800-gigabit and 1.6 terabit optics are under consideration. As has the OIF with its next-generation 224-gigabit electrical interface.
“These activities will enable a 200-gigabit ecosystem,” says Kuschnerov. “Our focus is on 800-gigabit but it is having a much wider impact beyond 4×200-gigabit, it is impacting 1.6 terabits and impacting serdes (serialisers/ deserialisers).”
The 800G Pluggable MSA is doing its small part but what is needed is the development of an end-to-end 200-gigabit ecosystem, he says: “This is a challenging undertaking.”
The 800G Pluggable MSA now has 40 members including hyperscalers, switch makers, systems vendors, and component and module makers.
Companies gear up to make 800 Gig modules a reality
Nine companies have established a multi-source agreement (MSA) to develop optical specifications for 800-gigabit pluggable modules.
The MSA has been created to address the continual demand for more networking capacity in the data centre, a need that is doubling roughly every two years. The largest switch chips deployed have a 12.8 terabit-per-second (Tbps) switching capacity while 25.6-terabit and 51-terabit chips are in development.
“The MSA members believe that for 25.6Tbps and 51.2Tbps switching silicon, 800-gigabit interconnects are required to deliver the required footprint and density,” says Maxim Kuschnerov, a spokesperson for the 800G Pluggable MSA.
A 1-rack-unit (1RU) 25.6-terabit switch platform will use 32, 800-gigabit modules while a 51.2-terabit 2RU platform will require 64.
The MSA has been founded now to ensure that there will be optical and electrical components for 800-gigabit modules...
Motivation
The founding members of the 800G MSA are Accelink, China Telecommunication Technology Labs, H3C, Hisense Broadband, Huawei Technology, Luxshare, Sumitomo Electric Industries, Tencent, and Yamaichi Electronics. Baidu, Inphi and Lumentum have since joined the MSA.
The MSA has been founded now to ensure that there will be optical and electrical components for 800-gigabit modules when 51.2-terabit platforms arrive in 2022.
And an 800-gigabit module will be needed rather than a dual 400-gigabit design since the latter will not be economical.
“Historically, the cost of optical short-reach interfaces has always scaled with laser count,” says Kuschnerov. “Pluggables with 8, 10 or 16 lasers have never been successful in the long run.”
He cites such examples as the first 100-gigabit module implemented using 10×10-gigabit channels, and the early wide-channel 400 Gigabit Ethernet designs such as the SR16 parallel fibre and the FR8 specifications. The yield for optics doesn’t scale in the same way as CMOS for parallel designs, he says.
That said, the MSA will investigate several designs for the different reaches. For 100m, 8-channel and 4-channel parallel fibre designs will be explored while for the longer reaches, single-fibre coarse wavelength division multiplexing (CWDM) technology will be used.
Shown from left to right are a PSM8 and a PSM4 module for 100m spans, and the CWDM4 design for 500m and 2km reaches. Source: 800G Pluggable MSA.
“Right now, we are discussing several technical options, so there’s no conclusion as to which design is best for which reach class,” says Kuschnerov.
The move to fewer channels is similar to how 400 Gigabit Ethernet modules have evolved: the 8-channel FR8 and LR8 module designs address early applications but, as demand ramp, they have made way for more economical four-channel FR4 and LR4 designs.
Specification work
The MSA will focus on several optical designs for the 800G Pluggable MSA, all using 112Gbps electrical input signals.
The first MSA design, for applications up to 100m, will explore 8×100-gigabit optical channels as a fast-to-market solution. This is a parallel single-mode 8-channel (PSM8) design, with each 100-gigabit channel carried over a dedicated fibre. The module will use 16 fibres overall: eight for input and eight for output. The MSA will also explore a PSM4 design – ‘the real 800G’ – where each fibre carries 200 gigabits.
The CWDM designs, for 500m and 2km, will require a digital signal processor (DSP) to implement four-level pulse-amplitude modulation (PAM4) signalling that generates the 200-gigabit channels. An optical multiplexer and demultiplexer will also be needed for the two designs.
The MSA will explore the best technologies for each of the three spans. The modulation technologies to be investigated include silicon photonics, directly modulated lasers (DML) and externally modulated lasers (EML).
Challenges
The MSA foresees several technical challenges at 800 gigabits.
