The CDFP 400 Gig module
- The CDFP will be a 400 Gig short reach module
- Module will enable 4 Terabit line cards
- Specification will be completed in the next year
A CDFP pluggable multi-source agreement (MSA) has been created to develop a 400 Gigabit module for use in the data centre. "It is a pluggable interface, very similar to the QSFP and CXP [modules]," says Scott Sommers, group product manager at Molex, one of the CDFP MSA members.
Scott Sommers, MolexThe CDFP name stands for 400 (CD in Roman numerals) Form factor Pluggable. The MSA will define the module's mechanical properties and its medium dependent interface (MDI) linking the module to the physical medium. The CDFP will support passive and active copper cable, active optical cable and multi-mode fibre.
"The [MSA member] companies realised the need for a low cost, high density 400 Gig solution and they wanted to get that solution out near term," says Sommers. Avago Technologies, Brocade Communications Systems, IBM, JDSU, Juniper Networks, TE Connectivity along with Molex are the founding members of the MSA.
Specification
Samples of the 400 Gig MSA form factor have already been shown at the ECOC 2013 exhibition held in September 2013, as were some mock active optical cable plugs.
"The width of the receptacle - the width of the active optical cable that plugs into it - is slightly larger than a QSFP, and about the same width as the CFP4," says Sommers. This places the width of the CDFP at around 22mm. The CDFP however will use 16, 25 Gigabit electrical lanes instead of the CFP4's four.
"We anticipate a pitch-to-pitch such that we could get 11 [pluggables] on one side of a printed circuit board, and there is nothing to prohibit someone doing belly-to-belly," says Sommers. Belly-to-belly refers to a double-mount PCB design; modules mounted double sidedly. Here, 22 CDFPs would achieve a capacity of 8.8 Terabits.
The MSA group has yet to detail the full dimensions of the form factor nor has it specified the power consumption the form factor will accommodate. "The target applications are switch-to-switch connections so we are not targeting the long reach market that require bigger, hotter modules," says Sommers. This suggests a form factor for distances up to 100m and maybe several hundred meters.
The MSA members are working on a single module design and there is no suggestion of future additional CDFP form factors as this stage.
"The aim is to get this [MSA draft specification] out soon, so that people can take this work and expand upon it, maybe at the IEEE or Infiniband," says Sommers. "Within a year, this specification will be out and in the public domain."
Meanwhile, companies are already active on designs using these building blocks. "In a complex MSA like this, there are pieces such as silicon and connectors that all have to work together," says Sommers.
100 Gigabit and packet optical loom large in the metro
"One hundred Gig metro has become critical in terms of new [operator] wins"
Michael Adams, Ciena
Ciena says operator interest in 100 Gigabit for the metro has been growing significantly.
"One hundred Gig metro has become critical in terms of new [operator] wins," says Michael Adams, vice president of product and technical marketing at Ciena. "Another request is integrated packet switching and OTN (Optical Transport Network) switching to fill those 100 Gig pipes."
The operator CenturyLink announced recently it had selected Ciena's 6500 packet optical transport platform for its network spanning 50 metropolitan regions.
The win is viewed by Ciena as significant given CenturyLink is the third largest telecommunications company in the US and has a global network. "We have already deployed Singapore, London and Hong Kong, and a few select US metropolitans and we are rolling that out across the country," says Adams.
Ciena says CenturyLink wants to offer 1, 10 and 100 Gigabit Ethernet (GbE) services. "In terms of the RFP (request for proposal) process with CenturyLink for next generation metro, the 100 Gigabit wavelength service was key and an important part of the [vendor] selection process."
The vendor offers different line cards based on its WaveLogic 3 coherent chipset depending on a metro or long haul network's specifications. "We firmly believe that 100 Gig coherent in the metro is going to be the way the market moves," says Adams.
At the recent OFC/NFOEC show, Ciena demonstrated WaveLogic 3 based production cards moving between several modulation formats, from binary phase-shift keying (BPSK) to quadrature PSK (QPSK) to 16-QAM (quadrature amplitude modulation).
Ciena showed a 16-QAM-based 400 Gig circuit using two, 200 Gig carriers. "With a flexible grid ROADM, the two [carriers] are pushed together into a spectral grid much less than 100GHz [wide]," says Adams.
The WaveLogic 3 features a transmit digital signal processor (DSP) as well as the receive DSP. "The transmit DSP is key to be able to move the frequencies to much less than 100GHz of spectrum in order to get greater than 20 Terabits [capacity] per fibre," says Adams. "With 88 wavelengths at 100 Gig that is 8.8 Terabits, and with 16-QAM that doubles to 17.6Tbps; we expect at least a [further] 20 percent uplift with the transmit DSP and gridless."
Adams says the company will soon detail the reach performance of its 400 Gig technology using 16-QAM.
