How do you fix a fixed line break? Here's how our engineers find one snapped cable among hundreds of miles of fibre.

Earlier this month we shone a light on some of the surprising and unpredictable things that can cause fixed line networks – one of which keeps Vodafone Broadband ticking – to break. But if we spot a break on our network, how do we find it among underground cables covering thousands of miles?

To find out, we’ve been speaking to Bill Robertson, one of our more than 300 field engineers, who has over 15 years’ experience ‘walking the line’.

Part one: Narrowing things down

Bill fibre engineer“In the first case, our Network Operations Team (NOC) team will spot the fault and try to get things resolved remotely,” Bill says. “But if they can’t do that, they’ll send an engineer out.” And in many cases, that’s Bill. But what’s step one when you have so much cable to sift through? “By the time the engineer arrives, the NOC will already have a good idea whether it’s a power failure, a technical fault or a fibre break, but you can’t tell for sure until you get on site.”

If it is a fibre break, that’s when the fun begins. Thankfully, though, our engineers aren’t flying blind; they’ve got some sophisticated tech up their sleeves which helps pinpoint where the break might be…

“We use an Optical Time Domain Reflectometer (OTDR),” Bill explains, “which is a bit of kit that sends light down the length of the fibre cable in a loop. When the light comes back, it’ll calculate how long the working cable is, and with that information we can see how far away the line break is from our location.

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“The older OTDRs, which we’ve used for 15 years, get you within half a kilometre of the break, but the newer ones are as accurate as 10 metres – so they’re really useful in helping us find the break quickly, which means we can get everything back up and running as soon as possible.”

The trick is to use more than one of these OTDRs at the same time, coming at the problem from different ends to get a much clearer idea of where along our vast stretches of cable the fault might be. And when we say vast, we mean it:

“Recently I was at Salisbury, another engineer was at Southampton, and there was a fault near Reading. The OTDR in Southampton saw the break as being 40km away, and I saw it as being 13.5km away. Once you’ve got that information, you can work out whereabouts the break is.”

Part two: I walk the line

With us so far? We’ve now found the rough area in which we’ve had a fibre break. The next step is to figure out exactly where it is, and to assess the damage. And that’s where access pits come in.

“These pits can be anything from 1km to 10-20km apart,” he says. “They’re about two yards long and a yard deep, and the plastic tunnelling that carries all the fibre runs through the middle.

“Once we know, with the help of the OTDRs, where the pits before and after the line break are, we then have to walk from one to the other to find out what’s caused the break, and how bad it is. If the cable’s been sliced all the way through by a falling beam, for instance, you’ll have to lay a huge amount of new cable – which will take more time than fixing a smaller issue, such as a rat chewing through part of the cable.”

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But it’s not easy going. Because our cables run the length and breadth of the country, which means we can bring our broadband service to 80% of the UK population, the ease of getting to each pit varies wildly – sometimes it’s a walk in the park, and sometimes it’s a midnight hike through the back o’ beyond:

“In our last break, eight fibres out of 92 fibres were broken,” Bill explains. “The first pit was ok because it was on the pavement to the side of a road. But the second pit was in the middle of a country road. And in those instances we needed to contact the council and get permission to put up temporary traffic lights. If it’s a dual carriageway, you’re going to need permission from the police or the Highways Agency as well, all of which delays us from getting that particular fibre cable back up and running.

“The other problems with pits are that they’re below street level, which means there tends to be a good couple of feet of water in each one. So they’re not the most pleasant places to jump in to!”

Part three: Calling in reinforcements

Bearing in mind that most of these cables run underground, it’s normally something obvious – like building work – that’s caused the break. But there’s a big difference between all the cables in a particular tunnel having been severed, and only a few. And how Bill and our engineers deal with them differs depending on the problem:

“Pits tend to have spare coils of fibre lying in the bottom of them,” Bill says, “so that if there’s a break in the middle you can pull them out and join the fibre together from inside the pit. That will only take about 20 minutes. But if the fibre is broken completely and you didn’t have that extra cabling, we won’t be able to join it on the spot.”

And if that’s the case, it’s time to call in reinforcements.

“We walk from one pit to the other to find out what’s caused the break…

“Fixing fibre is a very specific role, so when we need to splice and fix it we’ll phone up the NOC, and they’ll deploy a specialist fibre team. If we’ve been able to determine the distance of the break from where we are, and the ID number of the cable trunk, then they’ll be able to get things sorted.

“If we have to lay a whole new cable, they have to pull it all through the tunnel using a process called ‘jetting’, which pushes the cable through the pipe using air. And that can take a whole day. But the main problem – the bit which takes the most time – is finding the break, and deciding whether we need new fibres or if we can fix the existing ones.”

Fortunately, fibre breaks are rare. And what’s more, we’re doing what we can to speed up every step of the fixing process for when a cable get damaged, including issuing our engineers with hundreds of the new OTDRs.

“There will always be a delay between the NOC getting a signal to say that the line has broken, the engineer getting to the relevant pits and figuring out where the break is, and then getting things fixed,” says Bill in closing. “There’ll always be that, but we’re working hard to speed up every one of those steps.”

What causes a break? Discover some of the surprising things that can affect our fixed line network here.