One challenge is developing 100-gigabaud direct-detect optics needed to generate the four 200 gigabit channels using PAM4. Another is fitting the designs into a QSFP-DD or OSFP pluggable module while meeting their specified power consumption limitations. A third challenge is choosing a low-power forward error correction scheme and a PAM4 digital signal processor (DSP) that meet the MSA’s performance and latency requirements.
“We expect first conclusions in the fourth quarter of 2020 with the publication of the first specification,” says Kuschnerov.
The 800G Pluggable MSA is also following industry developments such as the IEEE proposal for the 8×100-gigabit SR8 over multi-mode fibre that uses VCSELs. But the MSA believes VCSELs represent a higher risk.
“Our biggest challenge is creating sufficient momentum for the 800-gigabit ecosystem, and getting key industry contributors involved in our activity,” says Kuschnerov.
Arista Networks, the switch vendor that has long promoted 800-gigabit modules, says it has no immediate plans to join the MSA.
“But as one of the supporters of the OSFP MSA, we are aligned in the need to develop an ecosystem of technology suppliers for components and test equipment for OSFP pluggable optics at 800 gigabits,” says Martin Hull, Arista’s associate vice president, systems engineering and platforms.
Hull points out that the OSFP pluggable module MSA was specified with 800 gigabits in mind.
Next-generation Ethernet
The fact that there is no 800 Gigabit Ethernet standard will not hamper the work, and the MSA cannot wait for the development of such a standard.
“The IEEE is in the bandwidth assessment stage for beyond 400-gigabit rates and we haven’t seen too many contributions,” says Kuschnerov. The IEEE would then need to start a Call For Interest and define an 800GbE Study Group to evaluate the technical feasibility of 800GbE. Only then will an 800GbE Task Force Phase start. “We don’t expect the work on 800GbE in IEEE to progress in line with our target for component sampling,” says Kuschnerov. First prototype 800G MSA modules are expected in the fourth quarter of 2021.
Arista’s Hull stresses that an 800GbE standard is not needed given that 800-gigabit modules support standardised rates based on 2×400-gigabit and 8×100-gigabit.
Moreover, speed increments for Ethernet are typically more than 2x. “That would suggest an expectation for 1 Terabit Ethernet (TbE) or 1.6TbE speeds,” says Hull. This was the case with the bandwidth transition from 10GbE to 40GbE (4x), and 40GbE to 100GbE (2.5x).
“It would be unusual for Ethernet’s evolution to slow to a 2x rate and make 800 Gigabit Ethernet the next step,” says Hull. “The introduction of 112Gbps serdes allows for a doubling of input-output (I/O) on a per-physical interface but this is not the next Ethernet speed.”
Pluggable versus co-packaged optics
There is an ongoing industry debate as to when switch vendors will be forced to transition from pluggable optics on the front panel to photonics co-packaged with the switch ASIC.
The issue is that with each doubling of switch chip speed, it becomes harder to get the data on and off the chip at a reasonable cost and power consumption. Driving the ever faster signals from the chip to the front-panel optics is also becoming challenging.
Packaging the optics with the switch chip enables the high-speed serialiser-deserialiser (serdes), the circuitry that gets data on and off the chip, to be simplified; no longer will the serdes need to drive high-speed signals across the printed circuit board (PCB) to the front panel. Adopting co-packaged optics simplifies the PCB design, constrains the switch chip’s overall power consumption given how hundreds of serdes are used, and reduces the die area reserved for the serdes.
But transitioning to co-packaged optics represents a significant industry shift.
The consensus at a panel discussion at the OFC show, held in March, entitled Beyond 400G for Hyperscaler Data Centres, was that the use of front-panel pluggable optics will continue for at least two more generations of switch chips: at 25.6Tbps and at 51.2Tbps.
It is a view shared by the 800G Pluggable MSA and one of its motivating goals.
“The MSA believes that 800-gigabit pluggables are technically feasible and offer clear benefits versus co-packaging,” says Kuschnerov. “As long as the industry can support pluggables, this will be the preferred choice of the data centre operators.”
It has always paid off to bet on the established technology as long as it is technically feasible due to the sheer amount of investment already made, says Kuschnerov.
