Latest coherent ASICs set the bar for the optical industry
Feature: Beyond 100G - Part 3
Alcatel-Lucent has detailed its next-generation coherent ASIC that supports multiple modulation schemes and allow signals to scale to 400 Gigabit-per-second (Gbps).
The announcement follows Ciena's WaveLogic 3 coherent chipset that also trades capacity and reach by changing the modulation scheme.
"They [Ciena and Alcatel-Lucent] have set the bar for the rest of the industry," says Ron Kline, principal analyst for Ovum’s network infrastructure group.
"We will employ [the PSE] for all new solutions on 100 Gigabit"
Kevin Drury, Alcatel-Lucent
Photonic service engine
Dubbed the photonic service engine (PSE), Alcatel-Lucent's latest ASIC will be used in 100Gbps line cards that will come to market in the second half of 2012.
The PSE compromises coherent transmitter and receiver digital signal processors (DSPs) as well as soft-decision forward error correction (SD-FEC). The transmit DSP generates the various modulation schemes, and can perform waveform shaping to improve spectral efficiency. The coherent receiver DSP is used to compensate for fibre distortions and for signal recover.
The PSE follows Alcatel-Lucent's extended reach (XR) line card announced in December 2011 that extends its 100Gbps reach from 1,500 to 2,000km. "This [PSE] will be the chipset we will employ for all new solutions on 100 Gigabit," says Kevin Drury, director of optical marketing at Alcatel-Lucent. The PSE will extend 100Gbps reach to over 3,000km.
Ciena's WaveLogic 3 is a two-device chipset. Alcatel-Lucent has crammed the functionality onto a single device. But while the device is referred to as the 400 Gigabit PSE, two PSE ASICs are needed to implement a 400Gbps signal.
"They [Ciena and Alcatel-Lucent] have set the bar for the rest of the industry"
Ron Kline, Ovum
"There are customers that are curious and interested in trialling 400Gbps but we see equal, if not higher, importance in pushing 100Gbps limits," says Manish Gulyani, vice president, product marketing for Alcatel-Lucent's networks group.
In particular, the equipment maker has improved 100Gbps system density with a card that requires two slots instead of three, and extends reach by 1.5x using the PSE.
Performance
Alcatel-Lucent makes several claims about the performance enhancements using the PSE:
- Reach: The reach is extended by 1.5x.
- Line card density: At 100Gbps the improvement is 1.5x. The current 100Gbps muxponder (10x10Gbps client input) and transponder (100Gbps client) line card designs occupy three slots whereas the PSE design will occupy two slots only. Density will be improved by 4x by adopting a 400Gbps muxponder that occupies three slots.
- Power consumption: By going to a more advanced CMOS process and by enhancing the design of the chip architecture, the PSE consumes a third less power per Gigabit of transport: from 650mW/Gbps to 425mW/Gbps. Alcatel-Lucent is not saying what CMOS process technology is used for the PSE. The company's current 100Gbps silicon uses a 65nm process and analysts believe the PSE uses a 40nm process.
- System capacity: The channel width occupied by the signal can be reduced by a third. A 50GHz 100Gbps wavelength can be compressed to occupy a 37.5GHz. This would improve overall 100Gbps system capacity from 8.8 Terabit-per-second (Tbps) to 11.7Tbps. Overall capacity can be improved from 88, 100Gbps ports to 44, 400Gbps interfaces. That doubles system capacity to 17.6Tbps. Using waveform shaping, this is improved by a further third, to greater than 23Tbps.
"We are not saying we are breaking the 50GHz channel spacing today and going to a flexible grid, super-channel-type construct," says Drury. "But this chip is capable of doing just that." Alcatel-Lucent will at least double network capacity when its system adopts 44 wavelengths, each at 400Gbps.
400 Gigabit
To implement a 400Gbps signal, a dual-carrier, dual-polarisation 16-QAM coherent wavelength is used that occupies 100GHz (two 50GHz channels). Alcatel-Lucent says that should it commercialise 400Gbps using waveform shaping, the channel spacing would reduce to 75GHz. But this more efficient grid spacing only works alongside a flexible grid colourless, directionless and contentionless (CDC) ROADM architecture.
A 400Gbps PSE card showing four 100 Gigabit Ethernet client signals going out as a 400Gbps wavelength. The three-slot card is comprised of three daughter boards. Source: Alcatel-Lucent.
