• Windstream has used Infinera’s latest optical equipment to send an 800-gigabit signal over 730km.

• The operator wants to reduce the cost of sending bits and slash the time taken to fulfil wholesale orders.

Windstream has sent an 800-gigabit optical signal between the US cities of Phoenix and San Diego.

The operator used Infinera’s Groove modular chassis fitted with its latest ICE6 infinite capacity engine for the trial.

Infinera reported in March sending an 800-gigabit signal 950km with another operator but this is the first time a customer, Windstream, is openly discussing a trial and the technology.

Art Nichols

The bulk of Windstream’s traffic is sent using 100-gigabit wavelengths. Moving to 800-gigabit will reduce its optical transport costs.

Windstream will also be able to cram more digital traffic down its fibre. It sends 12 terabits and that could grow to 40 terabits.

Motivation

Windstream provides residential broadband, business and wholesale services in the US.

“We operate a national footprint for wholesale and enterprise services,” says Art Nichols, vice president of architecture and technology at Windstream. “The optical focus is for wholesale and enterprise.”

The communications service provider has 160,000 miles of fibre, 3,700 points-of-presence (PoPs) and operates in 840 cities. “We are continually looking to expand that,” says Nichols. “Picking up new PoPs, on-ramps and landing spots to jump onto the long-haul network.”

If Windstream’s traffic is predominantly at 100-gigabit, it also has 200-gigabit wavelengths and introduced recently 400-gigabit signals. In April Windstream and Infinera trialled Gigabit Ethernet (GbE) client-side services using LR8 modules.

Windstream is interested in adopting 800-gigabit wavelengths to reduce transport costs. “To try to draw as much efficiency as you can, using as few lasers as you can, to push down the cost-per-bit,” says Nichols.

The operator is experiencing traffic growth at a 20-30 per cent compound annual growth rate that is eroding its revenue-per-bit.

Weekly traffic has also jumped a further 20 per cent during the COVID-19 pandemic. Video traffic is the main driver, with peak traffic hours starting earlier in the day and continuing into the evenings.

Sending more data on a wavelength reduces cost-per-bit and improves revenue-per-bit figures.

In addition to sending a 800-gigabit signal over 730km, the operator sent a 700-gigabit signal 1,460km. The two spans are representative of Windstream’s network.

“Eight hundred gigabits is an easier multiple - better to fit two 400GbE clients - but 700 gigabits has tons of applications,” says Nichols. “We are predominantly filling 100-gigabit orders today so being able to multiplex them is advantageous.”

Another reason to embrace the new technology is to fulfill wholesale orders in days not months. “The ability to turn around multi-terabit orders from webscale customers,” says Nichols. “That is increasingly expected of us.”

One reason order fulfilment is faster is that the programming interfaces of the equipment are exposed, allowing Windstream to connect its management software. “We instantiate services in a short turnaround,” says Nichols.

ICE6 technology

Infinera’s ICE6 uses a 1.6-terabit photonics integrated circuit (PIC) and its 7nm CMOS FlexCoherent 6 digital signal processor (DSP). The 1.6 terabits is achieved using two wavelengths, each able to carry up to 800 gigabits of traffic.

The ICE6 uses several techniques to achieve its optical performance. One is Nyquist sub-carriers where data is encoded onto several sub-carriers rather than modulating all the data onto a single carrier.

The benefit of sub-carriers is that high data rates are achieved despite the symbol rate of each sub-carrier being much lower. The lower symbol rate means the optical transmission is more tolerant to non-linear channel impairments. Sub-carriers also have sharper edges so can be squeezed together enabling more data in a given slice of spectrum.

Infinera also applies probabilistic constellation shaping to each sub-carrier, enabling just the right amount of data to be placed on each one.

The FlexCoherent 6 DSP also uses soft-decision forward-error correction (SD-FEC) gain sharing. The chip can redistribute processing to the optical channel that needs it the most.

Some of the strength of the stronger signal can be cashed in to strengthen the weaker one, extending its reach or potentially allowing more bits to be sent by enabling a higher modulation scheme to be used.

Windstream cannot quantify the cost-per-bit advantage using the ICE6. “We don’t have finalised pricing,” says Nichols. But he says the latest coherent technology has significantly better spectral efficiency.

Rob Shore

Spectral efficiency can be increased in two ways, says Rob Shore, Infinera’s senior vice president of marketing.

One is to increase the modulation scheme and the other is to close the link and maintain the high modulation over longer spans. If the link can’t be closed, lowering the modulation scheme is required which reduces the bits carried and the spectral efficiency.

Windstream will be able to increase capacity per fibre by as much as 70 per cent compared to the earlier generation 400-gigabit coherent technology and by as much as 35 per cent compared to 600-gigabit coherent.

A total of 42.4 terabits can be sent over a fibre using 800-gigabit wavelengths, says Shore, but the symbol rate needs to be reduced to 84 gigabaud shortening the overall reach.

Trial learnings

The rate-reach performance of the ICE6 was central to the trial but what Windstream sought to answer was how the ICE6 would perform across its network.

“We paid really close attention to margins and noise isolation as indicators as to how it would work across the network,” says Nichols. “The exciting thing is that it is extremely applicable.”

Windstream is also upbeat about the technology’s optical performance.

“We have a fair amount of information as to what the latest optical engines are capable of,” says Nichols. “This trial gave us a good view of how the ICE6 performs and it turns out it has advantages in terms of rate-reach performance.”

Ciena, Huawei and Infinera all have 800-gigabit coherent technology. Nokia recently unveiled its PSE-V family of coherent devices that does not implement 800-gigabit wavelengths.

Michael Genovese, a financial analyst at MKM Partners, puts the ICE6 on a par with Ciena’s WaveLogic 5 that is already shipping to over 12 customers.

“We expect 800 gigabit to be a large and long cycle," says Genovese in a recent research note. “We think most of the important internet content providers, telcos and subsea consortia will adopt a duel-vendor strategy, benefitting Ciena and Infinera over time.”

Windstream will adopt Infinera’s ICE6 technology in the first half of 2021. First customers to adopt the ICE6 will be the internet content providers later this year.