ADVA runs the rule over its TeraFlex platform

Gazettabyte talks to Jörg-Peter Elbers about the recent trial of ADVA’s FSP 3000 TeraFlex platform in Tele2’s network and gets his views on industry trends.

Herzliya marina. Source: Gazettabyte

It is early morning and the air is cool. I'm seated outside at a coffee bar in Herzliya’s marina awaiting Jörg-Peter Elbers, senior vice president, advanced technology, who is in Israel visiting local ADVA staff.   

He arrives as the bar opens and we are the only customers.

Just as we are about to start, the waitress informs us that the barista has yet to arrive. Breakfast can be ordered but we must wait for coffee. 

Flexing the TeraFlex 

ADVA trialled its TeraFlex platform on a Tele2 route between Tallinn and Frankfurt. 

First detailed in 2017, the TeraFlex is a one-rack-unit (1RU) stackable chassis that supports three hot-pluggable 1.2-terabit modules or ‘sleds’. Each sled uses an Acacia AC1200 coherent module that supports two line-side wavelengths, each capable of coherent transmission at up to 600 gigabits-per-second (Gbps).

The TeraFlex was designed to address the needs of large-scale data centre operators that want power-efficient, high-capacity and compact platforms. But interest in the platform has broadened to include telcos and research and educational network operators. 

Jörg-Peter Elbers

For the trial, the transmission distance was increased by using loopbacks at the route’s locations. From an operational perspective, it means equipment is needed at one site only. The network also features reconfigurable optical add-drop multiplexers (ROADMs) at all the intermediate sites.    

Data was sent in 100-gigabit increments over a spectral slice. A spectral slice is a relatively new concept whereby an operator leases a portion of the unused spectrum on a fibre to interested third parties.  

The optical performance achieved includes sending a 500-gigabit optical signal over 1,016km and a 200-gigabit signal over 5,738km.

ADVA used network telemetry data gathered by the TeraFlex to boost overall optical performance. “That was also an intention of the trial: how hard can we drive the system and what is the top-line performance we can get,” says Elbers.

The TeraFlex has also been trialled by Telecom Italia in its backbone network. A 600Gbps wavelength was sent over a distance of 100km on an optical route designed for 10Gbps while a 300Gbps signal was sent over a distance of 2,500km.

Differentiation

ADVA dismisses the notion that TeraFlex’s optical performance is dictated solely by Acacia’s AC1200 module such that the scope for platform differentiation is limited when compared with competitors’ designs that also use the Acacia module. 

“The TeraFlex does use certain hardware but there is a tremendous amount of configuration flexibility, literally thousands of configurations you can use,” says Elbers. 

These include different modulation formats and whether fractional quadrature amplitude modulation (QAM) is used. Fractional QAM is a feature of Acacia’s coherent module whereby two adjacent modulation formats, for example, 8-QAM and 16-QAM, are each used for a percentage of the transmission time to fine-tune the data rate. The baud rate for a given data rate can also be altered to adapt the spectrum used for the transmission.  

For the trial, a QPSK reference signal was first sent, a signal that will go the furthest. Based on the performance achieved, a decision is made as to whether the data rate transmission performance can be bumped up, says Elbers.  

Networks are run conservatively, he says. At the start of a link’s life, the large safety margin built-in can be exploited to cram more data across a link.  

“I might run into issues at the end of the life of the system but I can drive the system harder at the beginning,” says Elbers. “The result is more capacity from the start and better economics.”

Elbers says that optimising the network, even at its end-of-life stage, by exploiting the capacity available in each slot and optimising the spacing and data rate, a 30 percent capacity improvement can be achieved compared to a non-optimised network. 

But the bigger potential is if the operator is willing to operate the line system using lower margins, adjusting as required over its operational life, whereby a doubling of capacity is possible.  

Silicon photonics democratises component development and we have activities in that area involving coherent engines and optics and we see the potential there 

600G versus 800G

Elbers says that there is a market perception of a 600 gigabit-class of coherent performance and an 800 gigabit-class. Systems vendors Ciena and Infinera have announced solutions that deliver 800 gigabits per wavelength. 

But such solutions do not yet exist, he says, adding that operating at a lower symbol rate per wavelength results in a lower implementation penalty. “Components are imperfect compared to the theoretical performance and the closer you stay with the maturity curve of the technology, the lower the delta is,” says Elbers. “With 60 gigabaud [GBd] and QPSK modulation, you are very close – sub 1 decibel - from the theoretical performance; that is what we can get.”

ADVA also points out that a TeraFlex sled can deliver 1.2 terabits using two optical wavelengths and a single coherent DSP.  

For the Tele2 trial, the TeraFlex also delivered 800 gigabits of data using a 125GHz-wide channel. “This was a superchannel configuration,” says Elbers.

The AC1200 can operate close to 70GBd while Infinera’s ICE6 will operate at 88GBd using sub-carriers while Ciena’s WaveLogic 5 can operate at up to 95GBd. 

“There are certain technology evolution steps; 95GBd appears a half step,” he says. The industry has gone from thirty-something to sixty-something gigabaud and now the aim is to double it again. Elbers believes 120GBd and even 140GBd will be possible. 

“It is not just the building blocks but integration which will form more and more a key part,” says Elbers. “Bringing everything as close together as possible.” This is needed to tackle the ever-increasing challenge of radio frequency (RF) design as the symbol rate continues to rise.

Acacia’s acquisition 

When Cisco announced in July its intention to acquire Acacia, ADVA commented that such developments are to be expected as networks become more open and disaggregated. 

ADVA also pointed out that Cisco intends to run Acacia as a component business unit and will continue to sell to all equipment makers while Ciena’s Optical Microsystems unit is making its WaveLogic coherent DSPs and module technologies available to the wider market. And with companies such as NEL and Inphi, merchant DSP experts will continue supplying the market.

While not going into detail, Elbers points out that it is common practice to have clauses in contracts that ensure continuity of supply under such circumstances. He also adds that designing in another coherent DSP into a platform such as the TeraFlex is “a big decision” but that the TeraFlex has been architected with such modularity in mind.

Vertical integration

ADVA has a team that addresses the company’s technology needs to help the company decide whether to make or buy. “What areas makes sense for us to do on our own and which areas does it make sense to just buy from a merchant vendor,” says Elbers. 

The company has always designed its optical amplifier solutions and developed its MicroMux solution that allows low-rate client signal interfaces to interface efficiently to the high-capacity TeraFlex.

Only a few companies will continue to make their own coherent DSPs, he says, especially as next-generation designs move to the costly 5nm CMOS process.    

Silicon photonics design expertise is another skill ADVA has. “Silicon photonics democratises component development and we have activities in that area involving coherent engines and optics and we see the potential there,” says Elbers.  

Our interview ends and we make our way to a taxi rank beyond the marina so that Elbers can travel to Ra’anana where one of ADVA’s two local offices is located. 

We find a driver before realising he is not first in the rank. The cab driver that is first in the rank strides towards us and a heated discussion between the drivers ensues. Agreement is reached and we move to the first cab but not before Elber’s new driver restarts the argument. Eventually, Elbers sets off for the rest of his day.

The morning air has heated up.