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BT Wholesale "stability option" - had any luck/any experience?

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Weaver:
There's a lot of good stuff mentioned in that blurb (html doc has a date in it, dated end of september)
<blockquote>
Ability to choose

Currently, the link between the local telephone exchange and the end user’s premise is set for stability. That’s its default position. But now CPs have the ability to select one of three stability options depending on what their customers want.

For instance, more line stability is better for delivering video if the user is happy to forgo a little speed. In some circumstances choosing a higher stability option would be an obvious choice. For end users where lines are susceptible to 'dropping out' the super stable option offered by BT Wholesale may be the most appropriate. But speed can be unleashed on a line if a faster connection is more important.

All this fits into BT Wholesale’s aim to maximise end users’ broadband performance, improve service resilience and to deliver an exceptional end user experience. The broadband service provided by BT Wholesale is not one-size-fits-all. BT Wholesale is introducing a set of tools and techniques to push broadband boundaries to new limits. The stability options can be mixed and matched with other broadband tools [...]

The message is clear. It’s about flexibility - providing a service that meets the needs of end users and is tailored to their requirements. Stability options are part of the sophisticated broadband offering that highlights the progress made over recent years. They are available on today's broadband network - as well as the next generation broadband service being progressively rolled out across the UK. And it’s free for CPs to use."
</blockquote>
This is all good stuff. It's just what we need. But unfortunately it may be the case that ISPs don't know about it or are to lazy/disorganized to care or that BTW staff don't know their way around it or it may be that it's pre-announced vapourware.

sevenlayermuddle:

--- Quote from: Weaver on October 26, 2009, 11:33:21 AM ---Unfortunately it didn't last more than 48 hrs.

--- End quote ---

Weaver, 48 hours again!   That was exactly my experience, also with demon - but I suspect the ISP is irrelevant.  So often, when the target is manually over-riden by ISP request, it seems to revert back again.  And then BTw will refuse to override it a second time on the basis that there must be a good reason for it to have reverted.

Since BT won't publically document DLM all we can do is speculate, but one of my theories is that the designers of DLM may have included a tick box on the DLM control GUI to 'confirm all is well' after overriding the target margin.  If that box isn't ticked within 48 hours, the margin would revert.   It's just a theory but, if it were true, it would suggest that either BTw or the ISPs didn't know the proper procedure.

If it's any use to you, after waiting over a year for nothing to change I did recently manage to get my own margin reduced by CLI-tweaking to a massive positive margin.  After running with a 20dB margin for two weeks, the DLM target came down from 15dB to 12dB.  A few weeks later I tweaked back to 20dB again, and this time it got reduced to 9dB in just a week. .

Unlike the demon-initiated override, the target reduction obtained as above seems to have proven permanent - I now have a stable DLM target despite the occasional CRC error (~500 per day), and a sync speed of >4kbps on a 56dB line. But I can't guarantee the above wheeze will work for everybody, and you do need to brace yourself for apalling line speeds for a few weeks while the margin's up at 20dB.

Weaver:
> refuse to override it a second time on the basis that there must be a good reason for it to have reverted.

Indeed that's quite true. But the "reason" is wrt a _variable_ standard, according to service type. The point is that the error rate desired should be a parameter in the hands of the end-user, as per BTW's own blurb.

Indeed if the target SNR margin should be set far too low, so low that day-vs-nighttime and wet-vs-dry line conditions mean that there's simply too much variation, then indeed it's only to be expected that for some users a target SNRM set to 6dB is fine (because conditions don't change over time for that user) but for others SNRM will drop too far and a higher target is needed to allow for a future worst-case dip. Presumably a ridiculously and unrealistically high sync rate which means a very low SNR margin and very high error rate would end up with a situation where increased speed due to higher sync rate is more than cancelled out by retransmissions because of errored packets. (Where would the retransmissions be? Is there ARQ in the modem? Would you end up losing stuff at/above PPP? At/above IP, needing eg TCP retransmissions?)

My question to the ISP could be rephrased as "Is a business user slower than a non-business user?" (Because of low sync rate because of over-conservative DLM parameters.)

sevenlayermuddle:

--- Quote from: Weaver on October 26, 2009, 12:16:22 PM ---Indeed that's quite true. But the "reason" is wrt a _variable_ standard, according to service type.

--- End quote ---

I do understand service options, there was a thread some months ago on the topic and, at the time, I thought it seemed to explain my own experience.  However, I was making the point that I don't think that is always the explanation for DLM being unexpectedly harsh on some lines. 

In my case, my line - which had previously been deemed by DLM to be 'unstable' after an ISP-forced 9dB margin, later became perfectly stable with a 9dB margin simply through allowing DLM to do it's own thing, albeit with a little trickery on my part.  I never requested a change in service option, and I've no reason to think that it ever changed, hence I look for a different explanation...

Weaver:
My story was that I had been used to seeing

6dB SNRM on every DSL modem that
(i) is on a long line, well below the full whack 8128,
(ii) unless there's been a recent disruption, following which it should drift back to 6dB over time,
and where the service is
(iii) a home/homeoffice class DSL service - ie I assume IPStream Max not IPStream Max Premium) service.

And against this there is one long line that is on Demon Business and I assume therefore =IPStream Max Premium, which shows a constant longing for 9dB not 6dB, and is doing so because that's the default that comes with IPSTream Max Premium. Does that sound reasonable?

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