Unexplained improvement in speed.

Discussion in 'Broadband' started by Steve Rogerson, Mar 19, 2012.

  1. I live at the end of a very long line from my exchange and suffer from outages
    and noise often caused by squirrels chewing the cables etc. Having said that
    when it is working I get a fairly constant about 900kb/s download speed and
    although it would be nice to get a higher rate I am not intending to move
    which is my only realistic option.

    Now I find that my speed has gone up to about 2Mb/s -or just over twice, which
    is good, but I don't know what's changed. I assume that someone fixed
    something at the exchange, but I can't find anything. Looking back through my
    logs I can see that the line dropped and I got reconnected with the higher
    speed at about 1:14AM on the 18th. There's something else that's odd and that
    is the SNR has dropped. I always believed that ADSL (+?) operated with an SNR
    of about 6, but historically I have always has an SNR of about 13-17. I've
    tried various tweaks to tease the line into giving a higher speed, but failed.
    At the same time as the speed went up, the SNR dropped to 6. It looks to me
    very much as though some equipment in the exchange has been replaced, given
    that my modem hasn't. Can anyone offer any insight?

    Steve Rogerson, Mar 19, 2012
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  2. That is one explanation. Another is that a bit of crap cable was
    replaced and a third is that someone fixed the sparking contact on some
    electrical equipment, or it blew up.

    Essentially the line now has less interference. There are many
    explanations and without any further information all are pissing in the

    Be grateful and shut up :) Or BT will come and take it away from you.
    The Natural Philosopher, Mar 19, 2012
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  3. Steve Rogerson

    Dave Saville Guest

    On Mon, 19 Mar 2012 17:03:00 UTC, The Natural Philosopher

    My speeds have improved following a two day outage due to "cable
    theft" :)
    Dave Saville, Mar 19, 2012
  4. You NAUGHTY boy. How much did you get for it?
    The Natural Philosopher, Mar 19, 2012
  5. Steve Rogerson

    Guest Guest

    His speed doubled and his SNR dropped by 9db, it is likely nothing changed
    other than the exchange not setting a 15db SNR target.

    It hints at a change of equipment at the exchange or it could just have
    been reset.
    Guest, Mar 19, 2012
  6. it doesn't say WHY the error rate dropped enough to warrant that target
    reduction though,.
    The Natural Philosopher, Mar 19, 2012
  7. Steve Rogerson

    Peter Able Guest

    Do you have a note of the Line Attenuation either side of the change?

    Peter Able, Mar 19, 2012
  8. Steve Rogerson

    Adam Guest

    My ADSL speed once doubled when I swapped the RJ11 cable.
    Adam, Mar 19, 2012

  9. 63.5 before and after. The same as now and - apart from outages - for all
    recorded time past.

    Steve Rogerson, Mar 20, 2012
  10. Steve Rogerson

    Peter Able Guest

    Sounds like the change is in the exchange equipment - either completely new
    equipment or a reset of the existing equipment - then. Your modem data
    might include the exchange equipment ID. I've found that I've needed a
    reset now and again to get back to a 6dB figure. They claim that an
    elevated figure eventually recovers. I've never seen it happen without a
    forced reset! Maybe Quantised Profiling will see an end to "stuck SNR

    BT changed the exchange equipment here a year ago and my connection shifted
    from 2 point something to 4 point something Megabits/sec sustained on the
    same 51dB line - and since we've been on QP I've always got an instant
    update of the IP and a 6dB margin after a router power-down then power-up.

    Peter Able, Mar 20, 2012
  11. getting 6dB on a 63dB loss line is very rare. a line that length would
    be expected to pick up the while MW spectrum. Id have expected it to be
    9-12dB margin ultimately.

    I wnet from a solid 3 and a bit to a flakey two and a bit, but after
    several BT openrteach visits ,is a reasonably clean five and a bit to
    six..BUT my attenuation changed as they gave me new copper.
    The Natural Philosopher, Mar 20, 2012
  12. I don't know what MW spectrum is, but as I said in my OP, to start with my SNR
    was about 15-17 db.

