Meeting the many needs of data centre interconnect
High capacity. Density. Power efficiency. Client-side optical interface choices. Coherent transmission. Direct detection. Open line system. Just some of the requirements vendors must offer to compete in the data centre interconnect market.
“A key lesson learned from all our interactions over the years is that there is no one-size-fits-all solution,” says Jörg-Peter Elbers, senior vice president of advanced technology, standards and IPR at ADVA Optical Networking. “What is important is that you have a portfolio to give customers what they need.”
Jörg-Peter Elbers
Teraflex
ADVA Optical Networking detailed its Teraflex, the latest addition to its CloudConnect family of data centre interconnect products, at the OFC show held in Los Angeles in March (see video).
The platform is designed to meet the demanding needs of the large-scale data centre operators that want high-capacity, compact platforms that are also power efficient.
A key lesson learned from all our interactions over the years is that there is no one-size-fits-all solution
Teraflex is a one-rack-unit (1RU) stackable chassis that supports three hot-pluggable 1.2-terabit modules or ‘sleds’. A sled supports two line-side wavelengths, each capable of coherent transmission at up to 600 gigabits-per-second (Gbps). Each sled’s front panel supports various client-side interface module options: 12 x 100-gigabit QSFPs, 3 x 400-gigabit QSFP-DDs and lower speed 10-gigabit and 40-gigabit modules using ADVA Optical Networking’s MicroMux technology.
“Building a product optimised only for 400-gigabit would not hit the market with the right feature set,” says Elbers. “We need to give customers the possibility to address all the different scenarios in one competitive platform.”
The Teraflex achieves 600Gbps wavelengths using a 64-gigabaud symbol rate and 64-ary quadrature-amplitude modulation (64-QAM). ADVA Optical Networking is using Acacia’s Communications latest Pico dual-core coherent digital signal processor (DSP) to implement the 600-gigabit wavelengths. ADVA Optical Networking would not confirm Acacia is its supplier but Acacia decided to detail the Pico DSP at OFC because it wanted to end speculation as to the source of the coherent DSP for the Teraflex. That said, ADVA Optical Networking points out that Teraflex’s modular nature means coherent DSPs from various suppliers can be used.
The 1 rack unit Teraflex
The line-side optics supports a variety of line speeds – from 600Gbps to 100Gbps, the lower the speed, the longer the reach.
The resulting 3-sled 1RU Teraflex platform thus supports up to 3.6 terabits-per-second (Tbps) of duplex communications. This compares to a maximum 800Gbps per rack unit using the current densest CloudConnect 0.5RU Quadflex card.
Markets
The data centre interconnect market is commonly split into metro and long haul.
The metro data centre interconnect market requires high-capacity, short-haul, point-to-point links up to 80km. Large-scale data centre operators may have several sites spread across a city, given they must pick locations where they can find them. Sites are typically no further apart than 80km to ensure a low-enough latency such that, collectively, they appear as one large logical data centre.
“You are extending the fabric inside the data centre across the data-centre boundary, which means the whole bandwidth you have on the fabric needs to be fed across the fibre link,” says Elbers. “If not, then there are bottlenecks and you are restricted in the flexibility you have.”
Large enterprises also use metro data centre interconnect. The enterprises’ businesses involve processing customer data - airline bookings, for example - and they cannot afford disruption. As a result, they may use twin data centres to ensure business continuity.
Here, too, latency is an issue especially if synchronous mirroring of data using Fibre Channel takes place between sites. The storage protocol requires acknowledgement between the end points such that the round-trip time over the fibre is critical. “The average distance of these connections is 40km, and no one wants to go beyond 80 or 100km,” says Elbers, who stresses that this is not an application for Teraflex given it is aimed at massive Ethernet transport. Customers using Fibre Channel typically need lower capacities and use more tailored solutions for the application.
The second data centre interconnect market - long haul - has different requirements. The links are long distance and the data sent between sites is limited to what is needed. Data centres are distributed to ensure continual business operation and for quality-of-experience by delivering services closer to customers.
Hundreds of gigabits and even terabits are sent over the long-distance links between data centres sites but commonly it is about a tenth of the data sent for metro data centre interconnect, says Elbers.
Direct Detection
Given the variety of customer requirements, ADVA Optical Networking is pursuing direct-detection line-side interfaces as well as coherent-based transmission.
At OFC, the system vendor detailed work with two proponents of line-side direct-detection technology - Inphi and Ranovus - as well as its coherent-based Teraflex announcement.
Working with Microsoft, Arista and Inphi, ADVA detailed a metro data centre interconnect demonstration that involved sending 4Tbps of data over an 80km link. The link comprised 40 Inphi ColorZ QSFP modules. A ColorZ module uses two wavelengths, each carrying 56Gbps using PAM-4 signalling. This is where having an open line system is important.
Microsoft wanted to use QSFPs directly in their switches rather than deploy additional transponders, says Elbers. But this still requires line amplification while the data centre operators want the same straightforward provisioning they expect with coherent technology. To this aim, ADVA demonstrated its SmartAmp technology that not only sets up the power levels of the wavelengths and provides optical amplification but also automatically measures and compensates for chromatic dispersion experienced over a link.
ADVA also detailed a 400Gbps metro transponder card based on PAM-4 implemented using two 200Gbps transmitter optical subassemblies (TOSAs) and two 200Gbps receiver optical subassemblies (ROSAs) from Ranovus.
