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Cable bites back

(Image credit: Image Credit: Asharkyu / Shutterstock)

Fibre to the Home or Building is now a very popular choice for new housing developments and business parks across the globe. Extending broadband availability and raising public expectations provides a major boost for the industry, but there is a greater challenge in regions with a well-established copper or cable infrastructure. Telcos are already stretching DSL technology to discourage customer churn. Cable too has significant territory to defend: it begins with a more powerful offering, but MSOs cannot be complacent. QoS is the new battle cry, and Distributed Access Architecture (DAA) offers a major challenge to the spread of Fibre to the Home. The migration to DAA is inevitable, but not to be undertaken lightly, says Jon Baldry Metro Marketing Director at Infinera. 

The global advance of FTTH has been dramatic, and it is expected to provide nearly 50% of all broadband subscriptions by 2022. But it is worth noting that this has been driven by exceptional uptake in certain countries, notably the Far East, where the legacy copper and cable infrastructure was less established. China accounts for over a third of the global broadband total, and over 70% of those connections are on FTTH. Singapore has 95% FTTH, South Korea over 80% and Hong Kong over 70% according to the Fibre Broadband Association. 

Compare that with Europe, with its legacy copper and cable infrastructure, where FTTH penetration is barely 10%. Fibre still has a long way to go, and installation will take time in the old world with its stricter planning regulations and narrow old-town streets.

The call for QoS

What does the world want from broadband? Expectations are changing rapidly. The original Internet demand was for access to information, with an emphasis on download speed, and ADSL addressed this demand very successfully with its asymmetric service. However, fibre now delivers about six times the capacity that DSL can manage.

There is still huge demand for downloads and streaming video and services like 4K HDTV are pushing demand way beyond the capabilities of current DSL technology. More significantly, in addition to the video demands, users also use a broad range of services such as social media, gaming and potentially, in the not too distant future, virtual or augmented reality where upload speeds and latency become much more important. Here legacy cable delivery does have a distinct disadvantage – although it has accelerated its download speeds to stay around 80% of fibre capacity, cable’s upload speeds are more like one third of what FTTH can offer.

Cable was in a strong position in the days of asymmetric Internet usage, but today’s soaring demand for massive bandwidth, fast uploads, low latency and high reliability presents a serious challenge, and the industry is looking to a new Distributed Access Architecture (DAA) to meet this challenge. This is a radical move that will impact the entire system for cable multiple service operators’ (MSOs) optical networks, from “fiber-deep” access networks to support Remote PHY Devices (RPDs) to the need for enormous bandwidth scalability throughout their entire networks.

The DAA response

For a couple of decades cable operators have used Hybrid Fibre Coax (HFC) to connect the core to the access networks. The fibre carries the data as analogue radio frequency (RF) signals, similar to those in the coaxial access cables, rather than digital packets as in a typical fibre network like FTTH (Fig 1). This analogue infrastructure is expensive to operate and maintain. 

Digital signals are more tolerant of signal to noise degradation and are therefore less affected by attenuation, whereas analogue signals need a chain of power hungry amplifiers along the route to maintain signal strength and quality. This analogue technology was designed to suit earlier network requirements, which it supported well, but it cannot scale to meet today’s increasing demands. 

Figure 1: The Current HFC Access Network 

Figure 1: The Current HFC Access Network 

Note also that each Optical Network Terminal (ONT) typically serves several hundred homes, requiring costly analogue equipment that requires considerable maintenance. With so many subscribers per node, the system struggles to support bursts in demand, slowing down delivery at those most critical times. 

The new “fibre deep” approach pushes today’s default packet-based digital fibre technology out closer to the end point (Fig 2). Replacing analogue channels and the older transmission protocol also frees up spectrum in the remaining shorter coaxial plant for more efficient use of capacity, enabling Full Duplex delivery so that upload speeds will be able to match download speeds. This narrows that gap between FTTH and Cable for interactive gaming, virtual reality and social media purposes – as well as increasing its potential for future Internet of Things (IoT) applications where masses of data may be uploaded from countless small devices.