    I have just noticed something else my router ( draytek 2800VG) is reporting no
    corrected blocks in the ADSL Infomation section. Plenty of uncorrected blocks.
    This is not "normal", it has probably been happening since the 18th and I
    didn't notice. My understanding of this is that corrected blocks are blocks
    received in error, but the standard error correction stuff can fix - and
    uncorrected are ones in error but not correctable and need to be re-sent. The
    only way I can read the fact that the corrected block count has gone to 0 is
    that the CRC (or whatever it is called in this context) has been turned off.

    Steve Rogerson, Mar 20, 2012
  13. Steve Rogerson

    Mark Guest

    As your noise margin has dropped I'm not surprised if you error rate
    goes up. I suspect interleaving has also been turned off which could
    explain why you're not getting any corrected data.

    I would suggest checking this and ask your ISP to enable interleaving
    if this is currently off.
    Mark, Mar 20, 2012
  14. Steve Rogerson

    PeeGee Guest

    My line was running at 2500kbps, 3.5dB, 63dB attenuation and is now
    2850k, 2.5, 59.5 (for the last 200 hours). There doesn't appear to be a
    reliability problem.

    At one time, when the uplink was below 650k (it's now 731k) the line ran
    at 3000k/6/62.5


    "Nothing should be able to load itself onto a computer without the
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    to be removed from a computer easily."
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    PeeGee, Mar 20, 2012
  15. High. Long line?

    You might have been moved from ADSL to ADSL2+.
    Mike Tomlinson, Mar 20, 2012
  16. Long line.
    I don't think so. SamKnows says it is not enabled on my exchange. Also my ISP
    (demon) installs it's own equipment at to implement ADSL2+ and it's just too
    small for anyone let alone demon to bother with.

    Steve Rogerson, Mar 21, 2012
  17. Steve Rogerson

    Ian Guest

    I've not been following this thread closely, however...

    (I'd have thought that, with that attenuation, a change to ADSL2+ would
    make things worse rather than better)

    Some routers only report down to 63.5dB, so when they read 63.5 they
    actually mean "at least 63.5 - probably more". So it's possible that
    it was (say) 70dB before, and now it's only 65dB.
    Ian, Mar 21, 2012
  18. I don't think my error rate has gone up, though I don't have any hard stats to
    back that up. The surprise is the loss of "corrected blocks" of which there
    were previously many.

    I am not sure what "corrected blocks" have to with interleaving, but I am
    beginning to think that the change was to switch interleaving off. Why this
    would have been done without me prompting demon I have no idea.
    As I seem to be getting about 2x the speed I was before, I won't be doing that
    any time soon.

    Steve Rogerson, Mar 21, 2012
  19. the algorithms that BT use will make that happen automatically if they
    think you will get better overall response, anyway.

    All the symptoms suggest that a huge chunk of interference has gone off
    the line. But that is all. That could be a noisy DSLAM or a bad
    connections at the exchange.

    Enjoy it and dont fiddle.
    The Natural Philosopher, Mar 21, 2012
  20. Steve Rogerson

    Peter Able Guest

    Hi Steve,

    I haven't read anything that contradicts my previous ideas, but here is
    another possibility:

    I've a pal who has a line like yours, attenuation-wise, and he could never
    hold a fast connection with rate-adaptive DSL. Everytime he got a DSLAM
    reset executed it was a race between sudden disconnect and/or an upping of
    the SNR Target - with resultingly poor bandwidth. Then he got transfered
    onto a fixed rate 2Mbit/second service. Up went his sync speed (like
    yours), the SNR held steady and, although his throughput varied he got what
    he was after - a stable connection and a throughput up to about 1.7Mbit/sec.

    Is this the answer? Your ISP will know - and you might deduce it if your
    2Mbit/sec connection holds and your SNR doesn't get bumped up. Another test
    might be to try a disconnect/reconnect at, say, 8am and 8pm and compare the
    sync speeds!

    In the mean time, enjoy ;<}}

    Peter Able, Mar 21, 2012
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