Alcatel-Lucent is not ready to disclose the reach performance it can achieve with the PSE using the various modulation schemes. But it does say the PSE supports dual-polarisation bipolar phase-shift keying (DP-BPSK) for longest reach spans, as well as quadrature phase-shift keying (DP-QPSK) and 16-QAM (quadrature amplitude modulation).
"[This ability] to go distances or to sacrifice reach to increase bandwidth, to go from 400km metro to trans-Pacific by tuning software, that is a big advantage," says Ovum's Kline. "You don't then need as many line cards and that reduces inventory."
Market status
Alcatel-Lucent says that it has 55 customers that have deployed over 1,450 100Gbps transponders.
A software release later this year for Alcatel-Lucent's 1830 Photonic Service Switch will enable the platform to support 100Gbps PSE cards.
A 400Gbps card will also be available this year for operators to trial.
Cisco Systems' 100 Gigabit spans metro to ultra long-haul
Cisco Systems has demonstrated 100 Gigabit transmission over a 3,000km span. The coherent-based system uses a single carrier in a 50GHz channel to transmit at 100 Gigabit-per-second (Gbps). According to Cisco, no Raman amplification or signal regeneration is needed to achieve the 3,000km reach.
Feature: Beyond 100G - Part 2
"The days of a single modulation scheme on a part are probably going to come to an end in the next two to three years"
Greg Nehib, Cisco
The 100Gbps design is also suited to metro networks. Cisco's design is compact to meet the more stringent price and power requirements of metro. The company says it can fit 42, 100Gbps transponders in its ONS 15454 Multi-service Transport Platform (MSTP), which is a 7-foot rack. "We think that is double the density of our nearest competitor today," claims Greg Nehib, product manager, marketing at Cisco Systems.
Also shown as part of the Cisco demonstration was the use of super-channels, multiple carriers that are combined to achieve 400 Gigabit or 1 Terabit signals.
Single-carrier 100 Gigabit
Several of the first-generation 100Gbps systems from equipment makers use two carriers (each carrying 50Gbps) in a 50GHz channel, and while such equipment requires lower-speed electronics, twice as many coherent transmitters and receivers are needed overall.
Alcatel-Lucent is one vendor that has a single-carrier 50GHz system and so has Huawei. Ciena via its Nortel acquisition offers a dual-carrier 100Gbps system, as does Infinera. With Ciena's announcement of its WaveLogic 3 chipset, it is now moving to a single-carrier solution. Now Cisco is entering the market with a single-carrier system.
"When you have a single carrier, you can get upwards of 96 channels of 100Gbps in the C-band," says Nehib. "The equation here is about price, performance, density and power."
What has been done
Cisco's 100Gbps design fits on a 1RU (rack unit) card and uses the first 100Gbps coherent receiver ASIC designed by the CoreOptics team acquired by Cisco in May 2010.
The demonstrated 3,000km reach was made using low-loss fibre. "This is to some degree a hero experiment," says Nehib. "We have achieved 3,000km with SMF ULL fibre from Corning; the LL is low loss." Normal fibre has a loss of 0.20-0.25dB/km while for ULL fibre it is in the 0.17dB/km range.
"You can do the maths and calculate the loss we are overcoming over 3,000km. We just want to signal that we have very good performance for ultra long-haul," says Nehib, who admits that results will vary in networks, depending on the fibre.
Nehib says Cisco's coherent receiver achieves a chromatic dispersion tolerance of 70,000 ps/nm and 100ps differential group delay. Differential group delay is a non-linear effect, says Nehib, that is overcome using the DSP-ASIC. The greater the group delay tolerance, the better the distance performance. These metrics, claims Cisco, are currently unmatched in the industry.
The company has not said what CMOS process it is using for its ASIC design. But this is not the main issue, says Nehib: "We are trying to develop a part that is small so that it fits in many different platforms, and we can now use a single part number to go from metro performance all the way to ultra long-haul."
Another factor that impacts span performance is the number of lit channels. Cisco, in the test performed by independent test lab EANTC, the European Advanced Network Test Center, used 70 wavelengths. "With 70 channels the performance would have been very close to what we would have achieved with [a full complement of] 80 channels," says Nehib.
Super-channels
A super-channel refers to a signal made up of several wavelengths. Infinera, with its DTN-X, uses a 500Gbps super-channel, comprising five 100Gbps wavelengths.
Using a super-channel, an operator can turn up multiple 100Gbps channels at once. If an operator wants to add a 100Gbps wavelength, a client interface is simply added to a spare 100Gbps wavelength making up the super-channel. In contrast turning up a 100Gbps wavelength in current systems usually requires several days of testing to ensure it can carry live traffic alongside existing links.
