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Standard User Andrue
(knowledge is power) Thu 11-Apr-13 19:44:59
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That weird thing called DLM


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My modem has been sitting at 71.2Mb/s for 34 days with SNR of between 5.6 and 5.3 and Max rate of around 70Mb/s. A tad naff for my supposed line length but it seemed happy enough. Error count was quite low.

This morning at 4am the connection was bounced and now I have this:

Max: Upstream rate = 26658 Kbps, Downstream rate = 77080 Kbps
Path: 0, Upstream rate = 20000 Kbps, Downstream rate = 65847 Kbps

With an interleaving of 1043.

My TBBQM suggests a single drop when interleaving was kicked on:

http://www.thinkbroadband.com/ping/share-large/565d1...

So it looks like at 4am the DLM woke up and decided to put interleaving on my line. Seems a bit odd to me :-/

---
Andrue Cope
Brackley, UK

Just because he could. RIP.
Standard User kasg
(fountain of knowledge) Thu 11-Apr-13 20:04:14
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Re: That weird thing called DLM


[re: Andrue] [link to this post]
 
In reply to a post by Andrue:
So it looks like at 4am the DLM woke up and decided to put interleaving on my line. Seems a bit odd to me :-/

It may be odd but it's not at all unusual - that's just what it does. It's happened to me several times, currently I have been without interleaving for over a month, the longest ever. It can't last!

Kevin

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Standard User jchamier
(knowledge is power) Thu 11-Apr-13 20:15:21
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Re: That weird thing called DLM


[re: Andrue] [link to this post]
 
In reply to a post by Andrue:
So it looks like at 4am the DLM woke up and decided to put interleaving on my line. Seems a bit odd to me :-/


I've never had my FTTC without interleaving!

James BT Infinity 2 19/09/2012 - Speeds 49 / 8.2 Mbps - Sync 53 / 9.5 Mbps @ 470m
Huawei modem -> RT-N66U -> Switch -> PC/Mac/Linux/NAS/Phone/TV - last speedtest
13 years of broadband - 1999 ntl:(512k/1M)/BTbusiness(2M)/Metronet(2M)/Bulldog(8M/16M)/BE(19M/16M)/BT FTTC(46M)


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Standard User Andrue
(knowledge is power) Thu 11-Apr-13 21:29:26
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Re: That weird thing called DLM


[re: kasg] [link to this post]
 
In reply to a post by kasg:
In reply to a post by Andrue:
So it looks like at 4am the DLM woke up and decided to put interleaving on my line. Seems a bit odd to me :-/

It may be odd but it's not at all unusual - that's just what it does. It's happened to me several times, currently I have been without interleaving for over a month, the longest ever. It can't last!
Yeah. I guess. I'm just puzzled why it suddenly took umbrage after holding nicely for over 30 days. A drop and reconnect at the full 6db margin and 70Mb/s would make sense but it seems a bit churlish to have stuck interleaving on.

And of then there's that weird change in max attainable rate. It did that a month or so ago after an engineer visit. It's like it's toying with me. 'Here, have some interleaving. Sorry it took 10% off your speed. But hey - it looks like you might get an even faster connection now if you wait a bit.'

:-/

---
Andrue Cope
Brackley, UK

Just because he could. RIP.
Standard User WWWombat
(fountain of knowledge) Thu 11-Apr-13 21:51:43
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Re: That weird thing called DLM


[re: Andrue] [link to this post]
 
In reply to a post by Andrue:
I'm just puzzled why it suddenly took umbrage after holding nicely for over 30 days. A drop and reconnect at the full 6db margin and 70Mb/s would make sense but it seems a bit churlish to have stuck interleaving on.

If you hadn't had any disconnections, then it is reacting to an increase in the error rate. Perhaps a small increase over a long period, or perhaps a few short but large bursts. They are enough to trigger DLM - which is aiming for pretty low error rates.

If it was a one-off, expect DLM to remove interleaving after 2-4 weeks. If it does so, expect the drop+resync to happen again in the 4AM-7AM region.
Sorry it took 10% off your speed. But hey - it looks like you might get an even faster connection now if you wait a bit.

It does look strange, doesn't it. The effect of interleaving does indeed seem to both drop the actual speed and increase the attainable value, while removal of interleaving does the opposite.

Perhaps it is a vagary of the formula used to calculate the max attainable (which is specified in the VDSL2 spec), or perhaps it is a bug in the modem firmware - either calculating the wrong thing, or calculating correctly but displaying the wrong parameter in the wrong place.
Standard User jchamier
(knowledge is power) Thu 11-Apr-13 23:20:31
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Re: That weird thing called DLM


[re: Andrue] [link to this post]
 
In reply to a post by Andrue:
Yeah. I guess. I'm just puzzled why it suddenly took umbrage after holding nicely for over 30 days. A drop and reconnect at the full 6db margin and 70Mb/s would make sense but it seems a bit churlish to have stuck interleaving on.

Maybe something made a TON of noise counters go through the roof at the DSLAM end and DLM noticed this and thought "uh-oh" and turned on interleaving.

And of then there's that weird change in max attainable rate. It did that a month or so ago after an engineer visit. It's like it's toying with me. 'Here, have some interleaving. Sorry it took 10% off your speed. But hey - it looks like you might get an even faster connection now if you wait a bit.'


I assumed my max attainable dropping from last Sept was due to other people taking up VDSL services, install was 19th Sept, so on 25th Sept I hacked modem, attainable was 59448kbps / 11957kbps and sync 49912/12065 - and today attainable is 61384/9493 and sync 52145/9496.

I assume attainable is without any error correction or interleave applied, and I assume for the attainable upload to reduce but the download increase means local interference profile has changed - not unsurprising given the weather changes. At install we had nice weather - then months of cold/frost etc, now its damp and +10C out there.

James BT Infinity 2 19/09/2012 - Speeds 49 / 8.2 Mbps - Sync 53 / 9.5 Mbps @ 470m
Huawei modem -> RT-N66U -> Switch -> PC/Mac/Linux/NAS/Phone/TV - last speedtest
13 years of broadband - 1999 ntl:(512k/1M)/BTbusiness(2M)/Metronet(2M)/Bulldog(8M/16M)/BE(19M/16M)/BT FTTC(46M)
Standard User Chrysalis
(legend) Fri 12-Apr-13 09:42:21
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Re: That weird thing called DLM


[re: Andrue] [link to this post]
 
my view is FTTC DLM is just plain sucks.

its more complex than ADSL DLM but that doesnt make it better.

I fast tracked mine back to fast path having a fritz 3370 plugged in for a few days as that on my line has extremely low error rates, even on fast path they were incredibly low compared to the hg modem.

I am not a fan of a DLM that drops sync to make a change when the line is otherwise stable. Also not a fan of one that cannot be overriden/turned off.

The attainable does go up with interleaving, although the actual sync goes down due to the FEC overheads.

BT Infinity 2 Since Dec 2012
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