Clearly there is also space for a direct-detection solution but that space will narrow down over time
Choices
The decision to use coherent or direct detection line-side optics boils down to a link’s requirements and the cost an end user is willing to pay, says Elbers.
As coherent-based optics has matured, it has migrated from long-haul to metro and now data centre interconnect. One way to cost-reduce coherent further is to cram more bits per transmission. “Teraflex is adding chunks of 1.2Tbps per sled which is great for people with very high capacities,” says Elbers, but small enterprises, for example, may only need a 100-gigabit link.
“For scenarios where you don’t need to have the highest spectral efficiency and the highest fibre capacity, you can get more cost-effective solutions,” says Elbers, explaining the system vendor’s interest in direct detection.
“We are seeing coherent penetrating more and more markets but still cost and power consumption are issues,” says Elbers. “Clearly there is also space for a direct-detection solution but that space will narrow down over time.”
Developments in silicon photonics that promise to reduce the cost of optics through greater integration and the adoption of packaging techniques from the CMOS industry will all help. “We are not there yet; this will require a couple of technology iterations,” says Elbers.
Until then, ADVA’s goal is for direct detection to cost half that of coherent.
“We want to have two technologies for the different areas; there needs to be a business justification [for using direct detection],” he says. “Having differentiated pricing between the two - coherent and direct detection - is clearly one element here.”
MultiPhy readies 100 Gigabit serial direct-detection chip
MultiPhy is developing a chip that will support serial 100 Gigabit-per-second (Gbps) transmission using 25 Gig optical components. The device will enable short reach links within the data centre and up to 80km point-to-point links for data centre interconnect. The fabless chip company expects to have first samples of the chip, dubbed FlexPhy, by year-end.
Figure 1: A block diagram of the 100 Gig serial FlexPhy. The transmitter output is an electrical signal that is fed to the optics. Equally, the input to the receive path is an electrical signal generated by the receiver optics. Source: Gazettabyte
The FlexPhy IC comprises multiplexing and demultiplexing functions as well as a receiver digital signal processor (DSP). The IC's transmitter path has a CAUI-4 (4x28 Gig) interface, a 4:1 multiplexer and four-level pulse amplitude modulation (PAM-4) that encodes two bits per symbol. The resulting chip output is a 50 Gbaud signal used to drive a laser to produce the 100 Gbps output stream.
"The input/output doesn't toggle at 100 Gig, it toggles at 50 Gig," says Neal Neslusan, vice president of sales and marketing at MultiPhy. "But 50 Gig PAM-4 is actually 100 Gigabit-per-second."
The IC's receiver portion will use digital signal processing to recover and decode the PAM-4 signals, and demultiplex the data into four 28 Gbps electrical streams. The FlexPhy IC will fit within a QSFP28 pluggable module.
As with MultiPhy's first-generation chipset, the optics are overdriven. With the MP1101Q 4x28 Gig multiplexer and MP1100Q four-channel receiver, 10 Gig optics are used to achieve four 28 Gig lanes, while with the FlexPhy, a 25 Gig laser is used. "Using a 25 GigaHertz laser and double-driving it to 50 GigaHertz induces some noise but the receiver DSP cleans it up," says Neslusan.
The use of PAM-4 incurs an optical signal-to-noise ratio (OSNR) penalty compared to non-return-to-zero (NRZ) signalling used for MultiPhy's first-generation direct-detection chipset. But PAM-4 has a greater spectral density; the 100 Gbps signal fits within a 50 GHz channel, resulting in 80 wavelengths in the C-band. This equates to 8 terabits of capacity to connect data centres up to 80 km apart.
Within the data centre, MultiPhy’s physical layer IC will enable 100 Gbps serial interfaces. The design could also enable 400 Gig links over distances of 500 m, 2 km and 10 km, by using four FlexPhys, four transmitter optical sub-assemblies (TOSAs) and four receiver optical sub-assemblies (ROSAs).
Meanwhile, MultiPhy's existing direct-detection chipset has been adopted by multiple customers. These include two optical module makers – Oplink and a Chinese vendor – and a major Chinese telecom system vendor that is using the chipset for a product coming to market now.
Ranovus readies its interfaces for deployment
- Products will be deployed in the first half of 2015
- Ranovus has raised US $24 million in a second funding round
- The start-up is a co-founder of the OpenOptics MSA; Oracle is now also an MSA member.
Ranovus says its interconnect products will be deployed in the first half of 2015. The start-up, which is developing WDM-based interfaces for use in and between data centres, has raised US $24 million in a second stage funding round. The company first raised $11 million in September 2013.
Saeid Aramideh"There is a lot of excitement around technologies being developed for the data centre," says Saeid Aramideh, a Ranovus co-founder and chief marketing and sales officer. He highlights such technologies as switch ICs, software-defined networking (SDN), and components that deliver cost savings and power-consumption reductions. "Definitely, there is a lot of money available if you have the right team and value proposition," says Aramideh. "Not just in Silicon Valley is there interest, but in Canada and the EU."
The optical start-up's core technology is a quantum dot multi-wavelength laser which it is combining with silicon photonics and electronics to create WDM-based optical engines. With the laser, a single gain block provides several channels while Ranovus is using a ring resonator implemented in silicon photonics for modulation. The company is also designing the electronics that accompanies the optics.
