Like waves breaking on shore, technology often comes in sets. One breakthrough leads to a set of innovations and related changes. In optical networking, coherent detection was a big wave that led to massive changes in system capacity and reach. It allowed for overcoming fiber imperfections, the use of complex modulation techniques and enabled software control previously impossible. System and component vendors developed generations of DSP devices in step with photonic component advances that brought further huge increases in system capacity while also decreasing physical size, power consumption and per bit cost. The past ten years have been remarkable.
But what now? What will the next ten years bring?
Nokia and R&E networks
Long a proving ground for networking technology, Research & education networks continue to push the bounds of optical networks. Many R&E networks were the first to trial technologies such as IPv6, 100G core routing and coherent optical detection, well before mainstream communication service providers put these components into production networks. Nokia Bell Labs research contributed greatly to the evolution of these technologies into systems, now deployed by all type of network operators, including global NRENs.
One example is Nokia’s Photonic Service Engine (PSE) and its use of probabilistic constellation shaping (PCS) to maximize capacity over any distance and on any fiber span. A concept pioneered by Nokia Bell Labs, PCS pushes optical performance towards the Shannon limit, the maximum possible information transfer rate.
Practical networks require a range of transmission capabilities. Some need the maximum capacity possible over a given span. Others require the farthest reach possible, often at lower transmission rates. Meeting these requirements often means engineering optical links using different costly transponders.
Recent field results
PCS uses constellation points with high amplitude less frequently than those with lesser amplitude to transmit signals that are, on average, more resilient to noise and other impairments. This enables tailoring the transmission rate to each optical channel, delivering up to 30% greater reach while significantly improving spectral efficiency. This technology allows networks to attain maximum capacity over practical, real-life optical spans with fewer different equipment components. Several networks have proven PCS in recent trials. These trials utilized Nokia PSE based optical systems to support short, medium and long haul, subsea optical spans at very high capacity.
In 2019, M-net trialed PCS, allowing them to exceed 500Gbps over existing optical spans, maximizing the capacity of their network. In a Bavarian span route from Munich to Regensburg with an ILA site at Standort, the trial covered 320Km with span-optimized 500Gb wavelengths. M-net expects this type of performance provides them with backbone capacity to meet growing demands from video applications and emerging 5G networks.
Telecom Italia (TIM) achieved a European optical network speed record in May of 2019 in a trial using PCS enabled equipment in a 350 Km span between Rome and Florence. The trial used PSE-3 powered equipment on the 1830 PSS platform, achieving a speed of 550Gbps. As part of the same trial, TIM reached transmission rates of 400Gbps over 900Km between Rome and Milan and 300Gbps over 1750Km. These tests complement TIM’s existing Nokia 1830 PSS powered DWDM network covering over 16,000Km of fiber, touching 65 PoPs throughout Italy.
Similar trials on Netia’s production network in Poland demonstrated the ability to maximize span reach and capacity with the 600Gbps-capable PSE-3. Netia is the largest alternative network operator in Poland, spanning 50000kms of fiber connecting over 80% of the major office buildings in the country.
The Netia trials proved operation over existing live short, medium and long-haul networks without re-engineering. Tests proved operation at 500Gbps in metro (15 & 40Km), 450Gbps in regional (300Km) and 400Gbps in long haul (600Km) networks.
In early 2020, Angola Cables tested the PCS enabled optical transport in a span between North America and Africa, using the MONET and SACS undersea cables. In this trial, the Nokia 1830 PSI-M using PSE-3 equipped transponders linked Miami, Florida to Sangano, Angola with an amplifier site in Fortaleza, Brazil. This 12,635Km non-regenerated span operated two wavelengths at 300Gbps.
This test showed how a simple subsea terminal can be formed with PCS powered transponders and related ROADM components. This solution offers high capacity and extended reach with relative equipment simplicity. For the operator, they can offer high capacity, low latency service between North America and South Africa.
The next wave
PCS is but one innovation available to help R&E networks push existing boundaries. Nokia’s unique technology set extends through optical transport to layer 2 and 3 switching and routing. Combining OTN switching, GMPLS control plane, CDC-F ROADM, layer 2 switching and powerful IP/MPLS routing into a family of solutions, NRENs can deliver a wide set of resilient services to their institutional network users.
Increased capacity and reach will continue as needed goals for all networks. But as we move into the new decade more is needed. The next wave in optical networking may be about flexibility, fiber utilization and system openness rather than headline capacity. 800Gbps isn’t required on all spans but what appears more relevant is capacity at reach and cost per bit; performance with simplicity.
The next wave of optical networking technology utilizes advanced coherent DSPs, silicon photonics and novel component packaging- all combined to optimize system capacity, reach and cost. These innovations focus investments on practical network pain points, roughly 400Gbps at any optical span distance and roughly 300Gbps at ULH or subsea distances. While higher capacities, such as 800 Gbps are
certainly demonstrable, factors such as cost, power consumption and interoperability with existing line systems makes their practicality questionable. We believe that 400Gbps will dominate applications from short, single spans through long haul for some time.
For these reasons, Nokia’s WaveFabric optical components and systems have focused development on optimizing 400G capacities. Our 5th generation PSE is an application optimized coherent DSP with two variants: PSE-Vc, a metro-regional chip operating at 64 Gigabaud between 100G and 400G and PSE-Vs, a long haul processor operating at 90 Gigabaud between 200G and at least 600G.
Building on Nokia’s probabilistic constellation shaping algorithm, these PSE innovations deliver another 60% improvement in optical reach and a 15% improvement in spectral efficiency while requiring 40% less power. These innovations will continue to be built into evolving network hardware that helps NRENs deliver high capacity, where it’s needed: your member institutions.
Latest DSP generation: https://www.nokia.com/networks/technologies/pse-super-coherent-technology/
Webinar on Nokia and R&E networks: https://connect.geant.org/2020/02/24/webinar-nokia-and-re-networks-04-march-2020-2