Note also in Fig 2 that increasing in the number of nodes closer to the end users means that each one serves around one tenth of the number of subscribers, and this facilitates exceptional interactive services. The cable network has for many years supported on-demand content, and the updated network architecture makes room for more locally stored content. Being closer improves responsiveness and Quality of Service (QoS), especially during peak hours. 

These developments will present a serious challenge to the arrival of FTTH providers, who already have to compete against an existing infrastructure and established customer base.

Figure 2: HFC to Distributed Access Architecture (DAA) 

Figure 2: HFC to Distributed Access Architecture (DAA) 

Huge potential versus tricky demands

DAA offers exciting opportunities, but migration to this new architecture presents a raft of new challenges. Fibre and DWDM pushing deeper into the access network from the secondary hub to remote RPDs means a tenfold or so increase in the number of end points for the DWDM network. Secondary hubs will now also have to aggregate 100s of 10Gb/s circuits from RPDs into efficiently filled 100Gb/s backhaul circuits to the primary hubs. These secondary hub locations are often already space and power constrained and when they aren’t, operators may look to consolidate secondary hubs, creating a space and power constrained environment.  

Selecting suitable equipment will no longer be a simple matter of asking a preferred supplier to meet the required performance levels, it will be necessary to look closely at the specifications to see if devices are sufficiently compact and power efficient to optimise scarce secondary hub real estate and to provide additional capabilities that can address the significant operational challenges of managing such a high density aggregation. With a tenfold or so increase in the number of RPDs terminating the DWDM network, installation and operating expenses will soar unless care is taken to choose the most compact, reliable and easy to maintain equipment. 

Optical equipment suppliers are aware of these concerns and are rising to the challenge of mass deployment of DAA networks. Great advancements are being made in terms for density, power consumption and addressing the operational challenges of managing potentially 1000s of fibers within a secondary hub rack. What’s more, the industry has been working to bring the International Telecommunications Union’s (ITU) vision of autotuneable WDM-PON optics up to the performance levels required to support the reach and capacity requirements of DAA networks. This eases the pressures of commissioning and maintaining extensive DWDM optical networks by replacing the technicians’ burden of determining and adjusting wavelengths at every installation. Autotuneable technology will automatically select the correct wavelength without any configuration by the remote field engineer enabling them to treat DWDM installations with the same simplicity as grey optics. 

These are the sort of challenges that will be faced as MSOs migrate to DAA, and they will need to take a very close look at their choice of equipment and solutions in order to meet the very specific challenges of fibre-deep access networks. However, a successful DAA rollout is not just about what happens in the access network. DAA will also create a surge in bandwidth demand throughout the entire infrastructure – from access through transport to core. Unless steps are taken to reinforce, optimise and automate the entire network capability, the most powerful, responsive and efficient access network could become its own worst enemy.


Already nearly a half of all US consumers are using streaming video services and 70% “binge watch” TV series, while virtual and enhanced reality services and 4K high definition TV are still poised to go mainstream. So future-proofing a cable MSO’s network means preparing for a highly uncertain future. 

Operators will need help from specialist optical equipment providers to optimise optical transport platforms to their specific needs, creating network architectures that will be highly scalable, that simplify operations, accelerate the launch of new services, and minimise total cost of ownership. Something that will only be achieved by installing intelligent networks that integrate best-in-class technology and automate a significant proportion of manual operations.  

Jon Baldry, Director Metro Marketing at Infinera    

Image Credit: Asharkyu / Shutterstock

Jon Baldry
As Director of Infinera’s Metro Business Unit, Jon has responsibility for Strategic and Technical Marketing for the company’s metro portfolio. Jon has spent over 20 years working in the telecoms industry, primarily in optical and packet-optical systems. He joined Infinera through the acquisition of Transmode in 2015, having joined Transmode in 2004 and has previously worked for Lucent Technologies and Sycamore Networks in a variety of engineering, sales and marketing roles. Jon is a Chartered Engineer and holds a Bachelor of Engineering.