Aramideh says the use of silicon photonics is a key part of the design. "How do you enable cost-effective WDM?" he says."It is not possible without silicon photonics." The right cost points for key components such as the modulator can be achieved using the technology. "It would be ten times the cost if you didn't do it with silicon photonics," he says.
The firm has been working with several large internet content providers to turn its core technology into products. "We have partnered with leading data centre operators to make sure we develop the right products for what these folks are looking for," says Aramideh.
In the last year, the start-up has been developing variants of its laser technology - in terms of line width and output power - for the products it is planning. "A lot goes into getting a laser qualified," says Aramideh. The company has also opened a site in Nuremberg alongside its headquarters in Ottawa and its Silicon Valley office. The latest capital will be used to ready the company's technology for manufacturing and recruit more R&D staff, particularly at its Nuremberg site.
Ranovus is a founding member, along with Mellanox, of the 100 Gigabit OpenOptics multi-source agreement. Oracle, Vertilas and Ghiasi Quantum have since joined the MSA. The 4x25 Gig OpenOptics MSA has a reach of 2km-plus and will be implemented using a QSFP28 optical module. OpenOptics differs from the other mid-reach interfaces - the CWDM4, PSM4 and the CLR4 - in that it uses lasers at 1550nm and is dense wavelength-division multiplexed (DWDM) based.
It is never good that an industry is fragmented
That there are as many as four competing mid-reach optical module developments, is that not a concern? "It is never good that an industry is fragmented," says Aramideh. He also dismisses a concern that the other MSAs have established large optical module manufacturers as members whereas OpenOptics does not.
"We ran a module company [in the past - CoreOptics]; we have delivered module solutions to various OEMs that are running is some of the largest networks deployed today," says Aramideh. "Mellanox [the other MSA co-founder] is also a very capable solution provider."
Ranovus plans to use contract manufacturers in Asia Pacific to make its products, the same contract manufacturers the leading optical module makers use.
Table 1: The OpenOptics MSA
End markets
"I don't think as a business, anyone can ignore the big players upgrading data centres," says Aramideh. "The likes of Google, Facebook, Amazon, Apple and others that are switching from a three-tier architecture to a leaf and spine need longer-reach connectivity and much higher capacity." The capacity requirements are much beyond 10 Gig and 40 Gig, and even 100 Gig, he says.
Ranovus segments the adopters of interconnect into two: the mass market and the technology adopters. "Mass adoption today is all MSA-based," says Aramideh. "The -LR4 and -SR10, and the same thing is happening at 100 Gig with the QSFP28." The challenge for the optical module companies is who has the lowest cost.
Then there are the industry leaders such as the large internet content providers that want innovative products that address their needs now. "They are less concerned about multi-source standard-based solutions if you can show them you can deliver a product they need at the right cost," says Aramideh.
Ranovus will offer an optical engine as well as the QSFP28 optical module. "The notion of the integration of an optical engine with switch ICs and other piece parts in the data centre are more of an urgent need," he says.
Using WDM technology, the company has a scalable roadmap that includes 8x25 Gig and 16x25 Gig (400 Gig) designs. Also, by adding higher-order modulation, the technology will scale to 1.6 Terabit (16x100 Gig), says Aramideh.
I don't see a roadmap for coherent to become cost-effective to address the smaller distances
Ranovus is also working on interfaces to link data centres.
"These are distances much shorter than metro/ regional networks," says Aramideh, with the bulk of the requirements being for links of 15 to 40km. For such relatively short distances, coherent detection technology has a high-power consumption and is expensive. "I don't see a roadmap for coherent to become cost-effective to address the smaller distances," says Aramideh.
Instead, the company believes that a direct-detection interconnect that supports 15 to 40km and which has a spectral efficiency that can scale to 9.6 Terabit is the right way to go. If that can be achieved, then switching from coherent to direct detection becomes a no-brainer, he says. "For inter-data-centres, we are really offering an alternative to coherent."
The start-up says its technology will be in product deployment with lead customers in the first half of 2015.
MultiPhy eyeing 400 Gig after completing funding round
MultiPhy is developing a next-generation chip design to support 100 and 400 Gigabit direct-detection optical transmission. The start-up raised a new round of funding in 2013 but has neither disclosed the amount raised nor the backers except to say it includes venture capitalists and a 'strategic investor'.
The start-up is already selling its 100 Gig multiplexer and receiver chips to system vendors and module makers. The devices are being used for up to 80km point-to-point links and dense WDM metro/ regional networks spanning hundreds of kilometers. "In every engagement we have, the solutions are being sold in both data centre and telecom environments," says Avi Shabtai, CEO of MultiPhy.
The industry has settled on coherent technology for long-distance 100 Gig optical transmission but coherent is not necessarily a best fit for certain markets if such factors as power consumption, cost and compatibility with existing 10 Gig links are considered, says Shabtai.
The requirement to connect geographically-dispersed data centres has created a market for 100 Gig direct-detection technology. The types of data centre players include content service providers, financial institution such as banks, and large enterprises that may operate their own networks.
In every engagement we have, the solutions are being sold in both data centre and telecom environments
MultiPhy's two chips are the MP1101Q, a 4x25 Gig multiplexer device, and the MP1100Q four-channel receiver IC that includes a digital signal processor implementing the MLSE algorithm.
The chipset enables 10 Gig opto-electronics to be used to implement the 25 Gig transmitter and receiver channels. This results in a cost advantage compared to other 4x25 Gig designs. A design using the chipset can achieve 100 Gig transmissions over a 200GHz-wide channel or a more spectrally efficient 100GHz one. The latter achieves a transmission capacity of 4 Terabits over a fibre.
