FEATURE

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Robin Mersh takes a look at how the industry is creating next-generation optical access fit for 5G

With 5G promising enhanced speeds, new services and new revenue-generating opportunities for service providers, the industry is in a race to unleash the 5G era.

The mobile technology will over a new level of bandwidth, capacity, reliability and scalability which will pave the way for a new range of next-generation technologies. These diverse applications, such as HD-video and virtual and augmented reality, are expected to rely heavily on mobile broadband and will require 5G capabilities such as low-latency, and loss and delay variation to ensure they can deliver the enhanced experience that users crave. The technology will also revolutionise the Internet of Things (IoT), providing the scalability and ­ flexibility to support the exponential number of connected devices expected in homes and businesses.

Ultimately, there is no doubt 5G – and the services and devices it will enable – will bring forward a number of new capabilities and opportunities for the telecom industry. Before this happens, however, there are still challenges ahead that need to be overcome.

Strong foundations

For 5G to realise its full potential, there are a number of elements which must be achieved. Arguably, the most notable of these is the backing of a world-class fixed network with ultra-high capacity and speed to provide fronthaul and backhaul for the unprecedented amount of data 5G is expected to generate.

As such – with the industry well-versed in the benefits of fibre – operators are faced with the urgent task of upgrading their current optical access system to deliver the capabilities 5G will require, including up to 1,000 times more bandwidth, 100 times more connected devices, and a maximum of 1ms latency. These new requirements mean key elements of operators’ PON networks will need to be updated – but new infrastructure is a costly undertaking, with many operators still working out new business models in a data, rather than voice, oriented marketplace.

Evolution for the next generation

There is good news, however. While a network update would previously have meant rebuilding from scratch – an Optical Line Terminal (OLT), for example, might have necessitated a remake of the PON chip – applying network virtualisation technologies such as Network Functions Virtualisation (NFV) and Software Defined Networking (SDN) eliminates this expense and accelerates time-to-market.

Standardising this virtualisation of PON networks will establish a vendor-agnostic system and ensure mass deployment of the technologies, which is key to realising agile and flexible next-generation broadband networks and 5G. This is what the Broadband Forum’s PON Abstraction Interface for Time Critical Applications (TCAs) project with NTT aims to do. Launched last year, it aims to standardise the virtualisation of operators’ PON networks, enabling them to cost-effectively upgrade networks to offer 5G fronthaul interfaces and services for business users.

Issues addressed

Within the project, two issues are being addressed from the operator’s point of view. Firstly, operators need to provide sustainable broadband services for residential users on widely deployed fibre access networks. The second aspect is that operators wish to provide a large variety of services on access networks, such as broadband services for business users and mobile fronthaul for 5G. This opens the door to new business opportunities for vendors, as a disaggregated OLT based on the proposal can be applicable to 5G mobile fronthaul by replacing a low-latency Dynamic Bandwidth Allocation (DBA) software.

Achieving the aim

To make time-critical functions flexible, an appropriate so ware API to modify or to extend functions is required and can be achieved by disaggregating algorithms. In addition to this, the interface between the algorithm part and common engine should be specified as common APIs to ensure they are usable among vendors and operators across the industry.

To achieve this, operators must undergo a two-phase so ware upgrade of their network. The first phase defines the functional modules and interfaces to disaggregate a PON function – for example, DBA – that needs time-critical processing. The key elements are algorithm disaggregation and interface. This work addresses the 11 use cases for DBA for service differentiation, which include ONT sleep, protection and Dynamic Wavelength Assignment (DWA) and functional requirements of the APIs for time-critical applications covering low-latency, DBA and ONT sleep. The detailed specifications of the interfaces as commonly usable among vendors and operators’ functional requirements of these API’s will then be addressed within the second phase of the upgrade.

A 5G milestone

Work on the project is being carried out in two phases, with the first phase defining the disaggregation policy and functional requirements of interfaces to disaggregate PON functions which need time-critical processing. The second phase will define the detailed specifications of the interfaces as Application Programming Interface (API) sets.

Since it was launched, the project has already made quick progress and in June, two scenarios were successfully demonstrated. The first showed how a future OLT could be optimised with DBA software to significantly reduce latency to meet the stringent requirements of 5G fronthaul interfaces. This enables dense small cells to be accommodated cost-effectively by TDM-PON. A second DBA so ware can also be applied to OLTs in fibre-to-the-home (FTTH) services that require high bandwidth efficiency.

Next steps

Following the demonstration, we will now look at whether a cooperative interface, which controls the TCAs shown in the demonstration, can be established between the Central Unit in mobile networks and an OLT. This will involve coordination with standards-defining organisations such as 3GPP and CPRI and IEEE.

The work will also address the configuration of sleep parameters of OLTs and Optical Network Terminals (ONTS) to improve energy efficiency, without negatively impacting quality of service (QoS) and quality of experience (QoE). This allows the ONT to send a sleep request to an OLT when it decides to enter sleep mode in consideration of there being no traffic on the network. Once traffic has entered the ONT network, the OLT is programmed to wake up, ensuring there is no buffer or delay.

­The bigger picture

The project is just one way we are preparing fixed networks for the role they will play in delivering 5G. As players in the industry become fixated on expanding their offerings to these new-to-market technologies, the Forum is working to ensure operators and service providers can deliver these new revenue-generating services efficiently and cost-effectively.

Our fibre access network work area, for example, is defining the architecture and technical requirements for PON-based mobile backhaul networks to provide an end-to-end reference architecture for transport services addressing control, user and management traffic in mobile networks.

Work is also ongoing on fixed mobile convergence to develop a coexistence strategy which enables stress-free market-paced migration to new service launches and interworking between home networks and 5G core components. SD-407/420, for example, specifies a 5G Access Gateway Function that adapts fixed access onto the 5G core, as well as considering and specifying several architectural deployment options and the underlying infrastructure sharing aspects. It will also devise strategies and develop specifications to address operator requirements for interworking existing fixed access subscribers and deployed equipment into a 5G core. This work is being carried out in conjunction with 3GPP.

Achieving a network fit for 5G

With the industry-wide collaboration showcased by the Broadband Forum’s projects, we have no doubt that 5G will be a winner, both with operators who will be able to offer new revenue-generating services, and consumers who will be able to access a whole new world of innovative, cutting-edge services.

It is also clear that applying virtualisation to create next-generation fibre networks makes the finish line closer than we think – and standardisation will ensure that once we get there, the entire broadband ecosystem will emerge triumphant, helping us to realise agile and flexible next-generation broadband networks and the delivery of 5G.

Robin Mersh is CEO of the Broadband Forum

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