It is still early in the market regarding operator demand for 400 Gig transmission. "2013 is the year for 100 Gig but customers always want to know that your platform can deliver the next thing," says Adams. "In the metro regional distances, we believe we can get a 50 percent improvement in economics using 16-QAM." That is because WaveLogic 3 can transmit 100GbE or 10x10GbE in a 50GHz channel, or double that - 2x100GbE or 20x10GbE - using 16-QAM modulation.
The system vendor is also one of AT&T's domain programme suppliers. Ciena will not expand on the partnership beyond saying there is close collaboration between the two. "We give them a lot of insight on roadmaps and on technology; they have a lot of opportunity to say where they would like their partner to be investing," says Adams.
Ciena came top in terms of innovation and leadership in a recent Heavy Reading survey of over 100 operators regarding metro packet-optical. Ciena was rated first, followed by Cisco Systems, Alcatel-Lucent and Huawei. "Our solid packet switching [on the 6500] is why CenturyLink chose us," says Adams.
Aurrion mixes datacom and telecom lasers on a wafer
"There is an inevitability of the co-mingling of electronics and optics and we are just at the beginning"
Eric Hall, Aurrion
Aurrion's long-term vision for its heterogeneous integration approach to silicon photonics is to tackle all stages of a communication link: the high-bandwidth transmitter, switch and receiver. Heterogeneous integration refers to the introduction of III-V material - used for lasers, modulators and receivers - onto the silicon wafer where it is processed alongside the silicon using masks and lithography.
In a post-deadline paper given at OFC/NFOEC 2013, the fabless start-up detailed the making of various transmitters on a silicon wafer. These include tunable lasers for telecom that cover the C- and L-bands, and uncooled laser arrays for datacom.
The lasers are narrow-linewidth tunable devices for long-haul coherent applications. According to Aurrion, achieving a narrow-linewidth laser typically requires an external cavity whose size makes it difficult to produce a compact design when integrated with the modulator.
Having a tunable laser integrated with the modulator on the same silicon photonics platform will enable compact 100 Gigabit coherent pluggable modules. "The 100 Gig equivalent of the tunable XFP or SFP+," says Eric Hall, vice president of business development at Aurrion.
Hall admits that traditional indium-phosphide laser manufacturers will likely integrate tunable lasers with the modulator to produce compact narrow-linewidth designs. "There will be other approaches but it is exciting that we can now make this laser and modulator on this platform," says Hall. "And it becomes very exciting when you make these on the same wafer as high-volume datacom components."
Aurrion's vision of a coherent transmitter and a 16-laser array made on the same wafer. Source: Aurrion
The wafer's datacom devices include a 4-channel laser array for 100GBASE-LR4 10km reach applications and a 400 Gigabit transmitter design comprising 2x8 wavelength division multiplexing (WDM) arrays for a 16x25Gbps design, each laser spaced 200GHz apart. These could be for 10km or 40km applications depending on the modulator used. "These arrays are for uncooled applications," says Hall. "The idea is these don't have to be coarse WDM but tighter-spaced WDM that hold their wavelength across 20-80oC."
Coarse WDM-based laser arrays do not require a thermo-electric cooler (TEC) but the larger spacing of the wavelengths makes it harder to design beyond 100 Gigabit, says Hall: "Being able to pack in a bunch of wavelengths yet not need a TEC opens up a lot of applications."
Such lasers coupled with different modulators could also benefit 100 Gigabit shorter-reach interfaces currently being discussed in the IEEE, including the possibility of multi-level modulation schemes, says the company.
Aurrion says it is seeing the trend of photonics moving closer to the electronics due to emerging applications.
"Electronics never really noticed photonics because it was so far away and suddenly photonics has encroached into its personal space," says Hall. "There is an inevitability of the co-mingling of electronics and optics and we are just at the beginning."
Cisco Systems demonstrates 100 Gigabit technologies
* Announces 100 Gigabit transmission over 4,800km
"CPAK helps accelerate the feasibility and cost points of deploying 100Gbps"
Stephen Liu, Cisco
Cisco Sytems has announced that its 100 Gigabit coherent module has achieved a reach of 4,800km without signal regeneration. The span was achieved in the lab and the system vendor intends to verify the span in a customer's network.
The optical transmission system achieved a reach of 3,000km over low-loss fibre when first announced in 2012. The extended reach is not a result of a design upgrade, rather the 100 Gigabit-per-second (Gbps) module is being used on a link with Raman amplification.
Cisco says it started shipping its 100Gbps coherent module in June 2012. "We have shipped over 2,000 100Gbps coherent dense WDM ports," says Sultan Dawood, marketing manager at Cisco. The 100Gbps ports include line-side 100Gbps interfaces integrated within Cisco's ONS 15454 multi-service transport platform and its CRS core router supporting its IP-over-DWDM elastic core architecture.