ADVA Optical Networking is one system vendor offering 100 Gig direct-detection technology while Finisar and Oplink Communications are making 100 Gigabit direct-detection optical modules. Oplink announced that it is using MultiPhy's chipset in 2013.
Overall, at least four system vendors are in advanced stages of developing 100 Gig direct-detection, and not all will necessarily announce their designs, says Shabtai. Whereas all the main optical transmission vendors have 100 Gig coherent technology, those backing 100 Gig direct detection may remain silent so as not to tip off their competitors, he says.
We assume we can do more using those [25 Gig] optical components with our technology
Meanwhile, the company is using the latest round of funding to develop its next-generation design. MultiPhy is focussed on high-speed direct-detection despite having coherent technology in-house. "Coherent is on our roadmap but direct detection is a very good opportunity over the next two years," says Shabtai. "You will see us come with solutions that also support 400 Gig."
A 400 Gigabit direct-detection design using its next generation chipset will likely come to market only in 2016 at the earliest by which time 25 Gig components will be more mature and cheaper. Using existing 25 Gig technology, a 400 Gig design requires 16, 25 Gig channels. However, the company will likely extend the performance of 25 Gig components to achieve even faster channel speeds, just like it does now with 10 Gig components to achieve 25 Gig speeds. The result will be a 400 Gig design with fewer than 16 channels. "We assume we can do more using those [25 Gig] optical components with our technology," says Shabtai.
Optical transport to grow at a 10% CAGR through 2017
- Global optical transport market to reach US $13bn in 2017
- 100 Gigabit to grow at a 75% CAGR
"I won't be surprised if it [100 Gig] grows even faster"
Jimmy Yu, Dell'Oro Group
The Dell'Oro Group forecasts that the global optical transport market will grow to US $13 billion in 2017, equating to a 10-percent compound annual growth rate (CAGR).
In 2012 SONET/SDH sales declined by over 20 percent, greater than Dell'Oro expected, while wavelength-division multiplexing (WDM) equipment sales held their own.
Regions
Dell'Oro expects optical transport growth across all the main regions, with no one region dominating. The market research company does foresee greater growth in Europe given the prolonged underspend of recent years.
European operators are planning broadband access investment such as fibre-to-the-cabinet/ VDSL vectoring as well as fibre-to-the-home. "That will drive demand for backhaul bandwidth and that is where WDM fits in well," says Jimmy Yu, vice president, microwave transmission, mobile backhaul and optical transport at Dell'Oro.
Technologies
Forty and 100 Gigabit optical transport will be the main WDM growth areas through 2017. Yu expects 40 Gigabit demand to grow over the forecast period even if the growth rate will taper off due to demand for 100 Gigabit.
The 100 Gigabit market continues to exceed Dell'Oro's forecasted growth. The market research company predicts 100-Gbps wavelength shipments to grow at a 75 percent CAGR over the next five years, accounting for 60 percent of the WDM capacity shipments by 2017. "I won't be surprised if it [100 Gig] grows even faster," says Yu.
"A lot of people wonder why have 40 Gig when there is 100 Gig? But that granularity does help service providers; having 40 Gig and 100 Gig rather than going straight from 10 Gig to 100 Gig," says Yu. The 100 Gig sales span metro and long-haul networks with the latter generating greater revenue due to the systems being pricier. "Forty Gigabit sales were predominantly long haul originally but we are seeing a good chunk of growth in metro as well," says Yu.
The current forecast does not include 400Gbps optical transport sales though Yu does expect sales to start in 2016.
Dell'Oro is seeing sales of 100 Gigabit direct detection but says it will remain a niche market. "We are talking tens of [shipped] units a quarter," says Yu.
There are applications where customers will need links of 80km or several hundred kilometers and will want the lowest cost solution, says Yu: "There is a market for direct detection; it will not be a significant driver for 100 Gig but it will be there."
Dan Sadot on coherent's role in the metro and the data centre
Gazettabyte went to visit Professor Dan Sadot, academic, entrepreneur and founder of chip start-up MultiPhy, to discuss his involvement in start-ups, his research interests and why he believes coherent technology will not only play an important role in the metro but also the data centre.
"Moore's Law is probably the most dangerous enemy of optics"
Professor Dan Sadot
The Ben-Gurion University campus in Beer-Sheba, Israel, is a mixture of brightly lit, sharp-edged glass-fronted buildings and decades-old Palm trees.
The first thing you notice on entering Dan Sadot's office is its tidiness; a paperless desk on which sits a MacBook Air. "For reading maybe the iPad could be better but I prefer a single device on which I can do everything," says Sadot, hinting at a need to be organised, unsurprising given his dual role as CTO of MultiPhy and chairman of Ben-Gurion University's Electrical and Computer Engineering Department.
The department, ranked in the country's top three, is multi-disciplinary. Just within the Electrical and Electronics Department there are eight tracks including signal processing, traditional communications and electro-optics. "That [system-oriented nature] is what gives you a clear advantage compared to experts in just optics," he says.
The same applies to optical companies: there are companies specialising in optics and ASIC companies that are expert in algorithms, but few have both. "Those that do are the giants: [Alcatel-Lucent's] Bell Labs, Nortel, Ciena," says Sadot. "But their business models don't necessarily fit that of start-ups so there is an opportunity here."
