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BT Reveal Tech Details for Expanded Long Reach VDSL Broadband Trial

Tuesday, August 9th, 2016 (12:33 pm) - Score 9,866

Openreach (BT) has today published new technical details for their on-going trials of fixed line “Long Reach VDSL” (FTTC) broadband technology, which could be used to deliver the future 10Mbps Universal Service Obligation and possibly even to expand the availability of “superfast” (24Mbps+) speeds.

We’ll begin with a quick recap. The existing ‘up to’ 40-80Mbps capable Fibre-to-the-Cabinet (FTTC) service works by running a fibre optic cable from the telephone exchange to your local street cabinet. After that Openreach uses VDSL2 over the remaining copper wire, which runs from the cabinet and into your home.

Ideally you need to live less than 300-400 metres (copper line length) from your street cabinet to get the best VDSL2 speeds, with performance falling away to around just 10-15Mbps at the extremes of 2000 metres (2km). But many premises can exist a lot further away than this and so LR-VDSL was proposed as one possible way of meeting the Government’s 10Mbps USO pledge.

The new approach is said to work in a narrower frequency band and at a higher power than existing VDSL2 connections, with lab tests showing that a 2km long copper line delivering 9Mbps via normal VDSL2 could be pushed to 24Mbps+ with LR-VDSL (here). A technical Proof of Concept Trial with up to 200 lines has already taken place in the rural village of Isfield (East Sussex).

long reach vdsl2 fttc performance prediction

By comparison the new SIN522 (PDF) document gives us our first real look at how the technology is setup and also confirms that Openreach will this month launch an expanded trial “across a number of exchange areas” (we’ve asked for a list of the locations and have sadly been refused by BT).

At this point it’s worth noting that the first concept trial in Isfield needed to ensure that no exchange based ADSL existed in order to prevent crossover network interference. The new trials also warn about the “potential degradation to ADSL services from application of LR-VDSL” and have recommended that ISPs cancel any SMPF (Shared LLU Line) based services in order to take advantage of the trial (there aren’t many of these left in the UK, so it’s not likely to be a big issue).

CPs will not be able order SMPF on any of the Trial Cabinets but may order MPF subject to an acknowledgement that any ADSL service they want to offer will be impacted by LR-VDSL and that, in the circumstances, we strongly recommend they use GEA FTTC for broadband services,” said BT’s document.

We also note some other requirements, such as the need to enable G.INP and also Vectoring to help cancel out cross-talk interference (so far Openreach has only made minimal use of this on VDSL, partly because future G.fast upgrades are regarded as a better investment). On top of that G.INP has had somewhat of a rocky roll-out due to conflicts with ECI kit (here).

LR-VDSL is also being aimed at lines with a D-side length in excess of 1.25km (0.5mm diameter copper) and Seamless Rate Adaptation (SRA) may even be applied to some of the LR-VDSL lines as part of Openreach’s trial activity.

2.2 LR-VDSL Line Selection

In order for a line to be selected for uplifting to LR-VDSL, the following criteria must be met:

1) The D-side insertion loss (measured at 300kHz) of the line shall be greater than 12.5dB and less than 40 dB (both measured at 300kHz). Lines with a loss lower than this will not benefit from LR-VDSL and will remain as a 17MHz vectored VDSL2 line.

2) The CP shall have confirmed to Openreach Product Line that they are prepared to participate in the trial activity.

3) The CP provided CPE shall support Profile 8b operation and vectoring as defined in G.993.2 and G.993.5.

The LR-VDSL trial will only use a single profile and related lines will be configured for a default downstream target margin of 6dB, although some lines may be migrated to operate with lower target margins to “determine what impact this has on [broadband] speed and stability“. Interestingly LR-VDSL will use the VDSL2 band plan 998 (B8-4), which defines a maximum frequency of 12MHz (i.e. less than the 17.664MHz used by normal VDSL2 / FTTC lines).

The current VDSL2 system also has a maximum aggregate transmit power of 14.5dBm in both the upstream and downstream directions, while LR-VDSL will need to push this higher and aims to use 20.5dBm in the downstream direction and 14.5dBm in the upstream direction (i.e. the main focus here is on boosting download speeds by using less frequency and more power).

Apparently it’s expected that customers uplifted to LR-VDSL shall receive a maximum service rate of 40Mbps downstream and 10Mbps upstream, although many will obviously receive less than this.

All in all there’s plenty of useful information to chew on and we’ll finish by posting the full channel, line and spectrum configuration profiles for LR-VDSL. Anybody not familiar with this bit can switch away to read something else, but it’s useful to have confirmation of how the technology will actually work.


Leave a Comment
31 Responses
  1. Phil Coates says:

    Yep, still 0 Mbps at my exchange distance.

    I am sure its very clever but isn’t this an example of the much criticized ‘sweating the copper assets’?

    1. Gadget says:

      one person’s “sweating the assets” is another’s “providing a commercial viable solution where none currently exists”

    2. Steve Jones says:

      There is nothing wrong in principle with “sweating the assets”…

  2. Phil Coates says:

    True, but the new tech extends 10Mbps by 1km v’s Extended VDSL 1 which extends VDSL2 by 500m at that speed. At 7km from my exchange its all irrelevant anyway. What is particularly irksome is that our village has a Fibre Cab 1500m away but its fed from an exchange in the opposite direction to which I am actually geographically nearer.

