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Photos: How BT's FTTH fibre broadband gets inside your home

Fibre to the home broadband - from the exchange to a box on your wall...
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By Natasha Lomas on
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1 of 15 Natasha Lomas/silicon.com

Fibre to the home broadband - from the exchange to a box on your wall...

Very high speed broadband technology has been common in Far East nations such as Hong Kong and South Korea for years, but UK telco BT is only now taking the first steps to roll out commercial fibre to the home (FTTH) broadband services.

After installing full fibre in a new housing development in Ebbsfleet, Kent, a few years ago, BT has not rushed into a mass rollout of FTTH. Instead it has focused on limited trials - kicking the tyres of the tech in Milton Keynes and London this year.

Even though FTTH is the fastest of BT's upcoming superfast broadband offerings - it supports up to 100Mbps - FTTH will also be the minority technology in its rollout. A quarter of BT's planned fibre rollout will be FTTH versus three-quarters fibre to the cabinet (FTTC), which supports a 40Mbps service.

The issue is cost: FTTH is much more expensive to install than FTTC as the fibre has to be laid much further and all installed by hand. While FTTC terminates in BT's street cabinets, FTTH requires the line to run right up to people's doorsteps and on inside individual premises - requiring Openreach engineers to get on their knees and rod and rope cable through street sub-ducts - or hang it overhead from telegraph poles.

The telecoms provider says it is aiming for a mixed economy approach to fibre deployments - installing a mix of both FTTH and FTTC depending on what the local conditions at each cabinet are conducive to.

At its Bradwell Abbey exchange in Milton Keynes, BT showed off some of the extra kit and processes involved in FTTH network deployments.

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The kit that will get superfast FTTH broadband into people's homes will mostly be hidden underground - in BT duct boxes such as the one pictured above. Overhead telegraph poles could also be used to deliver fibre in some areas where ducts do not exist or are blocked or too congested to stuff with more kit.

Telecoms regulator Ofcom has stipulated BT must open up access to its ducts and poles to rival ISPs - so in future other comms providers might be squeezing their own kit into BT's boxes.

But the duct box above is only one element of the broadband network. From the exchange the next step is the aggregation node, then the splitter node, distribution nodes and manifolds, and eventually - when an individual customer signs up for the FTTH service - ending up via a customer splice point at an optical network termination point inside their home.

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Here a BT engineer shows a map of one of the FTTH trial areas in Milton Keynes, with the map showing BT's sub-ducts and joint boxes marked in black, top. These boxes and sub-ducts are used for the BT's existing copper-based broadband network - and are now being reused for superfast broadband.

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In the fibre's journey from the exchange towards your home, the first stop is a node in BT's exchanges, which aggregates the fibre - known as an aggregation node. After that comes the splitter node, above, where individual fibre elements - each containing 12 separate fibres - are split out into multiple outputs.

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Here are the fibre elements loosely coiled between the trays on the splitter where the engineer can remove them for splicing.

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The individual fibres have colour-coded resin sheaths that have to be stripped away when splicing the fibres together. The actual fibre is a little smaller than a human hair and about half the size of the sheathed line, notes the engineer.

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Individual fibres are fed into trays on the splitter and spliced onto a silver filter using a technique called fusion splicing.

"You have one fibre going in and then, through a miracle of modern science, that is split 32 ways so you've got 32 output legs coming out from there," said a BT engineer.

Each of the fibres is capable of feeding 32 customers but BT only uses 30 of the outputs, leaving two spare for "maintenance purposes", he adds.

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From the splitter the fibres are connected to the sub-duct cabling that goes towards individual residences and to the next stage in the FTTH network: the distribution point - pictured above on the right. Distribution points are typically sited within 60 metres of the individual premises covered by the FTTH network, according to BT.

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Here's a close-up of the inside of one of the trays on the distribution point. The fibres are not spliced onto the trays until a customer has signed up to get the superfast FTTH service.

"The splicing is relatively simple - the difficult bit is managing the fibres in these trays and making sure you don't break it," noted the engineer. "Making sure you get exactly the right length so that when you take the fibres out and you have to coil it all back you get it so that the actual joint protection for that splice is accurately positioned in the centre of the tray. That's where the skill lies. Not pressing a button on the fusion splicer, it's fitting it in all these trays."

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Here's the distribution node in its normal habit: underground in a BT duct box.

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And here the distribution point has been lifted clear of the duct box and had its black casing removed to reveal the familiar trays. The coloured tubes indicated by the engineer are awaiting blown fibre and have been capped off with seals to prevent water getting inside.

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12 of 15 Natasha Lomas/silicon.com

To carry the fibre between duct boxes, BT is using a new type of mini-duct cable with a smaller diameter - the black and yellow tube pictured above - than it has traditionally used elsewhere in its network. The mini-duct cable is 6.4mm compared with the usual 15-16mm grade pipes to save on space in congested ducts. The cable contains 12 smaller tubes into which the fibre bundles are installed by blowing with compressed air.

One end of the sub-duct is connected to a manifold - the black plastic flute being pointed out above and also in the engineer's hand. Manifolds can be fitted above ground on the side of telegraph poles for overhead fibre installations or underground in ducts.

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Here's a manifold in its natural habitat - with sub-duct coming in to one half and 3mm-wide drop tube coming out the other end. Like all the FTTH cabling, the drop tube has to be pulled by hand by the engineers to get the fibre to the customer's home.

BT installs a manifold for every duct box in the Milton Keynes FTTH area, which feeds up to 12 properties. "So we've had to put a significant amount of manifolds into the ground," the engineer adds.

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Once a customer signs up to get FTTH, BT Openreach returns to the area to complete the installation. An engineer installs a customer splice point, shown above, outside the premises, close to where the drop tube emerges.

"This will have a splice in it and this is where we marry up with the external network," notes the engineer.

The Openreach engineer will have to locate the correct manifold for the individual residence, along with its local distribution point, which can be up to 400 metres away. Then the engineer will start fibre blowing, splicing and rodding and roping the fibre to get it to the doorstep and into the splice point.

Next BT runs up to 30 metres of rubberised cable on into and around the customer's property to connect the network into the final bit of Openreach kit: an optical network termination point (ONT).

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Here's the optical network termination point - the end of the line for Openreach's fibre and the box where customers plug in their own router. In addition to installing the box, Openreach connects a red light source to the fibre so the individual customer's live line gives a visible output on the ONT.

The final few metres of the FTTH installation process - taking the fibre from the distribution point and manifold into the customer's house to terminate at a box on their wall - takes an average of seven and a half hours, according to the engineer.

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