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UPDATE Openreach Set UK G.fast Broadband ISP Fault Threshold at 100Mbps

Monday, March 20th, 2017 (12:54 pm) - Score 7,305

A few more details have leaked out today about Openreach’s (BT) new 330Mbps capable G.fast (ITU G.9700/9701) broadband technology, which among other things reveals that ISPs will be able to raise a fault if a customer’s line speed drops below a threshold of 100Mbps.

At present Openreach is currently expanding their G.fast pilot to cover 138,000 premises at up to 17 UK locations by the end of March 2017. You can find more details about this technology in our previous articles (examples here and here), although assuming all goes to plan then 10 million UK premises should be reached by 2020 and possibly many more by 2025, when the top speed might also be raised to 500Mbps.

However this pilot has also triggered the release of a lot more detail about the service and as a result it’s finally becoming easier to get answers to some of our longest held questions, not least of which is how Openreach plans to handle faults and at which point a line could be considered to be running too slowly (faulty).

gfast long openreach diagram

The key selling point of a product that is being promoted as “ultrafast” is obviously its high speed and so it makes sense for Openreach to confirm that they’ve set the threshold at 100Mbps, which is the point at which many people consider the “ultrafast” definition to start (admittedly Ofcom prefer 300Mbps).

So here are the thresholds on which ISPs will be able to raise a fault (note: the line itself may not necessarily have a fault at this level but providers can flag it for investigation).

G.fast Fault Thresholds

* If the speed falls below 100Mbps.

* If the speed falls below the Point of Sale forecast by Openreach’s eMLC [Enhanced Managed Line Characteristics] system.

* If the speed drops by more than 30% from the line rate they received when it was installed.

We should remind readers that G.fast will initially come in two main product flavours: Download speeds of up to 330Mbps (50Mbps upload) and Download speeds of up to 160Mbps (30Mbps upload). During BT’s early G.fast trials we also recall that only 3% of lines delivered speeds of less than 100Mbps and 75% got more than 300Mbps, although their approach has changed a bit since then (it’s now more cabinet focused instead of FTTdp).

The latest engineering documentation from Openreach also says that G.fast, like similar DSL technologies, is generally being targeted at copper local loops of shorter than 500 metres, which makes sense because past this point the performance is much more akin to existing services (e.g. FTTC/VDSL2) and drops off much more quickly over distance. See our hybrid fibre technology page for a chart.

The update then notes that they have “performance targets” of 150Mbps for local loops shorter than 500 metres and it confirms how they’ve designated 350 metres or less for their highest G.fast speeds, which is something that has been known for awhile (here); even if they can’t quite yet deliver 300Mbps over 350 metres of copper (here).

Elsewhere Openreach confirms that the hybrid cable (fibre optic and power supply), which links their new 48 port G.fast pods (situated on the side of existing PCP street cabinets) to the nearby FTTC / DSLAM street cabinet, will have a reach of up to 100 metres. The cable itself contains 3 x 10mm2 conductors and a 12 fibre unit.

Speaking of pods, we’ve previously reported that Nokia / Huawei should eventually allow them to handle 96 ports and the latest update says to expect this “in future months“. Vectoring 96 ports is a huge challenge and it’s not yet ready for prime time, although initial G.fast uptake probably won’t be as high as it was for VDSL2 and that should offer some breathing room.

UPDATE 24th March 2017

Openreach informs that they hope to have 96 port capable hardware in their hands during this summer.

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By Mark Jackson
Mark is a professional technology writer, IT consultant and computer engineer from Dorset (England), he also founded ISPreview in 1999 and enjoys analysing the latest telecoms and broadband developments. Find me on Twitter, , Facebook and Linkedin.
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13 Responses
  1. Frank Butcher says:

    10mm2 conductors seems quite chunky if correct, I wonder what sort of power draw they are expecting from the G.Fast unit?

    1. Mark Jackson says:

      Only bit of info. I could find suggests that the electrical supply is “(-48 volt DC)”.

    2. Frank Butcher says:

      Interesting, if it’s 48v DC then that explains the increased conductor size.

      I initially thought it would be 230v straight from the FTTC cab supply, but I guess they will be using the existing FTTC cab PSU and battery back up to supply the G.Fast node to reduce the space & weight requirements of the side pod.

    3. Steve Jones says:

      @Frank Butcher

      They will not doubt be running power down the same ducting that carries the tie cables as digging new ducting for power would add considerably to the costs, especially as the local supply company will charge a not inconsiderably amount of money to connect it.

      One thing that Openreach will not allow (indeed no telco will) is to run mains cables in the same ducting as telephone cables. Not only is it potentially highly dangerous (imagine if it filled with water – not unusual in ducting), but it could add to electrical noise.

      If these pods are to support up to 96 cables, and we allow 5W each, then that’s about 500W or around 10 amps. Way, way below the capacity of a 10mm^2 cable, but voltage drop is always the enemy of LV systems. Even so, it sounds rather bigger than I’d expect and there’s three of them. However, it’s only the thickness used on some electric showers and cookers (which has three cores).

    4. Peter Taylor says:

      The cables sharing the same duct will be power and fibre only. No copper comms cables will be sharing ducts with power cables.

    5. MikeW says:

      Except those copper comms cables are all power supplies too. -48V on every single pair.
      Not a lot of current though.

    6. MikeW says:

      There’s a good picture of the ducting used in the based of a Huawei 288 here:

      It isn’t obvious which duct the existing fibre comes in on. There is one “unexplainable” duct on the DSLAM side which could be used. However, other pictures suggest the fibre termination trays are actually in the copper/IDC compartment, suggesting the fibre comes in alongside the copper tie pairs.

      The pictures in the link showing the duct runs from the chamber also only show the two large ducts, which back up the idea the fibre runs alongside the tie pairs.

      It does make me wonder where the new combined-fibre-power cable will go from DSLAM to chamber if it doesn’t reuse one of those 2 tie-pair ducts. Would they really dig in new ducts from DSLAM to chamber, and from chamber to PCP?

  2. Robert Scriven says:

    So much for pods on poles, i shall just stick to my 15mb shall i? FAST GET FASTER!!!!

    1. CarlT says:

      For right now yes indeed Robert.

  3. Rich G says:

    330mb? I’m on a fibre enabled cabinet, but due to distance I’m not allowed FTTC service. As a result, i rarely achieve a full 1Mbps download, and reliability is non existent.

    This service costs the same as a neighbour who will comfortably get Infinity. FmL.

  4. Sarah Ellis says:

    Don’t make me laugh! 100mbps! Our speed is 1.5mbps as we are too far from our already enabled for fibre cabinet to get anthing faster. You think they should be putting in more cabinets to deal with this issue first.

  5. Cecil Ward says:

    Tell you what, you can have 300Mbps when I get 3Mbps, is that fair enough? But not before. The authorities seem to have lost their minds. Sort out the worst, first.

    1. Lee says:

      Openreach’s commercial deployments cannot be controlled by “the authorities”

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