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UPDATE BT Openreach Brief UK FTTC Fibre Broadband ISPs on G.INP Issues

Friday, April 24th, 2015 (4:18 pm) - Score 7,409
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Back in March we reported that BTOpenreach’s roll-out of Physical Retransmission ReTX (G.INP – ITU G.998.4) technology, which can improve the performance of their ‘up to’ 80Mbps capable Fibre-to-the-Cabinet (FTTC) lines, had hit a few snags (here) with some customers losing performance, connectivity and or suffering higher latency.

In simple terms, G.INP is an error correction solution that can help to tackle spikes / bursts of Electromagnetic Interference (impulse noise), which once enabled should make some problematic lines more stable and less prone to errors. Openreach completed the rollout of retransmission across their Huawei footprint / street cabinets (approx. 2.5m lines) on the 3rd April 2015, although they’ve yet to begin the roll-out for ECI cabs.

Broadly speaking many end-users can expect to see a benefit from G.INP, with most seeing their sync speeds improve and or lower network latency. But unfortunately this was not the same for everybody and some reported a spike in latency times, which was sometimes accompanied by a loss of speed. A few people even had trouble getting a connection after the upgrade was applied.

Part of the issue appeared to stem from consumers who were using VDSL2 modems and or routers that did not appear to include proper support for G.INP, which also impacted a few of Openreach’s ECI modems. In some cases ISPs have been able to work with customers in order to get the firmware update applied, but a few devices may still have problems and not all providers are as pro-active on this as they could be.

But today we have a few bits of new information, which come via way of a communication that Openreach has been sending out to ISPs. The document itself reveals some useful details and we’ve summarised those below.

Openreach G.INP Briefing to ISPs

* Retransmission can operate in both downstream and upstream channels simultaneously, although ECI equipment (either modems or DSLAMS) doesn’t currently support upstream retransmission.

* Any infrastructure that doesn’t support retransmission in the upstream will default to interleaving, increasing upstream latency by approx. 8ms.

g_inp_interleaving_fallback

* We have not yet started the rollout for the ECI infrastructure as we are investigating a minor issue with our hand held testers.

* Retransmission has so far demonstrated an improved performance over interleaving, resulting in a 6 fold improvement in error performance across the network.

* Retransmission has also had a positive impact on those lines supporting TV, with a greater proportion of lines now performing at less than 1 errored second per hour. There has also been a 15% increase in the number of lines able to receive a TV service.

* For the majority of lines, we have noticed a small (1-2Mbit/s) increase in line speeds, as a result of retransmission enabling the DLM to increase the headline rates. … Note that in some instances the available memory in the modem can limit the maximum headline rate, by a few Mbit/s, however this is quite rare.

* When retransmission is active on a line (retransmitting packets) latency naturally increases for a short period of time – but once retransmission stops the latency reduces.

The final part of the document focuses on what Openreach is doing to resolve the problem. “Openreach has recognised that the automatic application of interleaving in the upstream could be causing issues for some customers. We are investigating if we can deploy a change to remove the automatic application of interleaving in the upstream for those lines that do not need it. This will not impact the normal DLM processes, which may still apply retransmission / interleaving if the line requires it as was the case previously,” said the operator.

Apparently an update on their progress is due by the very end of this month.

UPDATE 27th April 2015

A trial to test the change mentioned almost directly above will not now begin for another two weeks.

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Mark Jackson
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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12 Responses
  1. Avatar John Elvin

    There is an error in your article. The DLM reset is for when a connection cannot be established at all using an ECI modem. Once the firmware update that triggers in done the user will be able to connect. It does NOT correct the loss of sync speed or the increase in latency. See http://forum.kitz.co.uk/index.php/topic,15283.msg284199.html#post_ECI_modem_issue1 for a description of the two separate issues for ECI modems.

