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Coherent Point-to-Multipoint Pluggable Optics to the Rescue

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September 30, 2021
By Fady Masoud
Director, Solutions Marketing

Reflections from Light Reading’s 400G, 800G Pluggable Digital Symposium

I recently had the privilege of participating in the first session of Light Reading’s Optical Networking Digital Symposium, a webinar on “400G and 800G Pluggable Optics and IPoDWDM for Telecom.” This was followed by a panel discussion on the status of coherent pluggables and some forward-looking views on the next generation, such as 800G coherent pluggables.

I love having service providers on these events, as they share their day-to-day experiences and bring up very valuable insights.  There were three key points I took away from both sessions. Vivek Gaur from Colt Technology Services reiterated the importance of embracing open line systems and 400G coherent pluggables.  Buddy Bayer, Chief Network Officer at Windstream, sees point-to-multipoint solutions, such as XR optics, in the access or at the edge of the network, while Paul Choiseul, CTO EMEA and Latin America at American Tower, spoke about the impressive results of trialing XR optics over an existing PON network.

Astronomical Orders of Magnitude!

My topics focused on the need to extend coherent technology toward the access edge of the network as capacity demands continue unabated, with traffic doubling every two to three years. This was echoed by the latest report from ACG Research, which anticipates ~45% annual growth in residential access and metro aggregation1.

More specifically, 5G is putting an unprecedented level of pressure on the network: between 10 and 100 times more capacity is expected2 from the network, with 25 times lower latency and 10 times more connected devices per square kilometer (km2).

In my 25 years in the telecom industry, I have never seen a service provider that could scale their space and power by those astronomical orders of magnitude. Furthermore, cloud applications and 5G require multi-access edge compute (MEC) sites located as close to the end user as is economically feasible to reduce latency, accelerate performance, and reduce transport costs.

In addition, this compute function is becoming distributed across the edge of the network, it is increasingly challenging to find the space, power, connectivity, and capital budget necessary to achieve such deployments.  Not an easy task, is it?

It is becoming clear that network operators are exploring innovative ways to scale while leveraging existing network assets and rearchitecting the network to cope with connectivity challenges triggered by cloud, 5G, and MEC.

On The Lookout for Innovative Solutions

The significant misalignment in metro aggregation networks – between point-to-multipoint network traffic patterns and the point-to-point technology used to transport that traffic – limits network operators from scaling the network efficiently and cost-effectively. The need for twice as many transceivers as endpoints and numerous intermediate aggregation sites increases complexity and operating costs as demand for higher capacity and the number of connected devices continue to grow in the network.

The good news is that the latest innovations in digital signal processor (DSP) design and feature miniaturization now allow coherent pluggables to do more than just point-to-point connection. Building a state-of-the-art DSP and opto-electronics and combining that with the know-how needed to adapt system-level features into a pluggable form factor allows coherent pluggables to be equipped and operated in a wide range of platforms, as well as in different traffic patterns: point-to-point, point-to-multipoint, and breakout (4 x 100G).

Laying Down the Right Foundation

As network evolution often takes place in phases, it makes business and operational sense to deploy XR optics for today’s point-to-point connections, because XR optics lays the foundation for an architecture that can evolve to overcome ongoing challenges like increasing capacity, flexibility, and service agility. Then, when service providers are ready to leverage the point-to-multipoint capabilities of XR optics, it can be done in easily and seamlessly as the building blocks, or the digital subcarriers, are already in place.

XR optics’ support for point-to-multipoint reduces the number of transceivers by more than 50%, which translates to significant CapEx and OpEx savings. In addition, the same digital subcarriers that were used in that point-to-point connection between the hub and the aggregation site can now be assigned to different destinations. What used to be the aggregation point in the network can now be pushed to the hub, thus eliminating most – if not all – intermediate aggregation sites and replacing them with a single passive splitter/combiner device, as depicted in Figure 1. This is a great example of leveraging existing infrastructure to scale and dramatically reduce CapEx/OpEx while significantly simplifying the network architecture. The “coherent” aspect of XR optics enables a more scalable infrastructure, where service providers can turn up way more capacity on existing fiber – an order of magnitude higher than current access technology.

Coherent-Point-to-Multipoint-Pluggable-Optics-to-the-RescueFigure 1: Simplifying the network with XR optics point-to-multipoint architecture

Another point I wanted to bring up to the audience is how this capacity is assigned and allocated in the network. XR optics enables software-programmable bandwidth, where one or many digital subcarriers can be assigned to any endpoint that requires more bandwidth, hence matching allocated capacity to real traffic demand. This prevents overengineering the network with excessive capacity and the CapEx associated with it. In addition to being remotely provisioned without truck rolls, capacity can be shifted across the different endpoints based on actual demand, the time of day, the time of the year, etc. In return, XR optics’ dynamic capacity allocation translates into a positive impact on operations and service velocity.

Things Are About to Change

I don’t want to sound too old (I am not!), but for the longest time, upgrading the capacity of a specific site triggered the upgrade of the entire network – a node upgrade effectively equaled a network-wide upgrade. It’s rare that one generation of an optical engine “talks” directly to the previous generation. XR optics supports intergenerational interoperability thanks to the fact that all the modules at the hub, endpoints, and even between the different generations (e.g., 800G XR) all have 25G subcarriers as building blocks. Intergenerational interoperability enables services providers to scale at their own pace while reducing operating expenses, leveraging existing assets, and maximizing ROI. The benefits of XR optics are summarized in Figure 2.

Coherent-Point-to-Multipoint-Pluggable-Optics-to-the-RescueFigure 2: Benefits of XR Optics

Another attribute of XR optics that is particularly key when more endpoints are added to the network is its great fan-out. As many 100G XR optics at various endpoints can be connected to a single 400G XR at the hub in a point-to-multipoint configuration, this greater fan-out (400G → N x 100G) enables service providers to aggregate higher-capacity traffic from a larger number of sites.

As highlighted in a recent blog post from my colleague, Jon Baldry, the journey to extend DWDM and coherent technology to the edge can start with Auto-Lambda, enabling service providers to have an early taste of the benefits of the plug-and-play concept for the non-coherent 10G/25G domain before cranking up capacity in 25G increments with XR optics.

XR optics is currently being trialed by numerous service providers across the globe while the members of the Open XR Forum are busy defining its operational aspects, such as host compatibility and management, paving the way for wide deployment of XR optics by a broad spectrum of network operators in a variety of applications.

It was great to participate in this event. The energy and positive market momentum of coherent pluggables is setting the optical networking industry on an exciting path.


1 Directions in Open Optical Network Designs in Service Providers’ Optical Transport Networks, ACG Research, Sep 2021
2 Source: Statistica, SAMSUNG Insights, CITA, WPP, CNN, McKinsey