MultiPhy
MultiPhy is a fabless start-up that specialises in high-speed digital signal processing-based chips for optical transmission. In particular it is developing 100Gbps ICs for direct detection and coherent.
Sadot cites a rule of thumb that he adheres to religiously: "Everything you can do electronically, do not do optically. And vice versa: do optically only the things you can't do electronically." This is because using optics turns out to be more expensive.
And it is this that MultiPhy wants to exploit by being an ASIC-only company with specialist knowledge of the algorithms required for optical transmission.
"Electronics is catching up," says Sadot. "Moore's Law is probably the most dangerous enemy of optics."
Ben-Gurion University Source: Gazettabyte
Direct detection
Not only have developments in electronics made coherent transmission possible but also advances in hardware. For coherent, accurate retrieval of phase information is needed and that was not possible with available hardware until recently. In particular the phase noise of lasers was too high, says Sadot. Now optics is enabling coherent, and the issues that arise with coherent transmission can be solved electronically using DSP.
MultiPhy has entered the market with its MP1100Q chip for 100Gbps direct detection. According to Sadot, 100Gbps is the boundary data rate between direct detection and coherent. Below 100Gbps coherent is not really needed, he says, even though some operators are using the technology for superior long-haul optical transmission performance at 40Gbps.
"Beyond 100 Gig you need the spectral efficiency, you need to do denser [data] constellations so you must have coherent," says Sadot. "You are also much more vulnerable to distortions such as chromatic dispersion and you must have the coherent capability to do that."
But at 100 Gig the two - coherent and direct detection - will co-exist.
MultiPhy's first device runs the maximum likelihood sequence estimation (MLSE) algorithm that is used to counter fibre transmission distortions. "MLSE offers the best possible theoretical solution on a statistical basis without retrieving the exact phase," says Sadot. "That is the maximum you can squeeze out of direct detection."
The MLSE algorithm benefits optical performance by extending the link's reach while allowing lower cost, reduced-bandwidth optical components to be used. MultiPhy claims 4x10Gbps can be used for the transmit and the receive path to implement the 4x28Gbps (100Gbps) design.
Sadot describes MLSE as a safety net in its ability to handle transmitter and/or receiver imperfections. "We have shown that performance is almost identical with a high quality transmitter and a lower quality transmitter; MLSE is an important addition." he says.
Ben-Gurion University Source: Gazettabyte
Coherent metro
System vendors such as Ciena and Alcatel-Lucent have recently announced their latest generation coherent ASICs designed to deliver long-haul transmission performance. But this, argues Sadot, is overkill for most applications when ultra-long haul is not needed: metro alone accounts for 75% of all the line side ports.
He also says that the power consumption of long-haul solutions is over 3x what is required for metro: 75W versus the CFP pluggable module's 24W. This means the power available solely for the ASIC would be 15W.
"This is not fine-tuning; you really need to design the [coherent metro ASIC] from scratch," says Sadot. "This is what we are doing."
To achieve this, MultiPhy has developed patents that involve “sub-Nyquist” sampling. This allows the analogue-to-digital converters and the DSP to operate at half the sampling rate, saving power. To use sub-Nyquist sampling, a low-pass anti-aliasing filter is applied but this harms the received signal. Using the filter, sampling at half the rate can occur and using the MLSE algorithm, the effects of the low-pass filtering can be countered. And because of the low pass filtering, reduced bandwidth opto-electronics can be used which reduces cost.
The result is a low power, cost-conscious design suited for metro networks.
Coherent elsewhere
Next-generation PON is also a likely user of coherent technology for such schemes as ultra-dense WDM-PON.
Sadot believes coherent will also find its way into the data centre. "Again you will have to optimise the technology to fit the environment - you will not find an over-design here," he says.
Why would coherent, a technology associated with metro and long-haul, be needed in the data centre?
"Even though there is the 10x10 MSA, eventually you will be limited by spectral efficiency," he says. Although there is a tremendous amount of fibre in the data centre, there will be a need to use this resource to the maximum. "Here it will be all about spectral efficiency, not reach and optical signal-to-noise," says Sadot.
Sadot's start-ups
Sadot had a research posting at the optical communications lab at Stanford University. The inter-disciplinary and systems-oriented nature of the lab was an influence on Sadot when he founded the optical communications lab at Ben-Gurion University around the time of the optical boom. "A pleasant time to come up with ideas," is how he describes that period - 1999-2000.
The lab's research focus is split between optical and signal processing topics. Work there resulted in two start-ups during the optical bubble which Sadot was involved in: Xlight Photonics and TeraCross.
Xlight focused on ultra-fast lasers as part of a tunable transponder. Xlight eventually merged with another Israeli start-up Civcom, which in turn was acquired by Padtek.
The second start-up, TeraCross, looked at scheduling issues to improve throughput in Terabit routers. "The start-up led to a reference design that was plugged into routers in Cisco's Labs in Santa Clara [California]," says Sadot. "It was the first time a scheduler showed the capability to support a one Terabit data stream, and route in a sophisticated, global manner."
But with the downturn of the market, the need for terabit routers disappeared and the company folded.
Sadot's third and latest start-up, MultiPhy, also has its origins in Ben-Gurion's optical communications lab's work on enabling system upgrades without adding to system cost.
