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UPDATE BT Enable Physical Retransmission G.INP on FTTC Broadband Lines

Tuesday, January 20th, 2015 (10:12 am) - Score 8,795

A new report appears to suggest that BTOpenreach has deployed or started to deploy Physical Retransmission (G.INP / ITU G.998.4) technology to improve the performance of their superfast ‘up to’ 40-80Mbps capable Fibre-to-the-Cabinet (FTTC / VDSL) broadband lines. Previously G.INP has only formed part of a trial on Openreach’s platform.

Openreach has already conducted a “limited trial” of G.INP with a small number of FTTC/VDSL lines during 2013 (here) and they expanded this last year as part of their Phase 2 FTTC Vectoring trials (here). The error correction technology is designed to tackle spikes / burst of electromagnetic interference (impulse noise) and can thus make some problematic lines more stable and less prone to errors (Sky Broadband already uses G.INP on their LLU network), which may also return a small performance benefit.

According to Thinkbroadband, a number of people have now reported that G.INP is suddenly showing up as being enabled on their FTTC broadband lines and this appears to be happening outside of the known trial locations for the Vectoring and G.INP technologies. We have recently been requesting more information on this and other matters from Openreach, although they have yet to clarify whether the change is part of an expanded trial or full deployment.

Last week Alcatel-Lucent described G.INP, especially when combined with Vectoring technology to iron out crosstalk interference, as “the secret to stable 100Mbps over copper“.

Alcatel-Lucent’s Jan Verlinden said:

Any appliance with an electric motor, power switch or power adapter is capable of generating impulse noise. Telephone wiring in subscribers’ homes picks up the noise from such appliances which, in turn, impairs DSL transmission. The severity depends on how close the source of the impairment is to the telephone wiring and the quality of the wiring itself. Service providers tell us, however, that many of their subscribers’ homes have lower quality wiring, so are susceptible to impairment.

Impulse noise comes in two main flavors – intermittent and repetitive. Noise that occurs as sporadic, unpredictable events is called SHINE (single high impulse noise event). SHINE often originates from turning an appliance on or off. Impulse noise that is consistent is known as REIN (repetitive electrical impulse noise). Household dimmers and faulty power adaptors are a common source of REIN.

The G.inp standard specifies the use of physical layer retransmission to enhance INP. The approach is similar to the retransmission method used in TCP/IP. Instead of IP packets, however, data transfer units (DTU) are sent between transmitter and receiver. When packets get corrupted during transmission, the transmitting peer is informed and the DTU is resent.

There are several benefits to the G.inp approach. Compared to I-FEC, the method only consumes transmission capacity when retransmission is required, traditionally consuming less than 1% (more on that later). And unlike TCP/IP, all the traffic is protected, including TCP, IP, UDP, SMTP, HTTP and more.

In addition, the round-trip time — i.e., the (minimum) time required for retransmission — is very short in case of G.inp because the DTU error detection and retransmission occurs at the physical layer.. TCP/IP retransmission often takes up to 50 milliseconds, while G.inp only takes a couple of milliseconds (4 milliseconds is typical). The result is also that G.inp achieves enhanced INP with good efficiency at shorter delays compared to I-FEC.”

We hope to have an update soon.

UPDATE 6:08pm

A spokesperson for Openreach has confirmed that G.INP is indeed being deployed and the roll-out should take several months. A commercial deployment of Vectoring technology now seems likely to follow.

An Openreach Spokeswoman told ISPreview.co.uk:

Openreach is in the early stages of introducing G.INP correction, also known as Retransmission, for FTTC lines that we think can benefit from it. Retransmission supports our Dynamic Line Management process and will benefit customers by providing a slight improvement in speed on FTTC lines where it has been used. It will also improve the volume of FTTC lines running error free.

FTTC lines will automatically accept Retransmission policies. Those currently with non-Retransmission compliant modem firmware will be identified by management systems and updated, after which Retransmission will become available.

An upgrade process has started which is expected to take several months to complete.”

Leave a Comment
25 Responses
  1. HmmmUK says:

    I replied via Twitter – but there’s more room here! 🙂

    I have an Openreach ECI modem and bought a spare (from the Kelly install engineer!) as a backup. The first thing ISPs often ask if you are troubleshooting a problem is to try an alternate modem/router.

    I’ve been reading that the ECI modem needs a firmware update before the line can use ‘G.INP’. Once the firmware has been automatically updated then the line would be updated. Again I’ve read (on Kitz) that to use a modem with the old firmware you would need a manual DLM reset so that the firmware could be updated before the line uses G.INP.

    I can see this presenting problems for people that keep a spare ECI modem as the firmware won’t be up to date and as far as I can tell won’t allow a successful session once the line upgrades to G.INP!