Major shifts in interconnects such as coherent replacing direct detect, or PSM/ CWDM pushing out VCSELs, or optics replacing copper have happened only when legacy technologies approach their limits and which can’t be overcome easily, he says: “We don’t believe in such fundamental limitations for 800-gigabit pluggables.”
So when will the industry adopt co-packaged optics?
“We believe that beyond 51.2Tbps there is a very high risk surrounding the serdes and thus co-packaging might become necessary to overcome this limitation,” says Kuschnerov.
Switch-chip-maker, Broadcom, has said that co-packaged optics will be adopted alongside pluggables, enabling the hyperscalers to lessen the risk of the new technology’s introduction. Broadcom believes that co-packaged optics solutions will appear as early as the advent of 25.6-terabit switch chips.
An earlier transitional introduction is also a view shared by Hugo Saleh, vice president of marketing and business development at silicon photonics specialist at Ayar Labs, which recently unveiled its optical I/O chiplet technology is being co-packaged with Intel’s Stratix 10 FPGA.
Saleh says the consensus is that the node past 51.2Tbps must use in-packaged optics. But he also expects overlap before then, especially for high-end and custom solutions.
“It [co-packaged optics] is definitely coming, and it is coming sooner than some folks expect,” says Saleh.
Several companies have contacted the MSA since its 800-gigabit announcement. The 800G MSA is also in discussion with several component and module vendors that are about to join, from Asia and elsewhere. Inphi and Lumentum have joined since the MSA was announced.
Discussions have started with system vendors and hyperscale data center operators; Baidu is one that has since signed up.
Books in 2018 - Part 2
Some more books consumed in 2018, as recommended by Maxim Kuschnerov and Andrew Schmitt.
Maxim Kuschnerov, senior R&D manager at Huawei.
It is hard to believe the book Fire and Fury: Inside the Trump White House by Michael Wolff was published in 2018. Judging by what has happened since Trump’s inauguration, this recollection of his first days in the White House seems outdated. But it was fun to read while the memory of the election was still fresh. It is hard to judge whether all the book’s sources are truthful but the main message is certainly not too far off.
John Carreyrou’s Bad Blood: Secrets and Lies in a Silicon Valley Startup deals with the rise and fall of Elizabeth Holmes and her infamous blood testing start-up, Theranos. If it wasn’t for the fact that Holmes endangered the lives of thousands of people with her erroneous tests, one could be almost amazed on how she secured $1 billion from investors based on absolutely no technology whatsoever. It is also hard to believe how big chains could go along deploying Theranos tests without qualification of the products or the necessary Food and Drug Administration (FDA) approval.
As a westerner working for Huawei, Henry Kissinger’s On China was an important read to understand better how China sees itself and the world. There is no other nation capable of looking decades ahead like it is the fourth quarter of the next financial year. This is a worthwhile book for anyone wanting to make sense of the world.
Being a huge poker fan, buying the book Poker Brat: Phil Hellmuth’s Autobiography was a no-brainer. Hellmuth has his place in poker history, being one of the youngest World Series of Poker (WSOP) main event winners and the record holder with 15 bracelets. However, the book offers little insight on poker strategy. Or maybe it is the lack of strategy which makes Hellmuth who he is. If someone is really interested in learning from a great poker player, I’d recommend Every Hand Revealed by Gus Hansen. Hansen may have lost more than $20 million in online playing, but his book offers a better view on poker strategy back in the day of the big poker boom, before German maths wizards and game theory optimal strategy rewrote poker rules once again.
If a book has already been turned into a movie starring Brad Pitt, it means I am very late to the party with Michael Lewis’s Moneyball: The Art of Winning an Unfair Game. But being an artificial intelligence and machine-learning aficionado, everything is about recognising the underlying patterns, whether it is in images, optical signals or in such a beautiful and simple game like baseball. Most likely baseball strategists already apply machine learning to further optimise their strategy.
Andrew Schmitt, Founder and directing analyst at Cignal AI
The Winter Fortress: The Epic Mission to Sabotage Hitler's Atomic Bomb by Neal Bascomb is my pick of the year. I can’t believe this story isn't already a movie. It is about the Allies’ attempt to destroy the heavy-water plant in German-occupied Norway that was critical to the development of a German Atomic Weapon. Norwegians in exile in the UK, working with locals, pulled off a stunning attack that crippled the plant and set back the German effort. But the book is mostly about the events leading up to the mission, as well as the escape afterwards. The men who pulled it off were as hardcore as they come, and the sacrifices and impossible decisions they faced need to be shared. It is a story I imagine most Norwegians know, and it is a story that should be told to the world.