MultiPhy started as a PON company looking at how to upgrade GPON and EPON to 10 Gigabit PON without changing the hardware. "The magic was to use previous-generation hardware which introduces distortion as it doesn't really fit this upgrade speed, and then to compensate by signal processing," says Sadot.
After several rounds of venture funding the company shifted its focus from PON, applying the concept to 100 Gigabit optical transmission instead.
100 Gigabit direct detection gains wider backing
More vendors are coming to market with 100 Gigabit direct detection products for metro and private networks.
The emergence of a second de-facto 100 Gigabit standard, a complement to 100 Gigabit coherent, has gained credence with 4x28 Gigabit-per-second (Gbps) direct detection announcements from Finisar and Oclaro, as well as backing from system vendor, ECI Telecom.
"We believe that in some cases operators will prefer to go with this technology instead of coherent"
Shai Stein, CTO, ECI Telecom
ECI Telecom and chip vendor MultiPhy announced at OFC/NFOEC that they have been collaborating to develop a 168-pin MSA, 5x7-inch 100 Gigabit-per-second (Gbps) direct detection module. Finisar and Oclaro used the show held in Los Angeles to announce their market entry with 100Gbps direct detection CFP pluggable optical modules.
Late last year ADVA Optical Networking announced the industry's first 100Gbps direct detection product. At the same time, MultiPhy detailed its MP1100Q receiver chip designed for 100Gbps direct detection.
According to ECI, by having the 168-pin MSA interface, one line card can support a 100Gbps coherent transponder or the 100Gbps direct detection. "This is important as it enables us to fit the technology and price to the needs of end customers," says Shai Stern, CTO of ECI Telecom.
100 Gigabit transmission
Coherent technology has become the de-facto standard for 100Gbps long-haul transmission. Using dense wavelength division multiplexing (DWDM), system vendors can achieve 1,500km and greater reaches using a 50GHz channel.
But coherent designs are relatively costly and 100Gbps direct detection offers a cost-conscious alternative for metro networks and for linking data centres, achieving a reach of up to 800km.
"It [100 Gig direct detection] provides needed performance at an attractive cost, in particular when you are looking at private optical networks," says Per Hansen, vice president of product marketing, optical networks solutions at Oclaro.
Such networks need not be owned by private enterprises, they can belong to operators, says Hansen, but they are typically simple point-to-point connections or 3- to 4-node rings serving enterprises. "Bonding adjacent [4x28Gbps] wavelengths to create a 100Gbps channel that connects efficiently to your [IP] router is very attractive in such networks," says Hansen.
For more complex mesh metro networks, coherent is more attractive. "Simply because of the spectral resources being taken up through the mesh [with 4x28Gbps], and the operational aspect of routeing that," says Hansen.
ECI Telecom says that it has yet to decide whether it will adopt 100Gbps direct detection. But it does see a role for the technology in the metro since the 100Gbps technology works well alongside networks with 10 and 40 Gigabit on-off keying (OOK) channels. "We believe that in some cases operators will prefer to go with this technology instead of coherent," says Stein.
Some operators have chosen to deploy coherent over new overlay networks, to avoid the non-linear transmission effects that result from mixing old and new technologies on the one network. "With this technology, operators can stay with their existing networks yet benefit from 100 Gig high capacity links," says Stein.
Finisar says 100Gbps direct detection is also suited to low-latency applications. "The fact that it is not coherent means it doesn't include a DSP chip, enabling it to be used for low latency applications," says Rafik Ward, vice president of marketing at Finisar.
Implementation
The announced 100Gbps direct detection designs all use 4x28Gbps channels and optical duo-binary (ODB) modulation, although MultiPhy also promotes an 80km point-to-point OOK version (see Table).
Source: Gazettabyte
The module input is a 10x10Gbps electrical interface: a CFP interface or the 168-pin line side MSA. A 'gearbox' IC is used to translate between the 10x10Gbps electrical interface and the four 28Gbps channels feeding the optics.
"There are a few suppliers that are offering that [gearbox IC]," says Robert Blum, director of product marketing for Oclaro's photonic components. AppliedMicro recently announced a duplex multiplexer-demultiplexer IC.
MultiPhy's receiver chip has a digital signal processor (DSP) that implements the maximum likelihood sequence estimation (MLSE) algorithm, which is says enables 10 Gig opto-electronics to be used for each channel. The result is a 100Gbps module based on the cost of 4x10Gbps optics. However, over-driving the 10Gbps opto-electronics creates inter-symbol interference, where the energy of a transmitted bit leaks into neighbouring signals. MultiPhy's DSP using MLSE counters the inter-symbol interference.
100G direct detection module showing MultiPhy's MP1100Q chip. Source: MultiPhy
Oclaro and Finisar claim that using ODB alone enables the use of lower-speed opto-electronics. "This is irrespective of whether you use MLSE or hard decision," says Blum. "The advantage of using optical duo-binary modulation is that you can use 10G-type optics."
Finisar's Ward points out that by using ODB, the 100Gbps direct-detection module avoids the price/ power penalty associated with a receiver DSP running MLSE to compensate for sub-optimal optical components.
Oclaro, however, has not ruled out using MLSE in future. The company endorsed MultiPhy's MLSE device when the product was first announced but its first 100G transceiver is not using the IC.
Finisar and Oclaro's modules require 200GHz to transmit the 100Gbps signal: 4x50GHz channels, each carrying the 28Gbps signal. "This architecture will enable 2.5x the spectral efficiency of tunable XFPs," says Ward. Using XFPs, ten would be needed for a 100Gbps throughput, each channel requiring 50GHz or 500GHz in total.