    If this is correct then it will effect people with spare ECI modems or people that buy them from eBay – and also people that use their own alternative modem/router most of the time but have kept the original as a fallback.

    If you can find out more information on this it would be useful.

    If BT hadn’t locked the ECI modem then people could check/update the firmware and avoid issues like this. It would also be a lot easier for people to troubleshoot FTTC lines if they were allow access to the line stats!!!

    1. Mark Jackson says:

      Trying to HmmmUK, but Openreach and BT in general have been very silent on the PR front today. Not even a peep in reply.. yet.

    2. Paul M says:

      This is very useful to know
      I have an Huawei, unlocked, with manufacturer’s firmware, as my main modem so I can get line stats off it.
      I bought a spare, just happened to be an ECI, cheapest available off eBay.
      Is your suggestion that I such to using my spare ASAP to ensure it gets a firmware update?

    3. Paul says:

      My answer would probably be yes, as it will currently see the HG612 as supporting G.INP and so won’t believe the device will need a firmware update prior to enabling G.INP at some point in the future (when DLM next needs to intervene and assign you to a retransmission profile). Unfortunately if the ECI is unlocked – I’m not sure if that will be updated automatically, I’m suspecting BT’s agent process was disabled to prevent the device re-locking itself again. I have an ECI /i and an ECI /r, both unlocked from the famous auction website, but I’m not sure if I’m going to end up with useless modem spares in the future.

  2. No Clue says:

    Well done to BT, i wonder if this is why yesterday morning after near 2 months DLM has finally got rid of the interleaving on my line (which has never been needed) and also given me back the 8Mb or so that i had been missing (something happened as ive never seen my line get adjusted at 10am in the morning, it normally happens after 6pm and more often than not around 4am).

    Whatever the case hopefully the changes work for the majority of people.

    Its nice to read something for a change where BT have/are trying to do something good rather than making excuses for not just getting things done or acting like a bunch of monkeys minus the bananas.

    Thumbs up to them from me, hope within days they do not go and do something stupid to and unrelated to balance out the good.

    1. GNewton says:

      You do realize that BT is heavily investing in the wrong yesterday’s technology, don’t you? To my knowledge you don’t have issues like signal losses or crosstalk noise on fibre lines.

    2. FibreFred says:

      The same wrong technology that lots of other countries are using around the world


    3. No Clue says:

      BTs DLM system is used around the world ???

  3. HmmmUK says:

    @No Clue
    I wonder if that was due to this change or another event?
    DLM type changes normally happen in the early hours with FTTC.

    Hopefully it was G.INP though as I’m also hoping it will improve things.
    I agree with you that it’s nice to read positive things from BT for a change!

    I spoke to a friendly Openreach engineer yesterday as he had his head in my local cabinet. He also confirmed that vectoring was being rolled out but could see my cabinet hadn’t been upgraded as there was a gap where the new card is fitted.

    1. No Clue says:

      Yep most of the BT monitoring/profile adjusting (or rather confused interfering granny as i call it 😉 ) for me normally happens around 4am, with it occasionally having a sniff at 6pm or 8pm in the evening.

      NEVER have seen it interject at 10am (ish) in the morning though and also while i was using the net. I may replace my current Openreach modem and find out for sure if G.INP is now enabled.

      I hope it is as it becomes tiresome when DLM can not make up its mind one month to the next. Why it changes things i dunno my connection never drops when its running at its fastest or gives any issues, but DLM will just randomly interfere, say “oi you.. here having some interleaving and a corresponding 8Mb(ish) speed decrease” LOL You then have to wait a month or two before poor old confused nanny monitor wakes up and puts it back to how it was. Hopefully that will be the end of it if this is G.INP.

    2. Paul says:

      @No Clue: I’m guessing G.INP is now enabled, hopefully it is anyway. I’d be interested to know if it really is, as I’m stuck on interleaving and feel G.INP would work better when it’s rolled out here.

  4. Matthew says:

    I would have hoped it would be more like ADSL where if the modem doesn’t support G.INP it still syncs just without the G.INP enabled.

  5. HmmmUK says:

    I’ve read (could be wrong) that an ECI modem with the old firmware will appear to be in sync (DSL light on) – but you can’t access the internet. The BT ‘fix’ is to perform a manual DLM reset to put things back to how they were and allow the firmware to download/update before reapplying the G.INP change.

    So not straight forward and a problem for people that like to have a fallback modem and also will make troubleshooting nearly impossible using an ECI modem.

    I’m reading this over on the Kitz forum, I’m not sure if ISPreview allow links?

    1. No Clue says:

      My modem is a ECI and the DLM/line profile definitely did not get reset before the change. I get the full 80Mb when that is done, I know that from experience and the 4 times my line has had a fault, ive had BT out to fix it where they reset line profiling/DLM after it completely borked itself. Also had the 80Mb on initial install of FTTC.