Cisco has also coupled the ASR 9922 series router to the ONS 15454. "We are extending what we have done for IP and optical convergence in the core," says Stephen Liu, director of market management at Cisco. "There is now a common solution to the [network] edge."
None of Cisco's customers has yet used 100Gbps over a 3,000km span, never mind 4,800km. But the reach achieved is an indicator of the optical transmission performance. "The [distance] performance is really a proxy for usefulness," says Liu. "If you take that 3,000km over low-loss fibre, what that buys you is essentially a greater degree of tolerance for existing fibre in the ground."
Much industry attention is being given to the next-generation transmission speeds of 400Gbps and one Terabit. This requires support for super-channels - multi-carrier signals to transmit 400Gbps and one Terabit as well as flexible spectrum to pack the multi-carrier signals efficiently across the fibre's spectrum. But Cisco argues that faster transmission is only one part of the engineering milestones to be achieved, especially when 100Gbps deployment is still in its infancy.
To benefit 100Gbps deployments, Cisco has officially announced its own CPAK 100Gbps client-side optical transceiver after discussing the technology over the last year. "CPAK helps accelerate the feasibility and cost points of deploying 100Gbps," says Liu.
CPAK
The CPAK is Cisco' first optical transceiver using silicon photonics technology following its acquisition of LightWire. The CPAK is a compact optical transceiver to replace the larger and more power hungry 100Gbps CFP interfaces.
The CPAK is being launched at the same time as many companies are announcing CFP2 multi-source agreement (MSA) optical transceiver products. Cisco stresses that the CPAK conforms to the IEEE 100GBASE-LR4 and -SR10 100Gbps standards. Indeed at OFC/NFOEC it is demonstrating the CPAK interfacing with a CFP2.
The CPAK will be used across several Cisco platforms but the first implementation is for the ONS 15454.
The CPAK transceiver will be generally available in the summer of 2013.
OFC/NFOEC 2013 to highlight a period of change
Next week's OFC/NFOEC conference and exhibition, to be held in Anaheim, California, provides an opportunity to assess developments in the network and the data centre and get an update on emerging, potentially disruptive technologies.
Source: Gazettabyte
Several networking developments suggest a period of change and opportunity for the industry. Yet the impact on optical component players will be subtle, with players being spared the full effects of any disruption. Meanwhile, industry players must contend with the ongoing challenges of fierce competition and price erosion while also funding much needed innovation.
The last year has seen the rise of software-defined networking (SDN), the operator-backed Network Functions Virtualization (NFV) initiative and growing interest in silicon photonics.
SDN has already being deployed in the data centre. Large data centre adopters are using an open standard implementation of SDN, OpenFlow, to control and tackle changing traffic flow requirements and workloads.
Telcos are also interested in SDN. They view the emerging technology as providing a more fundamental way to optimise their all-IP networks in terms of processing, storage and transport.
Carrier requirements are broader than those of data centre operators; unsurprising given their more complex networks. It is also unclear how open and interoperable SDN will be, given that established vendors are less keen to enable their switches and IP routers to be externally controlled. But the consensus is that the telcos and large content service providers backing SDN are too important to ignore. If traditional switching and routers hamper the initiative with proprietary add-ons, newer players will willing fulfill requirements.
Optical component players must assess how SDN will impact the optical layer and perhaps even components, a topic the OIF is already investigating, while keeping an eye on whether SDN causes market share shifts among switch and router vendors.
The ETSI Network Functions Virtualization (NFV) is an operator-backed initiative that has received far less media attention than SDN. With NFV, telcos want to embrace IT server technology to replace the many specialist hardware boxes that take up valuable space, consume power, add to their already complex operations support systems (OSS) while requiring specialist staff. By moving functions such as firewalls, gateways, and deep packet inspection onto cheap servers scaled using Ethernet switches, operators want lower cost systems running virtualised implementations of these functions.
The two-year NFV initiative could prove disruptive for many specialist vendors albeit ones whose equipment operate at higher layers of the network, removed from the optical layer. But the takeaway for optical component players is how pervasive virtualisation technology is becoming and the continual rise of the data centre.
Silicon photonics is one technology set to impact the data centre. The technology is already being used in active optical cables and optical engines to connect data centre equipment, and soon will appear in optical transceivers such as Cisco Systems' own 100Gbps CPAK module.
Silicon photonics promises to enable designs that disrupt existing equipment. Start-up Compass-EOS has announced a compact IP core router that is already running live operator traffic. The router makes use of a scalable chip coupled to huge-bandwidth optical interfaces based on 168, 8 Gigabit-per-second (Gbps) vertical-cavity surface-emitting lasers (VCSELs) and photodetectors. The Terabit-plus bandwidth enables all the router chips to be connected in a mesh, doing away with the need for the router's midplane and switching fabric.