Hillbilly Elegy: A Memoir of a Family and Culture in Crisis by J.D. Vance is a good autobiography of someone who managed to escape people and situations that could easily have misdirected him. I am not going to join the chorus of folks who point to this book as reasoning for Trump getting elected; I avoid political discussions at all costs in a work environment. But reading this makes you appreciate the positive advantages you may have had growing up. The author, on the surface, had none but he highlights the people and situations that were formative for him and how they guided him on the right path. The best part about the book is that it isn’t preachy and Vance goes out of his way to explain that the problems he avoided have no easy or clear solutions.
Ray Dalio’s whitepapers, essays and explainer videos have always impressed me with concise formats and clear ideas. However, his book, Principles: Life and Work, is a big meal that I didn’t finish. I would recommend his YouTube videos and whitepapers and unless you are a hardcore self-help reader, which I’m not, then skip this.
My son had to read War by Sebastian Junger over the summer for High School. We read it together; a highly recommended thing to do with your teenagers. Junger was embedded in the Korengal Valley in Afghanistan with the US Army and was in the thick of some of the worst fighting. He also wrote The Perfect Storm which was a great book (and a terrible movie). In this book, he brings you right in the midst of events. If you want to know what being at the sharp end in Afghanistan is like, and the physical and mental sacrifices soldiers are making, then read this.
Michael Lewis is one of my favourite authors so I had to read his latest book, The Fifth Risk. It is well-written but it is about politics. I’m tired of politics. I don't think we need more of it so I won't recommend it.
I ripped through two volumes of Martha Wells’s The Murderbot Diaries on the way back from China. It’s about a security robot that figures out how to disable its governor software and become self-aware. A killing machine with a conscience, struggling with the details of being human. Some of the best Sci-Fi I’ve read in a long time. Netflix or Amazon need to give their money to this author right now and turn it into a series.
400ZR will signal coherent’s entry into the datacom world
- 400ZR will have a reach of 80km and a target power consumption of 15W
- The coherent interface will be available as a pluggable module that will link data centre switches across sites
- Huawei expects first modules to be available in the first half of 2020
- At OFC, Huawei announced its own 250km 400-gigabit single-wavelength coherent solution that is already being shipped to customers
Coherent optics will finally cross over into datacom with the advent of the 400ZR interface. So claims Maxim Kuschnerov, senior R&D manager at Huawei.
Maxim Kuschnerov400ZR is an interoperable 400-gigabit single-wavelength coherent interface being developed by the Optical Internetworking Forum (OIF).
The 400ZR will be available as a pluggable module and as on-board optics using the COBO specification. The IEEE is also considering a proposal to adopt the 400ZR specification, initially for the data-centre interconnect market. “Once coherent moves from the OIF to the IEEE, its impact in the marketplace will be multiplied,” says Kuschnerov.
But developing a 400ZR pluggable represents a significant challenge for the industry. “Such interoperable coherent 16-QAM modules won’t happen easily,” says Kuschnerov. “Just look at the efforts of the industry to have PAM-4 interoperability, it is a tremendous step up from on-off keying.”
Despite the challenges, 400ZR products are expected by the first half of 2020.
400ZR use cases
The web-scale players want to use the 400ZR coherent interface to link multiple smaller buildings, up to 80km apart, across a metropolitan area to create one large virtual data centre. This is a more practical solution than trying to find a large enough location that is affordable and can be fed sufficient power.
Once coherent moves from the OIF to the IEEE, its impact in the marketplace will be multiplied
Given how servers, switches and pluggables in the data centre are interoperable, the attraction of the 400ZR is obvious, says Kuschnerov: “It would be a major bottleneck if you didn't have [coherent interface] interoperability at this scale.”
Moreover, the advent of the 400ZR interface will signal the start of coherent in datacom. Higher-capacity interfaces are doubling every two years or so due to the webscale players, says Kuschnerov, and with the advent of 800-gigabit and 1.6-terabit interfaces, coherent will be used for ever-shorter distances, from 80km to 40km and even 10km.