Another benefit of super-channels is scale by turning up multiple wavelengths simultaneously. As traffic grows so does the work load on operators' engineering teams. Super-channels aid efficiency.
"There is one other point that we hear quite often," says Nehib. "One other attraction of super-channels is overall spectral efficiency." The carriers that make up the signal can be packed more closely, expanding overall fibre capacity.
"Just like with 10 Gig, we think at some point in the future the 100 Gig network will be depleted, especially in the largest networks, and operators will be interested in 400 Gig and Terabit interfaces," says Nehib. "If that wavelength can further benefit from advanced modulation schemes and super-channels through flex[ible] spectrum deployment then you can get more total bandwidth on the fibre and better utilisation of your amplifiers."
Cisco's 100Gbps lab demonstration also showed 400 Gigabit and 1 Terabit super-channels, part of its research work with the Politechnico di Torino. "We are going to move on to other advanced modulation techniques and deliver 400 Gigabit and Terabit interfaces in future," says Nehib.
Existing 100Gbps systems use dual-polarisation, quadrature phase-shift keying (DP-QPSK). Using 16-QAM (quadrature amplitude modulation) at the same baud rate doubles the data rate. Using 16-QAM also benefits spectral utilisation. If the more intelligent modulation format is used in a super-channel format, and the signal is fitted in the most appropriate channel spacing using flexible spectrum ROADMs, overall capacity is increased. However, the spectral efficiency of 16-QAM comes at the expense of overall reach.
"You are able to best match the rate to the reach to the spectrum," says Nehib. "The days of a single modulation scheme on a part are probably going to come to an end in the next two to three years."
Cisco has yet to discuss the addition of a coherent transmitter DSP which through spectral shaping can bunch wavelengths. Such an approach has just been detailed by Ciena with its WaveLogic 3 and Alcatel-Lucent with its 400 Gig photonic service engine.
For the Terabit super-channel demonstration, Cisco used 16-QAM and a flexible spectrum multiplexer. "The demo that we showed is not necessarily indicative of the part we will bring to market," says Nehib, pointing out that it is still early in the development cycle. "We are looking at the spectral efficiency of super-channels, different modulation schemes, flex-spectrum multiplexer, availability, quality, loss etc.," says Nehib. "We have not made firm technology choices yet."
Cisco's 100Gbps system is in trials with some 40 customers and can be ordered now. The product will be generally available in the near future, it says.
Further reading:
Light Reading: EANTC's independent test of Cisco's CloudVerse architecture. Part 4: Long-haul optical transport
Reflections 2011, Predictions 2012 - Part 2
Gazettabyte asked industry analysts, CEOs, executives and commentators to reflect on the last year and comment on developments they most anticipate for 2012. Here are the views of Verizon's Glenn Wellbrock, Professor Rod Tucker, Ciena's Joe Berthold, Opnext's Jon Anderson, NeoPhotonics' Tim Jenks and Vladimir Kozlov of LightCounting.
Glenn Wellbrock, Verizon's director of optical transport network architecture & design
The most significant accomplishment from an optical transport perspective for me was the introduction of 100 Gigabit into Verizon's domestic - US - network.
"The key technology enabler in 2012 will be the flexible grid optical switching that can support data rates beyond 100 Gigabit"
That accomplishment has paved the way for us to hit the ground running in 2012 with a very aggressive 100 Gigabit deployment plan. I also believe this accomplishment gives others the confidence to start taking advantage of this leading-edge technology.
With coherent receiver technology and the associated high-speed electronics lowering the propagation latency by up to 15%, we see a much cleaner line system design that eliminates external dispersion compensation fibre while bringing down the cost, space and power per bit.
The value of the whole industry moving in this direction means higher volumes and, therefore, lower costs. This new infrastructure will allow operators to get ahead of customer demand, thus improving delivery intervals and introducing new, higher bandwidth services to those large key customers that require it.
In my opinion, the key technology enabler in 2012 will be the flexible grid optical switching that can support data rates beyond 100 Gigabit and provides the framework to support colourless, directionless and contentionless optical nodes.
Today, field technicians must plug a new transmitter/ receiver into the appropriate direction and filter port at both circuit ends. With this new technology, operations personnel can simply plug the new card into the next available port and it can then be provisioned, tested and even moved to a new colour or direction remotely without any on-site personnel involvement - even when there are multiple copies of the same colour on the same add/ drop structure coming from different fibres.
