Comcast’s DOCSIS 4.0 deployment: cable broadband’s ends and means

In Jonathan Swift’s Gulliver’s Travels, the inhabitants of Lilliput are torn apart by a dispute over which end of a boiled egg should be broken in order to eat it, with Big Endians rebelling against a king who demanded his subjects break eggs at the little end.

The news today that Comcast is rolling out DOCSIS 4.0-based broadband to residential users in Colorado ahead of a wider rollout across its US markets serves as a reminder that there is a battle going on for broadband subscribers and that technology choices are still to be made. But how important are those technology choices, both for operators and for consumers? Are the choices between DOCSIS and fibre, and within DOCSIS between Remote PHY and Remote MACPHY or between Full Duplex and Extended Spectrum DOCSIS of vital importance – or are they analogous to Big Endians versus Little Endians.

For cable operators with legacy HFC networks, the main choice has been whether to continue upgrading those networks using advanced versions of the DOCSIS standard that has served them so well over two-plus decades or to go for broke by investing in full fibre networks to the home. (DOCSIS 4.0, as Comcast boasts, can deliver ultra-fast internet access, including symmetric bandwidth offerings, that are more than capable of holding their own with current patterns of use.)

The backdrop to this is that cable operator (and telecom operators with copper networks and DSL-based broadband footprints) are coming under increasing competitive pressure from fibre-to-the-home players. At the same time, all these ‘multi-play’ fixed-line service providers including cable have now for a long time looked on broadband as their primary offering (alongside fast-growing but more challenging mobile telephony and broadband). The other elements – pay TV in the age of streaming and fixed telephony in the age of mobiles – are seen as low margin, declining businesses.

The word ‘fibre’ has proved its marketing worth in recent years as a catch-all term for really fast broadband. Telesales reps routinely promise ‘fibre’ broadband because fibre is involved at some point in the infrastructure, even if not to the home. FTTH operators have meanwhile complained loudly about the use of ‘fibre’ as a word to market HFC broadband.

However, the fixed broadband technology choices facing historic cable operators are not straightforward. The optimal technology choice can depend on location, density of population, demand and the cost of deployment.

Fibre versus DOCSIS

In broad-brush terms, fibre is said to make sense in densely populated urban areas with a high concentration of MDUs (such is the case in much of Europe) while areas with populations thinly spread (in the kind of exurban sprawl characteristic of much of North America) are more suited to upgrading the existing HFC infrastructure.

In reality the calculation is more nuanced.

For a historic European cable operator such as Liberty Global (now a holding company with stakes in multiple operators in multiple countries), the broad rule of thumb is fibre-first.

Speaking on a Morgan Stanley CTO Symposium recently, Liberty CTO Enrique Rodriguez said that fibre was more energy-efficient than DOCSIS, and that in many cases the cost of upgrading HFC to fibre was much the same as upgrading to DOCSIS 4.0.

In the UK, he said, the cost was £600-650 per home for XGS PON fibre for a greenfield build.  However, looking at the upgrade cost per home across the existing cable network, the cost of upgrading to XGS PON was reduced to about £100, he said.

Liberty’s JV with mobile player Telefónica, Virgin Media O2, is therefore going for fibre. However, this isn’t seen as the optimal solution across Liberty’s entire European footprint. In the Netherlands, Liberty has not yet set a timeline for deployment of DOCSIS 4.0 for VodafoneZiggo, its JV with mobile player Vodafone, but it is moving in that direction, although DOCSIS 4.0 upgrades will not take place before 2025.

That is partly because Liberty can accommodate demand for higher speeds today with its existing technology, DOCSIS 3.1, in many cases.

In Switzerland, Liberty Global-backed Sunrise has previously said it will use wholesale fibre, but it will also launch 2.5Gbps on its existing DOCSIS 3.1 network. Rodriguez said that Liberty Global was able to leverage its DOCSIS 3.1 networks to deliver speeds as high as 2.5Gbps “even before we deploy DOCSIS 4.0 in the network”.

Upgrading to DOCSIS 4.0 requires operators also to implement a Distributed Access Architecture, which sees functions previously resident in a headend of hub distributed closer to the user to achieve efficiencies in hardware, speed, reliability, latency and security.

In the US, there has been a broad consensus about how to do this – the deployment of the technology known as Remote PHY (distributing the physical layer of the network), while in Europe the picture is much more fragmented, with very limited deployment of Distributed Access Architecture to date.

Europeans have however been ahead in the race to upgrade cable infrastructure to higher spectrum to deliver more capacity, with large-scale upgrades to 1.2GHz downstream.

Speaking at ANGA COM earlier this year, Hanno Narjus, SVP at Teleste Broadband Networks, predicted that some European operators will invest fully in DOCSIS 4.0 to give new life to their HFC plant over the next 10-15 years, while at the other extreme, operators want to move to fibre straightaway. In the middle there are operators who will extend the life of cable for the next five to 10 years while focusing on fibre in regions outside the existing coax network, he said.

The different choices to be made in Europe also reflect the fact that HFC cable has a much smaller footprint relative the overall broadband universe than in the US, where about 70% of homes are served by HFC cable (the figure in Europe is more like 30%). That distinction does however mask widespread differences within Europe between densely cable regions such as the Benelux and areas where cable is a minority challenger network such as the UK (or nonexistent, such as Italy).

Full Duplex versus Extended Spectrum

The picture is complicated further by the fact that there are multiple options available to upgrade HFC without going all out for fibre. Even if there is an emerging consensus about how to deploy Distributed Access Architecture (Remote PHY rather than Remote MACPHY), operators have a choice between Full Duplex DOCSIS (ideal for those looking to deploy symmetrical services) or Extended Spectrum DOCSIS (more appropriate for ultra-high speed downstream bandwidth). Full Duplex DOCSIS uses the same spectrum for downstream and upstream spectrum, while Extended Spectrum DOCSIS separates the two.

For operators the choice is in fact more meaningful than a Gulliver’s Travels dispute between Big and Little Endians. The advantages and disadvantages of each can depend on multiple factors including the topology of networks.

In Comcast’s case, the US cable giant has opted for Full Duplex DOCSIS, which is said to be more suitable for network topologies that require little maintenance. Comcast aims to market symmetric bandwidth services, perhaps indicating a concern about competition from FTTH players and greater demand for upstream capacity. While Full Duplex DOCSIS has until now required deep fibre and no amplifiers between the node and the home, Comcast is hopeful that Full Duplex DOCSIS amps from CommScope will be available soon giving it more flexibility in other regions.

Other big US cable operators like Charter and Cox have been leaning more towards Extended Spectrum DOCSIS, while Altice USA has been expensively deploying fibre.

The need to choose between the two could become a thing of the past thanks to ongoing technological developments. Liberty Global’s Rodriguez says that there are now software stacks available that can deal with both implementations at the same time, so the prospects to deliver a future-proof network using DOCSIS had improved markedly. Rodriguez argues that DOCSIS 4.0 can take cable to 10Gbps downstream with 4Gbps upstream, or perhaps symmetrical services with 8Gbps.

For the vast majority of consumers today, that is way more than enough. And while ‘fibre’ has been successfully used as a marketing tool as much as a technology choice, according to Rodriguez, there is little evidence of subscribers churning because their broadband supplier relies on DOCSIS rather than FTTH. (There are many other reasons why they do churn.)

For operators, there may be good reasons, for example, to choose between DOCSIS and fibre based on local circumstances and meaningful reasons to choose one flavour of DOCSIS over another.

For consumers, at least until applications catch up with the available bandwidth, the choice is more akin to deciding which end of your egg you prefer to crack.