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Has cable finally found a catalyst for DAA?

(Image credit: Image Credit: Atm2003 / Shutterstock)

No event in human history has done more to demonstrate the importance of internet connectivity than the current Covid-19 pandemic. Though social distancing and physical separation have become the norm, people still need to connect, communicate, and collaborate. With so many people now working from home, broadband access has taken on increased importance and relevance.

In 2018, when one of my colleagues wrote an article about the transformation of cable’s hybrid fibre coax (HFC) networks to a distributed access architecture (DAA), expectations were high that we would see a rapid global transition toward a fibre deep DAA cable network.  However, in the subsequent two years, that massive shift has not occurred, and according to Omdia’s 2020-2025 Cable Broadband Access Equipment Forecast, only about 6 per cent of global cable broadband access equipment in 2019 was for DAA transition.  However, following another flat DAA investment year in 2020, Omdia predicts significant adoption, with 34 per cent of equipment sales supporting the DAA transition by 2025. 

Today and tomorrow

On average, the path to an HFC-connected home or business is approximately 75 per cent fibre and 25 per cent coax today. Only in the immediate vicinity of a connected customer is the network composed of coax, with each coax network segment connecting ~300 homes. Fibre is run to a neighbourhood termination point (called a fibre node) where connectivity continues via a tree-and-branch coaxial network. So, in a typical large metro area, a cable operator will have fibres terminating in thousands of neighbourhoods.  In order to increase performance and capacity per home, operators continue to drive fibre deeper into each service area and shrink the number of customers per fibre node.

In the existing network architecture, digital signals are modulated and carried over fibre on analogue waveforms. The primary role of the fibre node is to convert the analogue optical signals to electrical for coaxial transmission. But with DAA, we replace the analogue fibre transmission in the outside plant with digital optical transmission (like other parts of the telecommunications network) and only launch the analogue waveforms at the fibre node over the coax. This turns out to be a profound change that enhances signal transmission quality and reliability, and enables a path to 10G connectivity for enterprise and business customers.  It also turns out to be a significant operational shift for cable operators.

10G and multi-service delivery

By locating the unique analogue aspects of coaxial transmission deeper in the network – to the fibre node – cable operators are creating a digital optical demarcation in the outside plant.  The fibre node can then be modularised to support incremental services beyond 10G high-speed internet connectivity.  One example is connectivity for neighbourhood 5G small cell sites.  With digital optical connectivity at the fibre node, one could envision a series of low-power small cells at each fibre node providing enhanced coverage and offloading in-home 5G/4G mobile traffic.  With more than 75 billion wireless Internet of Things (IoT)-connected devices projected in a few years, one can also envision neighborhood small cells enabling mass IoT connectivity for everything ranging from environmental sensors to smart utility meters and neighborhood security feeds.

How do we make it happen?

While the anticipated adoption of DAA cable networks has not yet achieved mass commercial deployment, what have we learned from early trials and deployments and how might we apply these learnings to accelerate the pace of DAA migration going forward?  We believe at least part of the answer lies in automating, innovating, and disaggregating.

Automating installations

First, we must address the real operational impacts from changes in the DAA network.  A digital optical fibre node for DAA can provide optical to coaxial conversion for multiple neighbourhoods or serving areas, with each serving area fed by ~10G connectivity from the hub site.  Since the fibre node will typically only be fed by a single fibre pair, we must either utilise multiple 10 Gb/s optical wavelength-division multiplexed (WDM) signals (one per coax serving area) or multiplex/demultiplex multiple 10G signals into a higher-capacity 100G/200G signal for transmission to/from the fibre node.  Multiplexing/demultiplexing can add additional cost and complexity to the network as we need to install an electrical switch or transponder at each end of the fibre to transmit/receive the converged 100G/200G signal and break it into individual 10G streams on the other end.  Alternatively, if we utilise 10 Gb/s DWDM pluggable optics, we either have to program the optic for the right wavelength every time we do an installation or we need to provide outside plant personnel with a collection of fixed-wavelength pluggable optics – one per DWDM wavelength utilised.  We are left with the choice of either increased CapEx or OpEx, or both.