      Typically it then after a few days (call it a week) settles down to a figure in the 70’s. (suspect it makes a slight adjustment with regards to noise margin etc) Once it reaches the 72-75ish Mb range it typically sits in it will then normally stay like that for months on end and only drop to lower speeds if DLM has a mental fit and applies interleaving (which brings speeds down to the mid 60Mbps and basically as good as doubles latency to local sites).

      Im currently getting 73Mb and the interleaving is gone, IE line has gone back to how it will normally sit when stable. Whether it is due to G.INP i dunno yet but im hoping it is and with that it will stop DLM randomly dropping me to the 60Mb range every few months and then taking sometimes 3-4 weeks to put it back to the 70Mb range. Its like it can not decide if my line should or should not be interleaved, completely stupid system if you ask me.

      Its possible a new firmware was pushed to my ECI but i did not notice any down time when the adjustment got made at 10am a couple of days ago.

  6. Angel_Rex says:

    Good news indeed, I’m currently in SKY with the SR102 router. I have no idea how to check if G.INP has been enabled as these routers are locked down.

    Any suggestions?

  7. Paul says:

    Not sure on that one unfortunately.

    The DLM intervention time is odd, it used to be between 2am to 7am in the morning here, but recently it has been at other times (such as around 10am, and infact today a moment ago when upstream interleaving was removed it happened at around 11:30am~). I wonder what’s prompted the change in intervention time. G.INP still remains off however, I’m waiting for downstream interleaving to be reduced or removed given my ES+SES and resyncs are virtually non-existent. If DLM does however really consider the number FEC errors too then due to the ASUS reporting an abnormally high number of FEC errors I doubt it will reduce the downstream interleaving (INP/delay) :(.

    1. No Clue says:

      I think you will find DLM decisions are based on SES and ES and not FEC so while the Asus may have an issue reporting FEC figures correctly in its interface, theres no way its given people millions of FEC like i think i read on kitz a few months back… You connection would hardly work. I doubt that FEC will affect DLM. Depending on the Asus model, some of them do not show ES and SES figures so there will be no way for you to know your chances of getting or getting rid of interleaving.

    2. Paul says:

      @No Clue: I have access to TC, so I’m able to get detailed statistics from the device unlike the standard web UI which doesn’t show ES or SES annoyingly (and some other useful statistics such as INP and delay). The information I can get from TC is highly detailed.

    3. No Clue says:

      Does it still update stats correctly and match the figures from telnet and/or the devices web interface though? If its anything like Trendnet devices and additional busybox like apps you can only get accurate stats from one or the other.

  8. Phil says:

    G.INP is something Broadcom promoted as PhyR many years ago on ADSL, it is nothing new, it’s main aim was to improve things like video conferencing, IPTV and audio streaming which typically uses UDP which has no re-transmission mechanism. Overall it adds a delay of around 4ms, this is even for lines that have zero errors.

    G.INP doesn’t allow for sync speed increases, because if you increase the speed, errors increase also, and a chunk of bandwidth is then used up retransmitting, slowing things down. G.INP also doesn’t prevent noise destroying packets on the line, it just provides a way of re-transmitting them between modems, whereas interleaving does help prevent data corruption and makes the line more resilient.

    The benefit with G.INP for BT is it should reduce some traffic on their back-haul, as less TCP/IP packets will be requested in the higher network layers, plus it helps mask problems and avoids engineer call outs!

  9. Paul says:

    G.INP doesn’t increase sync speed in comparison to traditional interleaving (INP and delay being always in use)? Hmm, I thought G.INP is dynamically used (via bearer 1, not bearer 0) as and when a retransmission was needing to be done – so didn’t always make the connection suffer the loss of sync rate as you’d get with traditional interleaving.

    1. No Clue says:

      Indeed i also thought it either stopped errors or it did not, it does not “reduce” them or “G.INP also doesn’t prevent noise destroying packets on the line, it just provides a way of re-transmitting them between modems” it either works or doesnt its not a “inbetween” method.

  10. G.INP is designed to improve retransmission on “dirty” lines at the physical layer.
    Which allows the DLM and Modem to retransmit missed packets on a more “ad-hoc” basis. The result being that the line can generally sync a bit higher than before as occasional missed packet would get retransmitted.

  11. Thomas says:

    Let’s BP first concentrate on getting BT Infinity going in the areas where they advertise for in the tube stations. I have seen the ads at Queensway and Lancaster Gate station and yet unable to get FTTC/BT Infinity. They have been postponing it since I arrived in England in Early 2013. Now we are in 2015! England is still in the dark ages of broadband internet.

  12. Chris C says:

    Lets see some good journalism, why not report that its only a half baked rollout, with no ECI dslams? find out if and when EIC will get it.

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