The integrated silicon-optics design is not strictly silicon photonics - silicon used as a medium for light - but it shows how optics is starting to be used for short distance links to enable disruptive system designs.
Some financial analysts are beating the drum of silicon photonics. But integrated designs using VCSELs, traditional photonic integration and silicon photonics will all co-exist for years to come and even though silicon photonics is expected to make a big impact in the data centre, the Compass-EOS router highlights how disruptive designs can occur in telecoms.
Market status
The optical component industry continues to contend with more immediate challenges after experiencing sharp price declines in 2012.
The good news is that market research companies do not expect a repeat of the harsh price declines anytime soon. They also forecast better market prospects: The Dell'Oro Group expects optical transport to grow through 2017 at a compound annual growth rate (CAGR) of 10 percent, while LightCounting expects the optical transceiver market to grow 50 percent, to US $5.1bn in 2017. Meanwhile Ovum estimates the optical component market will grow by a mid-single-digit percent in 2013 after a contraction in 2012.
In the last year it has become clear how high-speed optical transport will evolve. The equipment makers' latest generation coherent ASICs use advanced modulation techniques, add flexibility by trading transport speed with reach, and use super-channels to support 400 Gigabit and 1 Terabit transmissions. Vendors are also looking longer term to techniques such as spatial-division multiplexing as fibre spectrum usage starts to approach the theoretical limit.
Yet the emphasis on 400 Gigabit and even 1 Terabit is somewhat surprising given how 100 Gigabit deployment is still in its infancy. And if the high-speed optical transmission roadmap is now clear, issues remain.
OFC/NFOEC 2013 will highlight the progress in 100 Gigabit transponder form factors that follow the 5x7-inch MSA, 100 Gigabit pluggable coherent modules, and the uptake of 100 Gigabit direct-detection modules for shorter reach links - tens or hundreds of kilometers - to connect data centres, for example.
There is also an industry consensus regarding wavelength-selective switches (WSSes) - the key building block of ROADMs - with the industry choosing a route-and-select architecture, although that was already the case a year ago.
There will also be announcements at OFC/NFOEC regarding client-side 40 and 100 Gigabit Ethernet developments based on the CFP2 and CFP4 that promise denser interfaces and Terabit capacity blades. Oclaro has already detailed its 100GBASE-LR4 10km CFP2 while Avago Technologies has announced its 100GBASE-SR10 parallel fibre CFP2 with a reach of 150m over OM4 fibre.
The CFP2 and QSFP+ make use of integrated photonic designs. Progress in optical integration, as always, is one topic to watch for at the show.
PON and WDM-PON remain areas of interest. Not so much developments in state-of-the-art transceivers such as for 10 Gigabit EPON and XG-PON1, though clearly of interest, but rather enhancements of existing technologies that benefit the economics of deployment.
The article is based on a news analysis published by the organisers before this year's OFC/NFOEC event.
OFC/NFOEC 2013: Technical paper highlights
Source: The Optical Society
Network evolution strategies, state-of-the-art optical deployments, next-generation PON and data centre interconnect are just some of the technical paper highlights of the upcoming OFC/NFOEC conference and exhibition, to be held in Anaheim, California from March 17-21, 2013. Here is a selection of the papers.
Optical network applications and services
Fujitsu and AT&T Labs-Research (Paper Number: 1551236) present simulation results of shared mesh restoration in a backbone network. The simulation uses up to 27 percent fewer regenerators than dedicated protection while increasing capacity by some 40 percent.
KDDI R&D Laboratories and the Centre Tecnològic de Telecomunicacions de Catalunya (CTTC), Spain (Paper Number: 1553225) show results of an OpenFlow/stateless PCE integrated control plane that uses protocol extensions to enable end-to-end path provisioning and lightpath restoration in a transparent wavelength switched optical network (WSON).
In invited papers, Juniper highlights the benefits of multi-layer packet-optical transport, IBM discusses future high-performance computers and optical networking, while Verizon addresses multi-tenant data centre and cloud networking evolution.
Network technologies and applications
A paper by NEC (Paper Number: 1551818) highlights 400 Gigabit transmission using four parallel 100 Gigabit subcarriers over 3,600km. Using optical Nyquist shaping each carrier occupies 37.5GHz for a total bandwidth of 150GHz.
In an invited paper Andrea Bianco of the Politecnico de Torino, Italy details energy awareness in the design of optical core networks, while Verizon's Roman Egorov discusses next-generation ROADM architecture and design.
FTTx technologies, deployment and applications
In invited papers, operators share their analysis and experiences regarding optical access. Ralf Hülsermann of Deutsche Telekom evaluates the cost and performance of WDM-based access networks, while France Telecom's Philippe Chanclou shares the lessons learnt regarding its PON deployments and details its next steps.
