Openreach shaves £10m off FTTP rollout cost with a 'subtended headend'

BT’s networks arm Openreach is making progress with its new-ish approach to getting fibre into hard-to-reach areas.

The Openreach press release calls the tech it’s using a ‘subtended headend’, but beyond saying that they are installed in street cabinets, pretty much leaves it at that when it comes to explaining what they actually are.

However, the name also crops up in an ISPreview article from 2019, which explains that it’s another name for a shrunken optical line terminal (OLT) – the box that connects the fibre coming from the modems installed in the user’s premises (also known as the optical network terminal (ONT)) to the backbone network.

Due to their size, a typical OLT tends to be deployed in a local exchange. This is fine under most circumstances because the premises they serve are close enough to not cause any issues. But their performance is limited once you get beyond a certain distance, and that can become a problem in sparsely-populated areas where multiple rural communities are served by a single exchange.

Enter the subtended headend (SHE). It is small enough to fit into a street cabinet – which is deployed much closer to the customer and being part of the fibre-to-the-cabinet (FTTC) network is already connected by fibre to the local exchange. Using a SHE therefore doesn’t require Openreach to extend its backbone network or build new exchanges.

Their value then is plain to see.

Openreach said last Thursday that it has deployed around 100 SHEs across the UK, connecting 160,000 premises that would otherwise be too costly to serve with FTTP.

Indeed, cost per premises is arguably the biggest single barrier to rural fibre deployment. Getting the figure low enough can mean the difference between closing the digital divide and leaving it open, at least when it comes to fixed-line services, that is.

In 2019, Ofcom estimated (PDF) that the capex per premises passed by FTTP would weigh in at around £500 for the first 21 million or so, but then rise rapidly to almost £2,500 for the final 2-3 million.

Given what inflation is doing to the cost of materials and capital, that estimate is probably looking a little optimistic today.

Openreach said that a single SHE location has the capacity to connect up to 1,000 additional homes and businesses. Their use has reduced build time by up to six months, and it removes the cost of those aforementioned new exchanges and backbone infrastructure.

Openreach says that by using SHEs it has avoided having to build 1,262 km of backbone network and in the process saved it £10 million in the last financial year alone.

“We’re rolling out full fibre to reach 25m homes and businesses and a quarter of that – around 6m premises – will be in the hardest to reach third of the country,” said Openreach’s chief engineer Andy Whale, in a statement. “We’ve already built full fibre to around half of those harder to reach homes and businesses and this innovation is helping us to build faster and further into these more remote parts the country – especially in more rural areas, on a very large scale but more efficiently and at a much lower cost.”

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