    Network design eh!!

    1. dragoneast says:

      Yep, good ole UK. Like the road network it wasn’t so much “designed” (well in the case of the the roads, after the Romans), it just grew, with bits tagged on whatever seemed most convenient, or possible, at the time. It’s the way we do things. It’s cheaper at the time, and less useful too. And just try changing anything. We don’t, unless we can be persuaded that nothing is changing at all. (The lesson some people forgot). Make do and mend is hardwired in the national psyche. It’s parsimony, which we mistake for efficiency.

      I don’t think there’s anything (at least in the UK) that can’t be explained by history (“that’s just how we do it”). Stick-in-the-muds.

    2. fasman says:

      phil coates the distance to your exchange is almost an irrelevance its the distance you are to your cab (assuming your cab is enabled)

  3. craski says:

    Sounds like it could benefit plenty people.
    When referring to LR VDSL within the article does that mean VDSL2 Long Reach 1 and VDSL2 Long Reach 2?

    1. craski says:

      *or* not *and*

  4. Phil Spencer says:

    “recommended that ISPs cancel any SMPF (Shared LLU Line) based services in order to take advantage of the trial (there aren’t many of these left in the UK, so it’s not likely to be a big issue)” – Any ISP that uses BTWholesale will be on SMPF so probably a fair few million lines altogether especially as every BT line will be SMPF plus Plusnet and probably Zen and EE. Wouldn’t surprise me if TalkTalk and Sky had some too.

    1. MikeW says:

      Doesn’t SMPF imply two CPs: one voice, one broadband, sharing the metallic path, both attaching equipment at the exchange?

      So SMPF happens when BTW supply voice, and an LLU ISP supplies broadband.

      It isn’t considered SMPF if BTW supply both voice and exchange-based ADSL broadband, nor when a GEA service is used to provide broadband.

  5. Walter G M Willcox says:

    Noting that ADSL services must be removed, what will be provided for those consumers at distances way beyond those discussed here ?

    The real solutions being provided by others deliver 1,000 Mbps both upstream and downstream at ALL line lengths via true point-to-point Fibre to the Home.

    This appears to be yet more “jam tomorrow” to distract from the current rural mayhem.

    1. Richard says:

      We’d all love proper fibre, but it’s just not practical at a vaguely attainable price.

      I’m stuck on sub 5Mbit/s broadband (cabinet is scheduled for upgrade within 12 months under Superfast Essex BDUK scheme) so know your pain.

    2. fasman says:


      no ADSL services will be removed as you cannot force a subscriber to VDSL by worsening ADSL or removing ADSL– don’t forget there are in excess of 400 service provider who consume copper only from openreach and not Ethernet GEA products this will enable chose connected to an enabled ab and want fibre to gain a fibre product at a greater distance

    3. FibreFred says:

      Get the others to deliver then Walter?

      Meanwhile this is a possible solution within an acceptable budget to deliver the USO

  6. Phil Coates says:

    @Fasman. My cabinet is about 100m from the Exchange so 6.9km is the distance to my house.

  7. Balb0wa says:

    I think it looks good as well to people on low speeds on fttc, me @ 13mb and 760k up!! id love to trial it.

    Im on a 40/2 profile , i suppose they will do away with this profile eventually then.

  8. captain.cretin says:

    I have friends who get 200Kb on a good day, they would be thrilled to get 5Mb, let alone 10.

  9. Cooper says:

    Seems mad to introduce more complexity just to meet a non-ambitious 10Mbps USO. Where is the upgrade path for the future for those stuck with technology based on cooper that only just meets the USO?

    1. captain.cretin says:

      I agree, BT are being very short sighted.

      With the increasing number of copper thefts, the rising price of copper, and its last century limitations, BT should have started planning a decade ago, and started to roll out PURE fibre connections to every property by now.

      They SHOULD NOT be installing copper on new exchanges, new connections to houses or exchange upgrades; they should be replacing the copper in each cab with FTTP; yet they still dont have the equipment in the cab/exchange to do this.

      Someone will pop up (probably paid by BT), and mention the cost; yes it will cost, but none of the figures BT put out allow for the scrap price of the copper; I read somewhere a few years back that BT is actually VALUED at less than the value of the copper in its phone lines.

    2. TheManStan says:

      Um…. a decade ago BT were not allowed to have fibre to home products…

    3. REGIS says:

      check your history capt. BT where forbidden to roll out ftth because of the “cable” companies saying they couldn’t compete…… you want to have a go at someone then start with the government and ofcom then ask yourself why is none of the big names (sky for example) doing there own fibre even tho they have been able to for years thanks to ofcom……… HINT: they don’t want to shoulder the cost of something they know is in very limited demand outside of the business sector but can whine for someone else to do all the work and then piggy back onto it for as little as possible while charging their customers as much as they think they can get away with.