MultiPhy claims that it can implement the 100Gbps in a 100GHz channel, 5x the efficiency but still twice the spectrum used for 100Gbps coherent.
Finisar demonstrated its 100Gbps CFP module with SpectraWave, a 1 rack unit (1U) DWDM transport chassis, at OFC/NFOEC. "It provides all the things you need in line to enable a metro Ethernet link: an optical multiplexer and demultiplexer, amplification and dispersion compensation," says Ward. Up to four CFPs can be plugged into the SpectraWave unit.
Operator interest
In a recent survey published by Infonetics Research, operators had yet to show interest in 100Gbps direct detection. Infonetics attributed the finding to the technology still being unavailable and that operators hadn't yet assessed its merits.
"Operators are aware of this technology," says ECI's Stein. "It is true they are waiting to get a proof-of-concept and to test it in their networks and see the value they can get.
"That is why ECI has not yet decided to go for a generally-available product: we will deliver to potential customers, get their feedback and then take a decision regarding a commercial product," says Stein.
However MultiPhy claims that this is the first technology that enables 100Gbps in a pluggable module to achieve a reach beyond 40km. That fact coupled with the technology's unmatched cost-performance is what is getting the interest. "Every time you show a potential user some way they can save on cost, they are interested," says Neal Neslusan, vice president of sales and marketing at MultiPhy.
Direct detection roadmap
Recent announcements by Cisco Systems, Ciena, Alcatel-Lucent and Huawei highlight how the system vendors will use advanced modulation and super-channels to evolve coherent to speeds beyond 100Gbps. Does direct detection have a similar roadmap?
"I don't think that this on-off keying technology is coming instead of coherent," says Stein. "Once we move to super-channel and the spectral densities it can achieve, coherent technology is a must and will be used." But for 40Gbps and 100Gbps, what ECI calls intermediate rates, direct detection extends the life of OOK and existing network infrastructure.
ECI and MultiPhy are members of the Tera Santa Consortium developing 1 Terabit coherent technology, and MultiPhy stresses that as well as its direct detection DSP chips, it is also developing coherent ICs.
Further reading: 100 Gigabit: The coming metro opportunity
100 Gigabit: The Coming Metro Opportunity
Gazettabyte has published a Position Paper on the coming 100 Gigabit metro opportunity. (Click here to download a copy.) There has been several announcements in recent weeks from system and component vendors addressing 100 Gigabit metro networks.
The 19-page report looks at the status of the 100 Gigabit market, the drivers for 100 Gigabit deployment, the technology options and their merits. The paper then states how 100 Gigabit technologies such as direct-detection point-to-point, direct-detection WDM and coherent will fare in the metro.
Gazettabyte interviewed over 20 operators, system vendors, optical module and component makers for the Position Paper.
These include ADVA Optical Networks, Alcatel-Lucent, Brocade, BT, BTI Systems, Ciena, Cisco Systems, Cyoptics, John D'Ambrosia - chair of IEEE 100 Gig backplane study group, ECI Telecom, Ericsson, Finisar, Huawei, Infinera, Ixia, Juniper Networks, MultiPhy, Nokia Siemens Networks, Oclaro, Opnext, Level 3 Communications, Transmode, Verizon and ZTE.
Look forward to any comments you may have regarding the report, its position and conclusions.
Transmode chooses coherent for 100 Gigabit metro
Transmode has detailed its 100 Gigabit metro strategy based on a stackable rack, a concept borrowed from the datacom world.
The Swedish system vendor has adopted coherent detection technology for 100 Gigabit-per-second (Gbps) optical transmission, unlike other recent metro announcements from ADVA Optical Networking and MultiPhy based on 100Gbps direct-detection.
"Metro is a little bit diverse. You see different requirements that you have to adapt to."
Sten Nordell, Transmode
"We are getting requests for this and we think 2012 is when people are going to put in a low number of [100Gbps] links into the metro," says Sten Nordell, CTO at Transmode.
The 100Gbps requirements Transmode is seeing include connecting data centres over various distances. The data centres can be close - tens of kilometers - or hundreds of kilometers apart.
"They [data centre operators] want to get more capacity over longer distances over the fibre they have rented," says Nordell. "That is why we are going down the standards path of coherent technology that gives you that boost in power and distance."
Nordell says that customers typically only want one or two 100Gbps light paths to expand fibre capacity or to connect IP routers over a link already carrying multiple 10Gbps light paths. "Metro is a little bit diverse," he says. "You see different requirements that you have to adapt to."
Rack system approach
Transmode has adopted a stackable approach to its 100Gbps TM-series of chassis. The TM-2000 is a 4U-high dual 100Gbps rack that implements transponder, muxponder or regeneration functions. "We have borrowed from Ethernet switches - you add as you grow," says Nordell.
Up to four TM-2000 are used with one TM-301 or TM-3000 master rack, with the architecture supporting up to 80, 100Gbps wavelengths overall.
"If you have too many ROADMs in the way it is going to hurt you. We have seen that with 40 Gig."
The system also uses daughter boards that support various client-side interfaces while keeping the 100Gbps line-side interface - the most expensive system component - intact. "You can install a muxponder of 10x10Gig modules,” says Nordell. "When an IP router upgrades to a 100 Gig interface, you take out the daughter board and put in a 100 Gig transponder."