Fortunately, there is a better way.  With Auto-tuneable 10G DWDM pluggable optics, cable operators can deliver N x 10 Gb/s wavelengths to the fibre node while minimising capital and operational costs.  Auto-tuneable optics utilise a passive filter to let a single wavelength pass, and an Infinera-patented two-way handshaking algorithm is embedded in the pluggable optic to auto-negotiate and lock onto the correct wavelength within one to three minutes. Outside plant personnel can utilise a single 10G SFP+ pluggable optic to deliver DWDM support for up to 80 wavelengths per fibre node. Gone is the need to carry a host of fixed-wavelength pluggable optics (one per wavelength) or to program the pluggable optic during every new installation and coordinate with headend personnel to ensure far-end reception.  Auto-tuneable DWDM pluggable optics are a great way for cable operators to reduce CapEx, shorten installation times, and eliminate configuration errors.

Innovating beyond DAA

Beyond Auto-tuneable optics, XR optics is the next major inflection in optical transceiver technologies. XR optics utilises digital signal processing (DSP) to subdivide the transmission and reception of a given wavelength into a series of smaller frequency channels called digital subcarriers. These digital subcarriers can be independently modulated, managed, and assigned to different destinations, enabling the industry’s first scalable point-to-multipoint, direct low-speed to high-speed optical transceiver connectivity.

A single 400G XR optics hub module generates 16 x 25 Gb/s digital subcarriers. One or multiple digital subcarriers can be assigned to a specific destination to provide the required bandwidth. XR optics transceivers are designed to be installed into a wide range of networking equipment including Ethernet switches, routers, and headend aggregation systems. XR optics can provide connectivity up to 1,000 km and is targeted for industry-standard pluggable form factors like QSFP-28, CFP2-DCO, and QSFP-DD.  With XR optics, one can envision installing a 400G transceiver at a headend location to optically express traffic in 25G assignable increments all the way to multiple fibre node locations – bypassing or eliminating intermediate routers/switches. By reducing the number of optical transceivers in the network and simplifying or eliminating intermediate aggregation, XR optics economic modelling on real-world networks has demonstrated multi-year total cost of ownership (CapEx and OpEx) savings in excess of 70 per cent.  While still under development, with anticipated delivery in 2021, XR optics offer the potential to help cable operators simplify their networks and better utilise their capital to accelerate the pace of cable network transformation.

Disaggregated routing

With networks evolving rapidly and fibre nodes taking on a more prominent role in the cable network as multi-service optical demarcation points, service providers of all types, including cable operators, are having a difficult time modelling future traffic demand.  With a multi-slot chassis-based solution, there is always fear of buying too much capacity and stranding precious working capital or buying too little and impacting service delivery.  That is part of the reason you see a movement toward disaggregated routing solutions, where a family of pissa-box routing/switching elements can be deployed like Lego bricks in configurations including standalone, multi-unit stacked, or a horizontally scalable router configuration with a virtual backplane.  In addition, some vendors are enabling their routing software to run on a broad range of merchant silicon and hardware, including that from white box suppliers. With open disaggregated routing, cable operators increase their flexibility and future hardware options while better aligning real capacity demands to network infrastructure costs.


The Covid-19 pandemic has further reinforced the importance of our broadband networks – for entertainment, work, and human connectedness.  To date, cable’s transformation toward a DAA network that provides a path to 10G connectivity and support for multiple services, including 5G wireless small cells, has not seen mass commercial deployment.  However, by automating and simplifying operations with Auto-tuneable optics, further simplifying and cost-reducing the network with innovative point-to-multipoint XR optics, and reimagining network routing with open and disaggregated solutions to better align capacity demand to networking costs, cable operators may just find that they can accelerate their DAA transformation and bring the network of the future to life sooner than expected.

Tim Doiron, Sr. Director Solution Marketing, Infinera
Jay Rolls, Technology Consultant & Cable Executive,
Charter Communications