      While i would never wish openreach and there teams of hard working employees any bad fortune part of me want to see them split up as everyone else wants and for it to totally fail and collapse….. lets see how many of the whiners then step up and say “we will take over” or “here let us help”….. nope every one of them will just whine even more.

      PS yes i know sky and talk talk are doing their own “trial FTTH” but sky have already said they are not going further with it and lets be honest its soooooooo far behind now it may as well be classed as “failed”.

  10. captain.cretin says:

    I said “started planning” a decade ago; and I didnt mean specifically for BB, but for everything, with the right equipment, voice is no more a problem than data down a fibre line, as that’s all it is – data.

    RIGHT NOW, BTOR should be supplying new cabs with fibre only, and the lines to customers houses should be fibre, with whatever equipment needed at the customer end to make voice calls (ie a VOIP interface), even if the customer hasnt ordered Fibre broadband.
    There should also be a planed roll-out to replace all the older cabs and lines with pure fibre; its not as if they dont charge us enough that they cant afford it (yes they can, they hide the profits by shuffling them around all their subsidiaries, like all evil multinationals do.

    1. TheManStan says:

      So national infrastructure plans like that take money…
      BT have a duty to theirr shareholder to publicise expenditures of this nature…
      OFCOM in turn would say you are not allowed to do this, it against the law (Enterprise Act 2002) and you have to stop…
      Oh and here we’ve arranged for the courts for you to have this fine!

    2. Chris P says:

      its called 21CN and BT started rolling this out some time ago. All calls over 21cn are effectively voip. Its what enables A/VDSL now


    3. MikeW says:

      Are you sure all calls are VoIP?

      21CN was indeed designed to carry voice in the way described in that article, but this approach was largely abandoned in 2009, and the only voice calls carried by 21CN are ones from the original “pathfinder” trials in South Wales.

      This 2015 report has a few things to say:

      eg “Cartesian understands that the amount of voice traffic delivered using the 21CN network is non-material.”

      In this 2011 report from BT, they say similar stuff:

      eg, in a section titled “NGN takes a backseat”, they say “The scaling back of BT’s 21CN plans followed announcements in previous years that BT would no longer develop a voice solution or a converged voice and broadband solution over the platform.”

      21CN certainly underpins BT’s ADSL2+, FTTC and FTTP services. But does not yet carry a significant volume of voice traffic as a PSTN replacement.

  11. fasman says:

    captain you clearly have no understanding no how the market operates and what Openreach is allowed to do as part of its condition of licence —

    so you like to put out of business/ or significantly disadvantage the significant number of communication providers that only consume copper from Openreach and do not consume Ethernet GEA

    the last secntence is untrue, incorrect and frankly ridiculous

  12. Stuart Fawcett says:

    At what point will BT drop the PSTN network altogether and let VOIP take over – at that point those with very slow ADSL speeds might no longer be able to get phone services! Well not unless mobile operators are offering alternate coverage.

    Then local power cuts will mean end users can’t make calls.
    Thousands of legacy users will be forced to use new voip phones.

    With power and water companies also delivering ‘piped’ services why can’t some aggregation occur?

    1. Chris P says:


      Voice calls already are VOIP, just not from the consumers handset.

    2. MikeW says:

      As mentioned in a reply above, 21CN didn’t turn out to be a PSTN replacement, and voice isn’t yet transferred behind the scenes as VoIP.

      However, BT have been talking about the prospect of turning off the PSTN by 2025 – though this will need agreement with Ofcom, as the UK needs to remove the USO on BT to supply a copper line voice service for this to happen.

      As it turns out, Ofcom are in discussions over a broadband USO (10Mbps), with the government having an intention of this being in place by 2020. It wouldn’t surprise me for BT and Ofcom to use this as an opportunity for the old voice USO to be replaced by the broadband USO, and for voice to be incorporated merely as “a service” (ie as VoIP).

      Right now, BT are gradually introducing a new product into their back-end systems known as SOGEA. This product is one that allows GEA-based broadband products to be ordered as the only product on a line (unlike today, where BT’s backend systems require you have a voice product on a line, and a broadband product added to it as a secondary product).

      Those changes will allow broadband to become the primary product on the line … to which VoIP voice service could be added as something separate – and perhaps not even known to Openreach.

      I’d expect BT to attempt to migrate people to SOGEA+VoIP service from 2018/19, giving them 6 years to ramp up the migration, allowing a switch-off of the PSTN to be considered.

  13. Cooper says:

    Where is the upgrade path?

    1. FibreFred says:

      Unknown at present maybe future advances in dsl tech or someone will have to stump up for the cost of fttp.

      It’s an endless argument I’m afraid, rolling out fttp to remote locations costs a lot of money. You either pay for most of that yourself upfront or the provider gets it back slowly over time. If bt were not hamstrung by ofcom and they didn’t have to wholesale I reckon we would see more fttp as they are guaranteed to get their money back over a certain period of time. However as it is now nothing is certain I can’t see them taking a risk investing in lots of rural fttp as they would have no idea when they would get there return.

      I’ve said it before and I will say it again, there are other providers why aren’t they serving you?

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