Kitz Forum
Broadband Related => Broadband Technology => Topic started by: roseway on May 18, 2010, 07:28:16 AM
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I've got involved in a discussion on the Zen forum, concerning the way in which DLM works with 21CN. Another member has stated that the BT Automatic Line Management System (ALMS) can increase the bRAS profile without the router having to reconnect at a higher speed. In fact he's stated (very firmly) that rebooting the router to get a higher connection speed is a very bad idea, and one should just leave it to ALMS to sort things out.
Before I make an idiot of myself by arguing about something I'm not really sure about, can anyone else throw some light on this subject?
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Hi Eric,
Whether or not it is a good or bad idea ALMS MUST be able to cope with disconnections effectively as there are many reasons for a router to re-boot e.g. Power cuts, BT Openreach work, user's misunderstandings etc. etc.
Kind regards,
Walter
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Yes Walter, there's no denying that.
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Another member has stated that the BT Automatic Line Management System (ALMS) can increase the bRAS profile without the router having to reconnect at a higher speed.
Could they be thinking of Seamless Rate Adaptation?
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Could they be thinking of Seamless Rate Adaptation?
That was what I thought at first, but reading the postings on the Zen forum that doesn't seem to be the case. The poster I referred to says that ALMS directly controls the connection speed as well as the IP profile, and another poster has said that his experience backs this up. I've searched in vain for any official description of how DLM works with 21CN, and the only reference I come up with is the discussion on the Zen forum. I wish I could get an authoritative statement from someone who really knows.
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Here's some info from PlusNet: http://community.plus.net/library/broadband/dynamic-line-management-dlm-on-adsl2/ (http://community.plus.net/library/broadband/dynamic-line-management-dlm-on-adsl2/).
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That's interesting, thanks orainsear.
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@ Eric et al,
Does anybody know if similar information is published by other LLU providers.
(Yet another subject for Kitz's splendid site !)
Kind regards,
Walter
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Hi Zoe,
Could I suggest you relax a bit !
These differences are minute and probably have no effect on your actual throughput speeds.
Assuming the CarPhoneWarehouse DLM operates in a similar way to BT's DLM it is unwise to reboot too often in any case.
It would also help us keep track of your adventures if you stick to your original thread.
Kind reagrds,
Walter
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Zoe, I have moved your two posts from here and put them with the rest of your "problem" in the ADSL Issues part of the forum under your original AOL New Contract heading.
This thread is more to do with a general discussion on a particular technology, rather than individual problems arising therefrom.
Hope you don't mind. :)
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Hi :)
Not sure if this relevant to the Topic: http://tinyurl.com/49k4zu So do feel free to remove it if it's not.
It's about how Sky Dynamic Line Management works :-\
Not sure if Sky runs of BTW or LLU.
But I do know that some LLU ISP's are now using DLM.
Zoe
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Thanks Zoe. It doesn't deal with the particular question I asked, but it still makes interesting reading. :)
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Too answer some questions...
The ALMS will perform similarly to SRA. However its not SRA. The banded profiles can be enabled at anytime and if the modem can cope, the line will adjust without a reset.
This gives the look and feel of SRA however allows the system to act more as an AI rather than adjusting to any issue/s that arises. Easiest wasy to explain is to say that the ALMS will learn from the lines profiles and noise levels and for lack of a better way to describe it, it will learn from its mistakes. The ALMS will adjust the profiles and the SNR targets down to 3db and upt 15db to gain the best possible speed. It can then add a profile of say 4-6mb effectively capping the line and allowing it to move between the 2 but not above nor below by more than a meg.
The system is still new and as far as I am aware BT are looking into implementing SRA alongside of this, however they are working on other systems to allow them to interface properly.
Hope this helps.
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Thanks Leo, that's very interesting.
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Thanks Leo, I'm fascinated.
However, this may (almost certainly) be due to ignorance on my part but...
if the modem can cope, the line will adjust without a reset.
How can the line be adjusted, without a reset, other than by SRA?
And regardless of the 'how', if we accept that it 'can', doesn't it render obsolete the concept of a 'target margin', since the target margin is simply the margin immediately after a reconnect, and there will be no reconnect?
- 7LM
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Hi 7LM,
Some modems can adjust the noise levels without resync'ing. The target Margin can be adjusted by the ALMS to assist in speed and line stability. On 21CN the ALMS will use a Target SNR of 3DB as a base for speed and then work upto 15db. Say you have a target SNR of of 6db and stable, the ALMS will then drop the target noise margin down to 3db allowing the modem to drop its noise margin. This does not require a reboot of the modem nor a reset.
With this in mind, the ALMS now has a lot more choices for stabilty and speed. Drop the SNR for speed, but then enable INP (Impuse Noise Protection) for stabilty.) Remove INP and up the SNR to 9db. Speed drops slightly but the latency is now lowered.
It all works together to try and maintain a balance. SRA will allow the same but in a different way, again adding more tools the ALMS' arsenal.
Leo
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, the ALMS will then drop the target noise margin down to 3db allowing the modem to drop its noise margin
Hmmm, I was about to question the concept of 'allowing a modem to drop margin', since modem's generally hang on to a connection regardless of variations in noise, as long as they can maintain sync with the DSLAM.
But, thinking further, are we saying that ALMS tells the modem to only allow the margin to drop so far, but to voluntarily reconnect if the margin falls below some ALMS-controlled threshold? From a quick look at G.992 (/G.997) I see that 'Minimum Noise Margin' is a defined parameter, and does indeed seem to support such behaviour.
If that's the case, then it would be interesting to see what happened if a user tried to 'tweak' the target. ALMS may decree (say) that the target is to be 12db, and the minimum is to be 6db. If a user then tweaks the 12dB margin down to circa 6dB, then every reconnect could be quickly followed by a 'low margin' event, triggering another reconnect, triggering another 'low margin' event, and so on... I do hope they've thought this through.
- 7LM
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... If a user then tweaks the 12dB margin down to circa 6dB, then every reconnect could be quickly followed by a 'low margin' event, triggering another reconnect, triggering another 'low margin' event, and so on... I do hope they've thought this through.
- 7LM
They have and this is why we ask our customers not to tweak the SNR as this can cause more problems than its worth.
Azz
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we ask our customers not to tweak the SNR as this can cause more problems than its worth.
A 'No Tweaking' rule would get my support, even with 'old' DLM (in most cases) though I'm aware that opinions vary :)
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Oh yes they do. In some cases it can help but in others in can cause issues.