  2. Avatar telecom engineer

    A DLM reset will remove all previous restrictions. An increase in sync rate may well be seen and improve latency although stability could reduce unless underlying issues have been resolved or dlm reinstigates its measures post analysis.

  3. Avatar telecom engineer

    Not calling you out that specific issue is incorrect all other things being equal but features of a reset are true regardless of retx.

  4. Avatar Tim

    Will we ever see FTTC increased to 100Mbps+ or will OR just use FTTdp (G.fast) as a way of making a new product, requiring a new modem and new contract?

  5. Avatar Kits

    FTTC isn’t all it is said to be since having this BT have systematical lowered my sync rate every time I had a performance issue. I have proof of sync of over 70Mbps when first moving to FTTC which lasted for months as the cabinet filled up throughput became an issue. After each openreach complaint on throughput they would say I wasn’t on a hot VP. On BT speedtester also would be good to see if others see the same thing upstream is capped on tap 3. Tap 1 can show 17Mbps tap 3 around 2Mbps only change is login details from my ISP to BT’s.

    These are things BT Openreach also need to deal with if my line was able to hold the 70Mbps at the start then cabling needs replacing to give those speeds back not lower what my line can give on BT’s ADSL checker.
    I have data to prove this which I feel needs bringing up at the next BT AGM if I can afford to go to London.

    This rollout increased my latency on the same gaming server from 14 to 28 the whole thing is a shambles..

    • Avatar MikeW

      Crosstalk is FTTC’s biggest problem. At least until a functional vectoring rollout, anyway.

      Crosstalk can reduce your speeds, and increase your error rate, unquestionably. From 70Mbps, you could lose perhaps 20Mbps to end up around 50Mbps; replacing cables won’t give you that speed back, nor will attending an AGM. Proof of initial speed is irrelevant … increased take up does have this effect, accumulating from day 1 until the cab is full.

      However, a drop to sub-20Mbps indicates either a fault, or severe congestion. That is worth pursuing. Just be clear about where you can expect a fix to take you back to.

      Meanwhile, the G.INP rollout has the potential to be very effective. But something has indeed gone pear-shaped for some users…

      If you care heavily about your latency, go get an HG612 modem, or swap to a combined router/modem that works well. The kitz site, from the first comment, is a good place to start.

    • Avatar DTMark

      High time OFCOM updated the Code of Practice as regards speeds to remove the three month limitation.

      Customer gets estimate on sign up which holds true throughout length of contract and can leave without penalty (here, in favour of VM cable, alt-net, 4G) for better performance without penalty if performance drops from that *initial* estimate.

      The technical inadequacies of congested VM loops or cross talk on VDSL lines should not be the customer’s problem.

  6. Avatar X5gb

    As well as Eci modems, I,ve noticed a lot of these articles fail to mention that it also affects Bt’s HH5a modem/routers as well. The HH5b is supposedly working with G-Inp.

  7. Avatar MrWhite

    I’m on a Huawei cabinet, but was given an ECI modem. I’ve noticed a reduction in connection speed – I’m assuming interleaving has been applied. Other than buying a Huawei modem, I’m assuming my only other option is to wait until BT roll out the changes to their ECI kit? Once updated, should everything return to normal?

    • Avatar Henri

      Plusnet do not give a bollocks atleast for me. They told me its to do with so-called line degradation and that they wouldn’t send a OR engineer to swap the modem. I originally got 81.6mbps and now I get 63.3mbps! And I get 34ms ping from my previous 12ms. Well, tbh it’s the contractor who gave me this kit in the first place…

  8. Avatar fingerbob69

    Well that trial is over and was successful… and the fix is being rolled out.

    See the post by SeanD BTCare Community Manager.
    https://community.bt.com/t5/BT-Infinity-Speed-Connection/G-INP-affecting-certain-eci-modems-resulting-in-a-drop-in-sync/td-p/1465234/page/37

    BT have so far though refused t give out any information in regards to their role out schedule when asked about specific exchanges.

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