Optical devices for switching, filtering and interconnects
In invited papers, MIT's Vladimir Stojanovic discusses chip and board scale integrated photonic networks for next-generation computers. Alcatel-Lucent's Bell Labs' Nicholas Fontaine gives an update on devices and components for space-division multiplexing in few-mode fibres, while Acacia's Long Chen discusses silicon photonic integrated circuits for WDM and optical switches.
Optoelectronic devices
Teraxion and McGill University (Paper Number: 1549579) detail a compact (6mmx8mm) silicon photonics-based coherent receiver. Using PM-QPSK modulation at 28 Gbaud, up to 4,800 km is achieved.
Meanwhile, Intel and the UC-Santa Barbara (Paper Number: 1552462) discuss a hybrid silicon DFB laser array emitting over 200nm integrated with EAMs (3dB bandwidth> 30GHz). Four bandgaps spread over greater than 100nm are realised using quantum well intermixing.
Transmission subsystems and network elements
In invited Papers, David Plant of McGill University compares OFDM and Nyquist WDM, while AT&T's Sheryl Woodward addresses ROADM options in optical networks and whether to use a flexible grid or not.
Core networks
Orange Labs' Jean-Luc Auge asks whether flexible transponders can be used to reduce margins. In other invited papers, Rudiger Kunze of Deutsche Telekom details the operator's standardisation activities to achieve 100 Gig interoperability for metro applications, while Jeffrey He of Huawei discusses the impact of cloud, data centres and IT on transport networks.
Access networks
Roberto Gaudino of the Politecnico di Torino discusses the advantages of coherent detection in reflective PONs. In other invited papers, Hiroaki Mukai of Mitsubishi Electric details an energy efficient 10G-EPON system, Ronald Heron of Alcatel-Lucent Canada gives an update on FSAN's NG-PON2 while Norbert Keil of the Fraunhofer Heinrich-Hertz Institute highlights progress in polymer-based components for next-generation PON.
Optical interconnection networks for datacom and computercom
Use of orthogonal multipulse modulation for 64 Gigabit Fibre Channel is detailed by Avago Technologies and the University of Cambridge (Paper Number: 1551341).
IBM T.J. Watson (Paper Number: 1551747) has a paper on a 35Gbps VCSEL-based optical link using 32nm SOI CMOS circuits. IBM is claiming record optical link power efficiencies of 1pJ/b at 25Gb/s and 2.7pJ/b at 35Gbps.
Several companies detail activities for the data centre in the invited papers.
Oracle's Ola Torudbakken has a paper on a 50Tbps optically-cabled Infiniband data centre switch, HP's Mike Schlansker discusses configurable optical interconnects for scalable data centres, Fujitsu's Jun Matsui details a high-bandwidth optical interconnection for an densely integrated server while Brad Booth of Dell also looks at optical interconnect for volume servers.
In other papers, Mike Bennett of Lawrence Berkeley National Lab looks at network energy efficiency issues in the data centre. Lastly, Cisco's Erol Roberts addresses data centre architecture evolution and the role of optical interconnect.
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."
A FOX-C approach to flexible optical switching
Flexible switching of high-capacity traffic carried over ’super-channel' dense-wavelength division multiplexing wavelengths is the goal of the European Commission Seventh Framework Programme (FP7) research project.
The €3.6M FOX-C (Flexible optical cross-connect nodes) will develop a flexible spectrum reconfigurable optical add/drop multiplexer (ROADM) for 400Gbps and one Terabit optical transmission. The ROADM will be designed not only to switch super-channels but also the carrier constituent components.
Companies involved in the project include operator France Telecom and optical component player Finisar. However, no major European system vendor is taking part in the FOX-C project although W-Onesys, a small system vendor from Spain, is participating.
“We want to transfer to the optical layer the switching capability”
Erwan Pincemin, FT-Orange
“It is becoming more difficult to increase the spectral efficiency of such networks,” says Erwan Pincemin, senior expert in fibre optic transmission at France Telecom-Orange. “We want to increase the advantages of the network by adding flexibility in the management of the wavelengths in order to adapt the network as services evolve.”
FOX-C will increase the data rate carried by each wavelength to achieve a moderate increase in spectral efficiency. Pincemin says such modulation schemes as orthogonal frequency division multiplexing (OFDM) and Nyquist WDM will be explored. But the main goal is to develop flexible switching based on an energy efficient and cost effective ROADM design.
The ROADM’s filtering will be able to add and drop 10 and 100 Gigabit sub-channels or 400 Gigabit and 1 Terabit super-channels. By using the developed filter to switch optically at speeds as low as 10 Gigabit, the aim is to avoid having to do the switching electrically with its associated cost and power consumption overhead. “We want to transfer to the optical layer the switching capability,” says Pincemin.
