Alcatel-Lucent reveals its 100Gbps-coherent hand

“It would be irresponsible of any system vendor to overlook a solution that can bring a cost advantage to their customer”

Sam Bucci, Alcatel-Lucent

What is being announced?

• Alcatel-Lucent has a commercially available 100Gbps optical transmission system.
• 40Gbps coherent transmission is also supported.
• Implemented as part of the 1830 Photonic Service Switch (PSS), the platform has a capacity of 500 Gigabit-per-second (Gbps) per rack, or a bay – made up of three racks – capacity of 1.5 Terabit-per-second.
• The system specification includes 88, 100Gbps dense wavelength division multiplexing (DWDM) lightpaths at 50GHz spacing that span the extended C-band; a reach of between 1,500 and 2,000km using coherent-optimised optical amplifiers, and the ability to operate alongside existing 10 and 40Gbps wavelengths without needing a guard-band between them (for more detail, click here).
• Some 20 operators are lined up to trial the 100Gbps technology. These include operators that have deployed the 1830 PSS and new ones.
• Telefònica and Softbank Telecom are two operators known to be trialling the 100Gbps system, Alcatel-Lucent will announce a third next week.

Why is the announcement important?

Alcatel-Lucent is the latest system vendor to announce a commercially available 100Gbps system. Until now Nortel’s Metro Ethernet Networks unit, now owned by Ciena, and Ciena itself had commercially available systems. Indeed Verizon Business deployed Nortel’s 100Gbps system for a route linking Paris and Frankfurt in late 2009.

"What will be a significant differentiator is the control/ management plane interworking across platforms - the integration of IP MPLS with optical networking products."

Ron Kline, Ovum

Alcatel-Lucent claims to be the first vendor to offer a 100Gbps system using a single carrier.  Ciena/Nortel’s current offering is an extension of its 40Gbps coherent system and uses two 50Gbps sub-carriers that fit into a 50GHz channel.

But analysts downplay the significance of the advent of a 100Gbps single-carrier system. “Technology leads are short-lived,” says Ron Kline, principal analyst, network infrastructure at Ovum. "I’m not sure if there is a preference between single- versus dual-carrier from service providers either.”

What will be a significant differentiator, says Kline, is the control/ management plane interworking across platforms - the integration of IP MPLS with optical networking products. “Alcatel-Lucent is one of the few vendors which do both well and may have an edge pulling it off,” he says.

Ovum’s Dana Cooperson thinks it is significant that, like Ciena, and unlike some others, Alcatel-Lucent is also doing 40Gbps coherent. “I’ve heard some folks say they think 40 Gig coherent isn’t going anywhere, but the reasoning hasn’t made sense to me,” says Cooperson, Ovum’s vice president, network infrastructure. “If you have bad fibre, which loads of carriers do, and you want a mixed channel capability, which all carriers do, you’ll expect to get both in the same product.”

What’s been done?

Alcatel-Lucent’s 100Gbps system implements polarisation multiplexing quadrature phase-shift keying (PM-QPSK) modulation with coherent detection. The coherent receiver is based on an in-house application specific integrated circuit (ASIC) that includes high-speed analogue-to-digital (a/d) converters and a digital signal processor (DSP).

Alcatel-Lucent would not say if the ASIC uses a 60nm or 45nm CMOS process or what the sampling rate of its a/d converters are but it did say that it has built-in sufficient headroom to operate at a 64Gsamples-per-second rate. The system also uses hard-decision forward error correction (FEC) but, according to Sam Bucci, vice president, terrestrial portfolio management at Alcatel-Lucent, it is looking at a soft decision FEC scheme for a future version “that is not too far away”.

Additional system performance characteristics, according to Bucci, include the ability for the lightpath to travel through as many as 20 reconfigurable optical add/drop multiplexers (ROADMs) before needing optical-electrical-optical (OEO) conversion. The system also has a tolerance of at least 30ps for polarisation mode dispersion and 60,000 ps/nm for chromatic dispersion, says Bucci.

For 40Gbps coherent transmission, Alcatel-Lucent is using polarisation multiplexing binary phase-shift keying (PM-BPSK). Since less information is encoded on the symbol streams, this is a more demanding implementation because the implementation operates at 20Gbaud-per-second rather than the 10Gbaud-per-second of 40Gbps PM-QPSK coherent systems.“We were looking for a solution that was applicable not just for terrestrial but for submarine,” says Bucci. “Therefore the reach we were looking to achieve was greater than perhaps could be accomplished by other modulation formats.”

Alcatel-Lucent says PM-BPSK is also better able to withstand non-linear effects such as cross-phase modulation.

Is Alcatel-Lucent open to adopting an ASIC from a third-party developer for its future 100Gbps systems? “It would be irresponsible of any system vendor to overlook a solution that can bring a cost advantage to their customer,” says Bucci. “If there is a solution that can fit into the scheme we have developed, then yes, we would have to consider it if it produces an economic advantage.” Such an 'economic advantage' would have to be significantly more than just a 10 percent cost-saving, he says.

Volume production of the 100Gbps system will begin at the end of June 2010. Two client-side interface boards are available: a 10x10Gbps and a 100Gbps native port using a pluggable CFP transceiver.