At 10km, volumes will be an order of magnitude greater than similar-reach dense wavelength-division multiplexing (DWDM) interfaces for telecom. “Datacom is a totally different experience, and it won’t work if you don’t have a stable supply base,” he says. “We see the ZR as the first step combining coherent technology and the datacom mindset.”
Data centre players will plug 400ZR modules into their switch-router platforms, avoiding the need to interface the switch-router to a modular, scalable DWDM platform used to link data centres.
The 400ZR will also find use in telecom. One use case is backhauling residential traffic over a cable operator’s single spans that tend to be lossy. Here, ZR can be used at 200 gigabits - using 64 gigabaud signalling and QPSK modulation - to extend the reach over the high-loss spans. Similarly, the 400ZR can also be used for 5G mobile backhaul, aggregating multiple 25-gigabit streams.
Another application is for enterprise connectivity over distances greater than 10km. Here, the 400ZR will compete with direct-detect 40km ER4 interfaces.
Having several use cases, not just data-centre interconnect, is vital for the success of the 400ZR. “Extending ZR to access and metro-regional provides the required diversity needed to have more confidence in the business case,” says Kuschnerov.
The 400ZR will support 400 gigabits over a single wavelength with a reach of 80km, while the target power consumption is 15W.
The industry is still undecided as to which pluggable form factor to use for 400ZR. The two candidates are the QSFP-DD and the OSFP. The QSFP-DD provides backward compatibility with the QSFP+ and QSFP28, while the OSFP is a fresh design that is also larger. This simplifies the power management at the expense of module density; 32 OSFPs can fit on a 1-rack-unit faceplate compared to 36 QSFP-DD modules.
The choice of form factor reflects a broader industry debate concerning 400-gigabit interfaces. But 400ZR is a more challenging design than 400-gigabit client-side interfaces in terms of trying to cram optics and the coherent DSP within the two modules while meeting their power envelopes.
The OSFP is specified to support 15W while simulation results published at OFC 2018 suggest that the QSFP-DD will meet the 15W target. Meanwhile, the 15W power consumption will not be an issue for COBO on-board optics, given that the module sits on the line card and differs from pluggables in not being confined within a cage.
Kuschnerov says that even if it proves that only the OSFP of the two pluggables supports 400ZR, the interface will still be a success given that a pluggable module will exist that delivers the required face-plate density.
400G coherent
Huawei announced at OFC 2018 its own single-wavelength 400-gigabit coherent technology for use with its OptiX OSN 9800 optical and packet OTN platform, and it is already being supplied to customers.
The 400-gigabit design supports a variety of baud rates and modulation schemes. For a fixed-grid network, 34 gigabaud signalling enables 100 gigabits using QPSK, and 200 gigabits using 16-QAM, while at 45 gigabaud 200 gigabits using 8-QAM is possible. For flexible-grid networks, 64 gigabaud is used for 200-gigabit transmission using QPSK and 400 gigabits using 16-QAM.
Huawei uses an algorithm called channel-matched shaping to improve optical performance in terms of data transmission and reach. This algorithm includes such techniques as pre-emphasis, faster-than-Nyquist, and Nyquist shaping. According to Kuschnerov, the goal is to squeeze as much capacity out of a network’s physical channel so that advanced coding techniques such as probabilistic constellation shaping can be used to the full. For Huawei’s first 400-gigabit wavelength solution, constellation shaping is not used but this will be added in its upcoming coherent designs.
Huawei has already demonstrated the transmission of 400 gigabits over 250km of fibre. “Current generation 400G-per-lambdas does not enable long-haul or regional transmission so the focus is on shorter reach metro or data-centre-interconnect environments,” says Kuschnerov.
When longer reaches are needed, Huawei can offer two line cards, each supporting 200 gigabits, or a single line card hosting two 200-gigabit modules. The 200-gigabits-per-wavelength is achieved using 64 gigabaud and QPSK modulation, resulting in a 2,500km reach.
Up till now, such long-haul distances have been served using 100-gigabitwavelengths. Now, says Kuschnerov, 200 gigabit at 64 gigabaud is becoming the new norm in many newly built networks while the 34 gigabaud 200 gigabit is being favoured in existing networks based on a 50GHz grid.