Transmode will offer two line-side coherent options, with a reach of 750km or 1,500km. "We want to make sure that customers' metro and long-haul requirements will be covered," says Nordell.
The reach of various 100Gbps technologies for the metro edge, core and regional networks. Source: Gazettabyte
The company chose coherent technology because it is an industry-backed standard. "We can benefit from coherent technology," he says. "If the industry aligns, the volumes of the components come down in price."
Coherent also simplifies the setting up and commissioning of agile photonic networks, especially as more ROADMs are introduced in the metro. "Coherent will help simplify this. All the others are more complex," he says. "Beforehand metro was more point-to-point, now we are seeing more flexibility."
Transmode recently announced it is supplying its systems to Virgin Mobile for mobile backhaul. "That is a metro network with all ROADMs in it," says Nordell. Such networks support multiple paths and that translates to a need for greater reach. "The power budget we need to have in the metro is going up a little bit."
Direct-detection technology was considered by Transmode but it chose coherent as it gives customers a better networking design capability.
Direct detection is also not as spectrally efficient as coherent: 200GHz or 100GHz-wide channels for a 100Gbps signal rather that coherent's 50GHz. "If you have too many ROADMs in the way it is going to hurt you, says Nordell.”We have seen that with 40 Gig."
The TM-2000 rack will begin testing in customers' networks at the start of 2012, with limited availability from mid-2012. The platform and daughter boards will be available in volume by year-end 2012.
MultiPhy boosts 100 Gig direct-detection using digital signal processing
The MP1100Q chip is being aimed at two cost-conscious metro networking requirements: 100 Gigabit point-to-point links and dense wavelength-division multiplexing (DWDM) metro networks.
The MP1100Q as part of a 100 Gig CFP module design. Source: MultiPhy
The 100 Gigabit market is still in its infancy and the technology has so far been used to carry traffic across operators’ core networks. Now 100 Gigabit metro applications are emerging.
Data centre operators want short links that go beyond the IEEE-specified 10km (100GBASE-LR4) and 40km (100GBASE-ER4) reach interfaces, while enterprises are looking to 100 Gigabit-per-second (Gbps) DWDM solutions to boost the capacity and reach of their rented fibre. Existing 100Gbps coherent technologies, designed for long-haul, are too expensive and bulky for the metro.
“There is long-haul and the [IEEE] client interfaces and a huge gap in between,” says Avishay Mor, vice president of product management at MultiPhy.
It is this metro 'gap' that MultiPhy is targeting with its MQ1100Q chip. And the fabless chip company's announcement is one of several that have been made in recent weeks.
ADVA Optical Networking has launched a 100Gbps metro line card that uses a direct-detection CFP, while Transmode has detailed a 100Gbps coherent design tailored for the metro. The 10x10 MSA announced in August a 10km interface as well as a 40km WDM design alongside its existing 10x10Gbps MSA that has a 2km reach.
MultiPhy's MP1100Q IC will enable two CFP module designs: a point-to-point module to connect data centres with a reach of up to 80km, and a DWDM design for metro core and regional networks with a reach up to 800km.
"MLSE is recognised as the best solution for mitigating inter-symbol interference."
Design details
The M1100Q uses a 4x28Gbps direct-detection design, the same approach announced by ADVA Optical Networking for its 100Gbps metro card. But MultiPhy claims that the 100Gbps DWDM CFP module will squeeze the four bands that make up the 100Gbps signal into a 100GHz-wide channel rather than 200GHz, while its IC implements the maximum likelihood sequence estimation (MLSE) algorithm to achieve the 800km reach.
The four optical channels received by a CFP are converted to electrical signals using four receiver optical subassemblies (ROSAs) and sampled using the MP1100Q’s four analogue-to-digital (a/d) converters operating at 28Gbps.
The CFP design using MultiPhy’s chip need only use 10Gbps opto-electronics for the transmit and receive paths. The result is a 100Gbps module with a cost structure based on 4x10Gbps optics.
The lower bill-of-materials impacts performance, however. “When you over-drive these 10Gbps opto-electronics - on the transmit and the receive side - you create what is called inter-symbol interference," says Neal Neslusan, vice president of sales and marketing at MultiPhy.
Inter-symbol interference is an unwanted effect where the energy of a transmitted bit leaks into neighboring signals. This increases the bit-error rate and makes the detector's task harder. "The way that we get around it is using MLSE, recognised as the best solution for mitigating inter-symbol interference," says Neslusan.
Unwanted channel effects introduced by the fibre, like chromatic dispersion, also induce inter-symbol interference and are also countered by the MLSE algorithm on the MP1100Q.
MultiPhy is proposing two CFP designs for its chip. One is based on on-off-keying modulation to achieve 80km point-to-point links and which will require a 200GHz channel to accommodate the 100Gbps signal. The second uses optical duo-binary modulation to achieve the longer reach and more spectrally efficient 100GHz spacings.
The company says the resulting direct-detection CFP using its IC will cost some US $10,000 compared to an estimated $50,000 for a coherent design. In turn the 100G metro CFP’s power consumption is estimated at 24W whereas a coherent design consumes 70W.
MP1100Q samples have been with the company since June, says Mor. First samples will be with customers in the fourth quarter of this year, with general availability starting in early 2012.
If all goes to plan, first CFP module designs using the chip will appear in the second half of 2012, claims MultiPhy.