While the ROADM design is part of the project’s goals, what is already envisaged is a two-stage pass-through-and-select architecture. The first stage, for coarse switching, will process the super-channels and will be followed by finer filtering to extract (drop) and insert (add) individual lower-rate tributaries.
The project started in Oct 2012 and will span three years. The resulting system testing will take place at France-Telecom Orange's Lab in Lannion, France.
Project players
The project’s technical leader is the Athens Institute of Technology (AIT), headed by Prof. Ioannis Tomkos, while the administrator leader is the Greek company Optronics Technologies.
Finisar will provide the two-stage optical switch while France Telecom-Orange will test the resulting ROADM and will build the multi-band OFDM transmitter and receiver to evaluate the design.
Athens Institute of Technology will work with Finisar on the technical aspects and in particular a flexible networking architecture study. The Hebrew University is working with Finisar on the design and the building of the ultra-selective adaptive optical filter, and has expertise is free-space optical systems. The Spanish firm, W-Onesys, is a system integration specialist and will also work with Finisar to integrate its wavelength-selective switch for the ROADM. Other project players include Aston University, Tyndall National Institute and the Karlsruhe Institute of Technology.
No major European system vendor is taking part in the FOX-C project. According to Pincemin this is regrettable although he points out that the equipment players are involved in other EC FP7 projects addressing flexible networking.
He believes that their priorities are elsewhere and that the FOX-C project may be deemed as too forward looking and risky. “They want to have a clear return on investment on their research,” says Pincemin.
The uphill battle to keep pace with bandwidth demand
Relative traffic increase normalised to 2010 Source: IEEE
Optical component and system vendors will be increasingly challenged to meet the expected growth in bandwidth demand.
According to a recent comprehensive study by the IEEE (The IEEE 802.3 Industry Connections Ethernet Bandwidth Assessment report), bandwidth requirements are set to grow 10x by 2015 compared to demand in 2010, and a further 10x between 2015 and 2020. Meanwhile, the technical challenges are growing for the vendors developing optical transmission equipment and short-reach high-speed optical interfaces.
Fibre bandwidth is becoming a scarce commodity and various techniques will be required to scale capacity in metro and long-haul networks. The IEEE is expected to develop the next-higher speed Ethernet standard to follow 100 Gigabit Ethernet (GbE) in 2017 only. The IEEE is only talking about capacities and not interface speeds. Yet, at this early stage, 400 Gigabit Ethernet looks the most likely interface.
"The various end-user markets need technology that scales with their bandwidth demands and does so economically. The fact that vendors must work harder to keep scaling bandwidth is not what they want to hear"
A 400GbE interface will comprise multiple parallel lanes, requiring the use of optical integration. A 400GbE interface may also embrace modulation techniques, further adding to the size, complexity and cost of such an interface. And to achieve a Terabit, three such interfaces will be needed.
All these factors are conspiring against what the various end-user bandwidth sectors require: line-side and client-side interfaces that scale economically with bandwidth demand. Instead, optical components, optical module and systems suppliers will have to invest heavily to develop more complex solutions in the hope of matching the relentless bandwidth demand.
The IEEE 802.3 Bandwidth Assessment Ad Hoc group, which produced the report that highlights the hundredfold growth in bandwidth demand between 2010 and 2020, studied several sectors besides core networking and data centre equipment such as servers. These include Internet exchanges, high-performance computing, cable operators (MSOs) and the scientific community.
The difference growth rates in bandwidth demand it found for the various sectors are shown in the chart above.
Optical transport
A key challenge for optical transport is that fibre spectrum is becoming a precious commodity. Scaling capacity will require much more efficient use of spectrum.
To this aim, vendors are embracing advanced modulation schemes, signal processing and complex ASIC designs. The use of such technologies also raises new challenges such as moving away from a rigid spectrum grid, requiring the introduction of flexible-grid switching elements within the network.
And it does not stop there.
Already considerable development work is underway to use multi-carriers - super-channels - whose carrier count can be adapted on-the-fly depending on demand, and which can be crammed together to save spectrum. This requires advanced waveform shaping based on either coherent orthogonal frequency division multiplexing (OFDM) or Nyquist WDM, adding further complexity to the ASIC design.
At present, a single light path can be increased from 100 Gigabit-per-second (Gbps) to 200Gbps using the 16-QAM amplitude modulation scheme. Two such light paths give a 400Gbps data rate. But 400Gbps requires more spectrum than the standard 50GHz band used for 100Gbps transmission. And using QAM reduces the overall optical transmission reach achieved.
The shorter resulting reach using 16-QAM or 64-QAM may be sufficient for metro networks (~1000km) but to achieve long-haul and ultra-long-haul spans will require super-channels based on multiple dual-polarisation, quadrature phase-shift keying (DP-QPSK) modulated carriers, each occupying 50GHz. Building up a 400Gbps or 1 Terabit signal this way uses 4 or 10 such carriers, respectively - a lot of spectrum. Some 8Tbps to 8.8Tbps long-haul capacity result using this approach.
The main 100Gbps system vendors have demonstrated 400Gbps using 16-QAM and two carriers. This doubles system capacity to 16-17.6Tbps. A further 30% saving in bandwidth using spectral shaping at the transmitter crams the carriers closer together, raising the capacity to some 23Tbps. The eventual adoption of coherent OFDM or Nyquist WDM will further boost overall fibre capacity across the C-band. But the overall tradeoff of capacity versus reach still remains.
Optical transport thus has a set of techniques to improve the amount of traffic it can carry. But it is not at a pace that matches the relentless exponential growth in bandwidth demand.
After spectral shaping, even more complex solutions will be needed. These include extending transmission beyond the C-band, and developing exotic fibres. But these are developments for the next decade or two and will require considerable investment.
The various end-user markets need technology that scales with their bandwidth demands and does so economically. The fact that vendors must work harder to keep scaling bandwidth is not what they want to hear.
"No-one is talking about a potential bandwidth crunch but if it is to be avoided, greater investment in the key technologies will be needed. This will raise its own industry challenges. But nothing like those to be expected if the gap between bandwidth demand and available solutions grows"
Higher-speed Ethernet
The IEEE's Bandwidth Assessment study lays the groundwork for the development of the next higher-speed Ethernet standard.
Since the standard work has not yet started, the IEEE stresses that it is premature to discuss interface speeds. But based on the state of the industry, 400GbE already looks the most likely solution as the next speed hike after 100GbE. Adopting 400GbE, several approaches could be pursued:
- 16 lanes at 25Gbps: 100GbE is moving to a 4x25Gbps electrical interface and 400GbE could exploit such technology for a 16-lane solution, made up of four, 4x25Gbps interfaces. "If I was a betting man, I'd probably put better odds on that [25Gbps lanes] because it is in the realm of what everyone is developing," John D'Ambrosia, chair of the IEEE 802.3 Industry Connections Higher Speed Ethernet Consensus group and chair of the the IEEE 802.3 Bandwidth Assessment Ad Hoc group, told Gazettabyte.
- 10 lanes at 40Gbps: The Optical Internetworking Forum (OIF) has started work on an electrical interface operating between 39 and 56Gbps (Common Electrical Interface - 56G-Close Proximity Reach). This could lead to 40Gbps lanes and a 10x40Gbps implementation for a 400Gbps Ethernet design.
- Modulation: For the 100Gbps backplane initiative, the IEEE is working on pulse-amplitude modulation (PAM), says D'Ambrosia. Such modulation could be used for 400GbE. Modulation is also being considered by the IEEE to create a single-lane 100Gbps interface. Such a solution could lead to a 4-lane 400GbE solution. But adopting modulation comes at a cost: more sophisticated electronics, greater size and power consumption.
As with any emerging standard, first designs will be large, power-hungry and expensive. The industry will have to work hard to produce more integrated 16-lane or 10-lane designs. Size and cost will also be important given that three 400GbE modules will be needed to implement a Terabit interface.
The challenge for component and module vendors is to develop such multi-lane designs yet do so economically. This will require design ingenuity and optical integration expertise.
Timescales
Super-channels exist now - Infinera is shipping its 5x100Gbps photonic integrated circuit. Ciena and Alcatel-Lucent are introducing their latest generation DSP-ASICs that promise 400Gbps signals and spectral shaping while other vendors have demonstrated such capabilities in the lab.
The next Ethernet standard is set for completion in 2017. If it is indeed based on a 400GbE Ethernet interface, it will likely use 4x25Gbps components for the first design, benefiting from emerging 100GbE CFP2 and CFP4 modules and their more integrated designs. But given the standard will only be completed in five years' time, new developments should also be expected.
No-one is talking about a potential bandwidth crunch but if it is to be avoided, greater investment in the key technologies will be needed. This will raise its own industry challenges. But nothing like those to be expected if the gap between bandwidth demand and available solutions grows.
Briefing: Flexible elastic-bandwidth networks
Vendors and service providers are implementing the first examples of flexible, elastic-bandwidth networks. Infinera and Microsoft detailed one such network at the Layer123 Terabit Optical and Data Networking conference held earlier this year.
Optical networking expert Ioannis Tomkos of the Athens Information Technology Center explains what is flexible, elastic bandwidth.
Part 1: Flexible elastic bandwidth
"We cannot design anymore optical networks assuming that the available fibre capacity is abundant"
Prof. Tomkos
Several developments are driving the evolution of optical networking. One is the incessant demand for bandwidth to cope with the 30+% annual growth in IP traffic. Another is the changing nature of the traffic due to new services such as video, mobile broadband and cloud computing.
"The characteristics of traffic are changing: A higher peak-to-average ratio during the day, more symmetric traffic, and the need to support higher quality-of-service traffic than in the past," says Professor Ioannis Tomkos of the Athens Information Technology Center.
"The growth of internet traffic will require core network interfaces to migrate from the current 10, 40 and 100Gbps to 1 Terabit by 2018-2020"
Operators want a more flexible infrastructure that can adapt to meet these changes, hence their interest in flexible elastic-bandwidth networks. The operators also want to grow bandwidth as required while making best use of the fibre's spectrum. They also require more advanced control plane technology to restore the network elegantly and promptly following a fault, and to simplify the provisioning of bandwidth.
The growth of internet traffic will require core network interfaces to migrate from the current 10, 40 and 100Gbps to 1 Terabit by 2018-2020, says Tomkos. Such bit-rates must be supported with very high spectral efficiencies, which according to latest demonstrations are only a factor of 2 away of the Shannon's limit. Simply put, optical fibre is rapidly approaching its maximum limit.
"We cannot design anymore optical networks assuming that the available fibre capacity is abundant," says Tomkos. "As is the case in wireless networks where the available wireless spectrum/ bandwidth is a scarce resource, the future optical communication systems and networks should become flexible in order to accommodate more efficiently the envisioned shortage of available bandwidth.”
The attraction of multi-carrier schemes and advanced modulation formats is the prospect of operators modifying capacity in a flexible and elastic way based on varying traffic demands, while maintaining cost-effective transport.
Elastic elements
Optical systems providers now realise they can no longer keep increasing a light path's data rate while expecting the signal to still fit in the standard International Telecommunication Union (ITU) - defined 50GHz band.
It may still be possible to fit a 200 Gigabit-per-second (Gbps) light path in a 50GHz channel but not a 400Gbps or 1 Terabit signal. At 400Gbps, 80GHz is needed and at 1 Terabit it rises to 170GHz, says Tomkos. This requires networks to move away from the standard ITU grid to a flexible-based one, especially if operators want to achieve the highest possible spectral efficiency.
Vendors can increase the data rate of a carrier signal by using more advanced modulation schemes than dual polarisation, quadrature phase-shift keying (DP-QPSK), the defacto 100Gbps standard. Such schemes include amplitude modulation at 16-QAM, 64-QAM and 256-QAM but the greater the amplitude levels used and hence the data rates, the shorter the resulting reach.
Another technique vendors are using to achieve 400Gbps and 1Tbps data rates is to move from a single carrier to multiple carriers or 'super-channels'. Such an approach boosts the data rate by encoding data on more than one carrier and avoids the loss in reach associated with higher order QAM. But this comes at a cost: using multiple carriers consumes more, precious spectrum.
As a result, vendors are looking at schemes to pack the carriers closely together. One is spectral shaping. Tomkos also details the growing interest in such schemes as optical orthogonal frequency division multiplexing (OFDM) and Nyquist WDM. For Nyquist WDM, the subcarriers are spectrally shaped so that they occupy a bandwidth close or equal to the Nyquist limit to avoid inter symbol interference and crosstalk during transmission.
Both approaches have their pros and cons, says Tomkos, but they promise optimum spectral efficiency of 2N bits-per-second-per-Hertz (2N bits/s/Hz), where N is the number of constellation points.
The attraction of these techniques - multi-carrier schemes and advanced modulation formats - is the prospect of operators modifying capacity in a flexible and elastic way based on varying traffic demands, while maintaining cost-effective transport.
"With flexible networks, we are not just talking about the introduction of super-channels, and with it the flexible grid," says Tomkos. "We are also talking about the possibility to change either dynamically."
According to Tomkos, vendors such as Infinera with its 5x100Gbps super-channel photonic integrated circuit (PIC) are making an important first step towards flexible, elastic-bandwidth networks. But for true elastic networks, a flexible grid is needed as is the ability to change the number of carriers on-the-fly.
"Once we have those introduced, in order to get to 1 Terabit, then you can think about playing with such parameters as modulation levels and the number of carriers, to make the bandwidth really elastic, according to the connections' requirements," he says.
Meanwhile, there are still technology advances needed before an elastic-bandwidth network is achieved, such as software-defined transponders and a new advanced control plane.
Tomkos says that operators are now using control plane technology that co-ordinates between layer three and the optical layer to reduce network restoration time from minutes to seconds. Microsoft and Infinera cite that they have gone from tens of minutes down to a few seconds using the more advanced optical infrastructure. "They [Microsoft] are very happy with it," says Tomkos.
But to provision new capacity at the optical layer, operators are talking about requirements in the tens of minutes; something they do not expect will change in the coming years. "Cloud services could speed up this timeframe," says Tomkos.
"There is usually a big lag between what operators and vendors do and what academics do," says Tomkos. "But for the topic of flexible, elastic networking, the lag between academics and the vendors has become very small."
Further reading: