Ciena: Changing bandwidth on the fly
Ciena has announced its latest coherent chipset that will be the foundation for its future optical transmission offerings. The chipset, dubbed WaveLogic 3, will extend the performance of its 100 Gigabit links while introducing transmission flexibility that will trade capacity with reach.
Feature: Beyond 100 Gigabit - Part 1
"We are going to be deployed, [with WaveLogic 3] running live traffic in many customers’ networks by the end of the year"
Michael Adams, Ciena
"This is changing bandwidth modulation on the fly," says Ron Kline, principal analyst, network infrastructure group at market research firm, Ovum. “The capability will allow users to dynamically optimise wavelengths to match application performance requirements.”
WaveLogic 3 is Ciena's third-generation coherent chipset that introduces several firsts for the company.
- The chipset supports single-carrier 100 Gigabit-per-second (Gbps) transmission in a 50GHz channel.
- The chipset includes a transmit digital signal processor (DSP) - which can adapt the modulation schemes as well as shape the pulses to increase spectral efficiency. The coherent transmitter DSP is the first announced in the industry.
- WaveLogic 3's second chip, the coherent receiver DSP, also includes soft-decision forward error correction (SD-FEC). SD-FEC is important for high-capacity metro and regional, not just long-haul and trans-Pacific routes, says Ciena.
The two-ASIC chipset is implemented using a 32nm CMOS process. According to Ciena, the receiver DSP chip, which compensates for channel impairments, measures 18 mm sq. and is capable of 75 Tera-operations a second.
Ciena says the chipset supports three modulation formats: dual-polarisation bipolar phase-shift keying (DP-BPSK), quadrature phase-shift keying (DP-QPSK) and 16-QAM (quadrature amplitude modulation). Using a single carrier, these equate to 50Gbps, 100Gbps and 200Gbps data rates. Going to 16-QAM may increase the data rate to 200Gbps but it comes at a cost: a loss in spectral efficiency and in reach.
"This software programmability is critical for today's dynamic, cloud-centric networks," says Michael Adams, Ciena’s vice president of product & technology marketing.
WaveLogic 3 has also been designed to scale to 400Gbps. "This is the first programmable coherent technology scalable to 400 Gig," says Adams. "For 400 Gig, we would be using a dual-carrier, dual-polarisation 16-QAM that would use multiple [WaveLogic 3] chipsets."
Performance
Ciena stresses that this is a technology not a product announcement. But it is willing to detail that in a terrestrial network, a single carrier 100Gbps link using WaveLogic 3 can achieve a reach of 2,500+ km. "These refer to a full-fill [wavelengths in the C-Band] and average fibre," says Adams. "This is not a hero test with one wavelength and special [low-loss] fibre.”
Metro to trans-Pacific: The different reaches and distances over terrestrial and submarine using Ciena's WaveLogic 3. SC stands for single carrier. Source: Ciena/ Gazettabyte
When the modulation is changed to BPSK, the reach is effectively doubled. And Ciena expects a 9,000-10,000km reach on submarine links.
The same single-carrier 50GHz channel reverting to 16-QAM can transmit a 200Gbps signal over distances of 750-1,000km. "A modulation change [to 16-QAM] and adding a second 100 Gigabit Ethernet transceiver and immediately you get an economic improvement," says Adams.
For 400Gbps, two carriers, each 16-QAM, are needed and the distances achieved are 'metro regional', says Ciena.
The transmit DSP also can implement spectral shaping. According to Ciena, by shaping the signals sent, a 20-30% bandwidth improvement (capacity increase) can be achieved. However that feature will only be fully exploited once networks deploy flexible grid ROADMs.
At OFC/NFOEC. Ciena will be showing a prototype card that will demonstrate the modulation going from BPSK to QPSK to 16-QAM. "We are going to be deployed, running live traffic in many customers’ networks by the end of the year," says Adams.
Analysis
Sterling Perrin, senior analyst, Heavy Reading
Heavy Reading believes Ciena's WaveLogic 3 is an impressive development, compared to its current WaveLogic 2 and to other available coherent chipsets. But Perrin thinks the most significant WaveLogic 3 development is Ciena’s single-carrier 100Gbps debut.
Until now, Ciena has used two carriers within a 50GHz, each carrying 50Gbps of data.
"The dual carrier approach gave Ciena a first-to-market advantage at 100Gbps, but we have seen the vendor lose ground as Alcatel-Lucent rolled out its single carrier 100Gbps system," says Perrin in a Heavy Reading research note. "We believe that Alcatel-Lucent was the market leader in 100Gbps transport in 2011."
Other suppliers, including Cisco Systems and Huawei, have also announced single-carrier 100Gbps, and more single-wavelength 100Gbps announcements will come throughout 2012.
Heavy Reading believes the ability to scale to 400Gbps is important, as is the use of multiple carriers (or super-channels). But 400 Gigabit and 1 Terabit transport are still years away and 100Gbps transport will be the core networking technology for a long time yet.
"The vendors with the best 100G systems will be best-positioned to capture share over the next five years, we believe," says Perrin.
Ron Kline, principal analyst for Ovum’s network infrastructure group.
For Ron Kline, Ciena's announcement was less of a surprise. Ciena showcased WaveLogic 3's to analysts late last year. The challenge with such a technology announcement is understanding the capabilities and how it will be rolled out and used within a product, he says.
"Ciena's WaveLogic 3 is the basis for 400 Gig," says Kline. "They are not out there saying 'we have 400 Gig'." Instead, what the company is stressing is the degree of added capacity, intelligence and flexibility that WaveLogic 3 will deliver. That said, Ciena does have trials planned for 400 Gig this year, he says.
What is noteworthy, says Ovum, is that 400Gbps is within Ciena's grasp whereas there are still some vendors yet to record revenues for 100Gbps.
"Product differentiation has changed - it used to be about coherent," says Kline. "But now that nearly all vendors have coherent, differentiation is going to be determined by who has the best coherent technology."
40 Gigabit Ethernet QSFPs boost port density and reach
"For the larger data centres being built today, reach is becoming more and more important"
I Hsing Tan, Avago
Avago’s eSR4 QSFP+ transceiver extends the reach of 40GbE over multimode fibre beyond the IEEE 40GBASE-SR4 specification, to 300m over OM3 and 400m over OM4 multimode fibre.
Reflex Photonics’ 40GbE QSFP also achieves 300m over OM3 fibre and while it has not tested the transceiver over OM4 fibre, the company is using the same optics that it uses for its CFP which meets 450m over OM4.
“This [QSFP] is aimed at large data centres operated by the likes of a Google or a Facebook,” says Robert Coenen, vice president, sales and marketing at Reflex Photonics. Such data centres can have link requirements of 1000m. “The more reach you can give over multimode fibre, the more money they [data centre operators] can save.”
The eSR4, like Avago's already announced iSR4 (interoperable SR4) 40GbE QSFP+ transceiver, supports either 40GbE or four independent 10GbE channels. When used as a multichannel 10GbE interface, the QSFP+ can interface to various 10GbE form factors such as X2, XFP and SFP+, says Avago.
The iSR4 also increases the faceplate port density of equipment from 48, 10 Gigabit Ethernet (GbE) SFP+ ports to up to 44 QSFP+ 40GbE ports. Avago says that one equipment vendor has already announced a card with 36 QSFP+ ports. The iSR4 QSFP+ also reduces the overall Gigabit/Watt power consumption to 37.5mW/Gbps compared to 100mW /Gbps for the SFP+. The eSR4 has half the power consumption, which puts it around 50mW/Gbps.
But the iSR4 matches the reach of the IEEE 40GBASE-SR4 40GbE standard: 100m for OM3 and 150m for OM4-based fibre. "This [reduced reach at 40GbE] creates an issue for data centre operations," says I Hsing Tan, Ethernet segment marketing manager in the fiber optics product division at Avago. "They require additional investment to redo all the wiring in current 10GbE infrastructure to support a shorter reach."
With the extended reach 40GbE QSFPs the reach associated with 10GbE interfaces on OM3 and OM4 multimode fibre is now restored.
The iSR4 module is available now, says Avago, while the eSR4 will be available from mid-2012. Reflex’s Coenen says it will have samples of its 40GbE QSFP, which also supports 40GbE and 4x10GbE, by May 2012.
What has been done
For Avago's iSR4 QSFP+ to operate as four, 10GbE channels, it has to comply with the 10GBASE-SR optical standard. That is because 10GBASE-SR supports a maximum receive power of -1dBm whereas the 40GBASE-SR4 has a maximum output power of 2.4dBm. The transmitter power of the iSR4 has thus been reduced. "We force the output of the transmitter down to -1dBm," says Tan.
To achieve the greater reach, the eSR4 uses a VCSEL design with a tighter spectral width. Other parameters include the optical modulation amplitude power and the wavelength. These affect the resulting fibre dispersion. “Once you control the spectral width, you can design the other two to meet the specs," says Tan.
The Avago 40GbE QSFP+ modules use an integrated 4- channel VCSEL array and a 4-channel photo-detector array.
Significance
The 40GbE short reach interfaces play an important role in the data centre. As servers move from using 1GbE to 10GbE interfaces, the uplink from aggregation 'top-of-rack' switches must also scale from 10GbE to higher speeds of 40GbE or 100GbE.
However existing 100GbE interfaces make use of the CFP module which is relatively large and expensive. And although the 100GbE standard has a clear roadmap leading to CFP2 and CFP4 modules, half and a quarter of the size of the CFP, respectively, these are not yet available.
40GbE QSFP+ transceivers do exist and offer the equipment faceplate density improvement vendors want.
The QSFP+ also benefits existing 10GbE designs by supporting nearly 4x the number of 10GbE on a card. Thus a new blade supporting up to 44, 40GbE QSFP+ transceivers can interface to up to 176 10GbE transceivers, a near fourfold capacity increase.
According to Avago, between 10% and 20% of interface requirements in the data centre are beyond 150m. Without the advent of extended reach 40GbE modules, data centre operators would need to deploy single mode fibre and a 40GBASE-LR4 module, it says. And while that can be fitted inside a QSFP, its power consumption is up to 3.5W, compared to the 1.5W of the QSFP+ eSR4. "The cost of the LR4 is also increased by at least a factor of three," says Tan.
Avago says that some 95% of all fibre in the data centre is multimode fibre. As for OM3 and OM4 deployments the ratio is 80% to 20%, respectively.