This new nodal architecture takes advantage of the inherent channel selection capability of the coherent receiver to eliminate fixed filters and opens up the door for a truly reconfigurable optical add/ drop multiplexer (ROADM) - creating new flexibility that can be used for optical restoration, network defragmentation, operational simplicity, and more.
Rod Tucker, Director of the Institute for a Broadband Enabled Society (IBES), Director of the Centre for Energy-Efficient Telecommunications (CEET), and professor of electrical and electronic engineering at the University of Melbourne.
Australia's National Broadband Network (NBN) hit the ground running in 2011.
The project is still many years from completion, but in 2011 the roll-out of fibre-to-the-premises infrastructure began in earnest. This is a very noteworthy project - a wholesale broadband access network delivering advanced broadband services to the entire population of the country, including fibre to 93% of all premises and a mixture of fixed wireless and satellite to the remainder. At an estimated cost of around AUS$36 billion, the price tag is not small.
"The environment created by [Australia's] National Broadband Network will greatly enhance opportunities for innovations in new services and new modes of broadband service delivery"
But the wholesale-only model maximises opportunities for competition at the service provider level, and reduces wasteful duplication of infrastructure in the last mile. A remarkable aspect of the NBN project is that a deal has been struck between the incumbent telco, Telstra, and the government-owned owner of the NBN.
Under this deal, Telstra will shut down its Hybrid-Fibre-Coax (HFC) network and decommission its legacy copper access network. Australia will become a truly fibre-connected country, with a future-proof broadband infrastructure.
My thoughts for 2012 also relate to Australia's National Broadband Network. The environment created by the NBN will greatly enhance opportunities for innovations in new services and new modes of broadband service delivery.
I anticipate that in 2012 and beyond, new services providers and aggregators in areas such as health care, education, entertainment and energy will emerge.
I am very excited about the opportunities.
Joe Berthold, vice president of network architecture at Ciena
One of the most memorable developments from a network architecture point of view was the clear emergence of the category of packet-optical switching products to serve as the transport layer of backbone IP networks.
For years two competing points of view have been put forth. First, in the 'IP-over-glass' position, long-haul optics is incorporated into core routers. This has never taken off, with some disappointing attempts in the early days of 40 Gigabit. The second approach involves a separate, very much simpler, packet optical transport platform being introduced to interconnect core routers. The packet transport could be based on Ethernet protocols, MPLS, MPLS-TE or MPLS-TP.
"It will be interesting to see if a large internet data centre operator decides to embrace the OpenFlow concept at this very early stage of its development"
What is quite significant in this development, traditional router vendors seem to be going in this direction too, with the vision of a much simpler packet switching platform to keep cost, space and power under control.
This is a clear response to the overwhelming need we see in the market, representing a separation of packet switching into two layers: one with global routing capability at strategic locations in the network, and the other with flexible transport functionality for network traffic engineering.
In 2012 it will be fascinating to see how the struggle for protocol dominance plays out within the data centre.
While the IETF has many competing proposals, worked in multiple groups, the IEEE is in final ballot now for Shortest Path Bridging (IEEE 802.1aq).
Shortest Path Bridging has broad applicability in networks, but we might see it first emerge as a solution within the data centre.
The other contender within the data centre is OpenFlow, which has developed quite a momentum too.
It will be interesting to see if a large internet data centre operator decides to embrace the OpenFlow concept at this very early stage of its development.
Jon Anderson, director of technology programme at Opnext
Our most significant 2011 events were the Japan great earthquake in March and the Thailand floods in October. Both events caused major disruptions and challenges in optical component supply-chain management and manufacturing.
JDS Uniphase's tunable SFP+ announcement was well ahead of the technology curve.
"Our most significant 2011 events were the Japan great earthquake in March and the Thailand floods in October."
In 2012 we expect initial production shipments and deployment of 100Gbps PM-QPSK/ coherent modules. Also a fast production ramp of 40 Gigabit Ethernet (GbE) QSFP+ modules for data centre applications.
Another development to watch is the next-generation 100 GbE interconnect technology and standards development for low-cost, high-density modules for data centre applications.
Lastly, there will be an increased focus on technologies and solutions for 100 Gigabit DWDM in metro and extended reach enterprise applications.
Tim Jenks, CEO of NeoPhotonics
NeoPhotonics made significant progress this year in developments of components and technologies for coherent transmission networks, including receivers, transmitters and advanced approaches toward switching.
We continue to see increasing adoption of coherent transmission systems, broad-scale deployment of access networks and a continuing emergence of large scale data centres as a prominent element of the communications network landscape.
Vladimir Kozlov, CEO of LightCounting
The industry was strong enough to get over an earthquake, tsunami and flood in 2011. Softer demand for optics in 2011 helped - is still helping - many vendors to ride the disruptions. Ironically, the industry was more stressed ramping up production in 2010 to meet demand than dealing with the disruptions of 2011. We are looking forward to a smoother ride in 2012, as demand/ supply reach equilibrium and nature cooperates.
"Ironically, the industry was more stressed ramping up production in 2010 to meet demand than dealing with the disruptions of 2011"
Service provider revenue and capex were up significantly in 2011. Mobile data is driving the growth, but even wireline revenues are improving and FTTx is probably behind it. This should be a sustainable trend for 2012-2015, even as service providers curb expenses to improve profitability, a larger fraction of capex will be spend on equipment. New technology is critical to stay ahead of competition.
Data centre optics had another good year with 10GBASE-T falling further behind schedule and with 100 Gigabit generating much action. This will probably get even more interesting in 2012.
Our conservative forecast for active optical cable, criticised by some vendors, was not conservative enough in 2011. It will take a while for this segment to unfold.
For Part 1, click here
For Part 3, click here
ROADMs: core role, modest return for component players
Next-generation reconfigurable optical add/ drop multiplexers (ROADMs) will perform an important role in simplifying network operation but optical component vendors making the core component - the wavelength-selective switch (WSS) - on which such ROADMs will be based should expect a limited return for their efforts.
"[Component suppliers] are going to be under extreme constraints on pricing and cost"
Sterling Perrin, Heavy Reading
That is one finding from an upcoming report by market research firm, Heavy Reading, entitled: "The Next-Gen ROADM Opportunity: Forecast & Analysis".
"We do see a growth opportunity [for optical component vendors]," says Sterling Perrin, senior analyst and author of the report. “But in terms of massive pools of money becoming available, it's not going to happen; it is a modest growth in spend that will go to next-generation ROADMs."
That is because operators’ capex spending on optical will grow only in single digits annually while system vendors that supply the next-generation ROADMs will compete fiercely, including using discounting, to win this business. "All of this comes crashing down on the component suppliers, such that they are going to be under extreme constraints on pricing and cost," says Perrin. The report will quantify the market opportunity but Heavy Reading will not discuss numbers until the report is published.
Next-generation ROADMs incorporate such features as colourless (wavelength-independence on an input port), directionless (wavelength routing to any port), contentionless (more than one same-wavelength light path accommodated at a port) and flexible spectrum (variable channel width for signal rates above 100 Gigabit-per-second (Gbps)).
Networks using such ROADMs promise to reduce service providers' operational costs. And coupled with the wide deployment of coherent optical transmission technology, next-generation ROADMs are set to finally deliver agile optical networks.
Other of the report’s findings include the fact that operators have been deploying colourless and directionless ROADMs since 2010, even though implementing such features using current 1x9 WSSs are cumbersome and expensive. However, operators wanting these features in their networks have built such systems with existing components. "Probably about 10% of the market was using colourless and directionless functions in 2010," says Perrin.
Service providers are requiring ROADMs to support flexible spectrum even though networks will likely adopt light paths faster than 100Gbps (400Gbps and beyond) in several years' time.
The need to implement a flexible spectrum scheme will force optical component vendors with microelectromechanical system (MEMS) technology to adopt liquid crystal technology – and liquid-crystal-on-silicon (LCoS) in particular - for their WSSs (see Comments). "MEMS WSS technology is great for all the stuff we do today - colourless, directionless and contentionless - but when you move to flexible spectrum it is not capable of doing that function," says Perrin. "The technology they (vendors with MEMS technology) have set their sights on - and which there is pretty much agreement as the right technology for flexible spectrum - is the liquid crystal on silicon." A shift from MEMS to LCoS for next-generation ROADM technology is thus to be expected, he says.
Perrin also highlights how coherent detection technology, now being installed for 100 Gbps optical transmission, can also implement a colourless ROADM by making use of the tunable nature of the coherent receiver. "It knocks out a bunch of WSSs added to the add/ drop," says Perrin. "It is giving a colourless function for free, which is a huge advantage."
Perrin views next-gen ROADMs as a money-saving exercise for the operators, not a money-making one. "This is hitting on the capex as well as the opex piece which is absolutely critical," he says. "You see the charts of the hockey stick of bandwidth growth and flat venue growth; that is what ROADMS hit at."
The Heavy Reading report will be published later this month.
Further reading: