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Author Topic: How long should I wait for DLM to remove interleaving?  (Read 3026 times)

Chrysalis

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Re: How long should I wait for DLM to remove interleaving?
« Reply #45 on: September 07, 2017, 07:30:45 PM »

yeah my install engineer does the same.
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Black Sheep

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Re: How long should I wait for DLM to remove interleaving?
« Reply #46 on: September 07, 2017, 07:46:02 PM »

Mr Cat is as always, correct. Just to confirm.  :)
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broadstairs

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Re: How long should I wait for DLM to remove interleaving?
« Reply #47 on: September 08, 2017, 09:51:54 AM »

I contacted my BT  person again yesterday and have heard back. It seems that despite changing the line profile to 80/20 DLM reset it back to 60Mbps again as well as turning on interleaving. They also reset the card but to no avail. Now they are sending an engineer to check to check out speeds at the cabinet. If this still fails to turn up what is wrong their next step is a lift and shift assuming there is a spare port. So it would seem that there is a problem somewhere in the part which BTOR are responsible for and TT's refusal to report my issue merely covers up a problem which does no one any good at all. I am not waiting to hear back from BT as to what is happening.

Stuart
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kitz

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Re: How long should I wait for DLM to remove interleaving?
« Reply #48 on: September 08, 2017, 10:32:01 AM »

Quote
It seems that despite changing the line profile to 80/20 DLM reset it back to 60Mbps again as well as turning on interleaving.

Im not sure about the 60Mbps cap as that isn't possible to see because the line is interleaved and interfering with your sync speed.  However, turning on interleaving again is not unexpected.   

What I am suspecting is that they have done a remote DLM reset.  I've noticed for a long time now (since ASSIA) that there appears to be 2 types of DLM reset.

- 1) Remote DLM reset - these never seem to clear any capping
- 2) Engineer DLM reset - a full line reset which will remove capping and start things afresh.  These can only be done by Openreach Engineers.

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WWWombat

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Re: How long should I wait for DLM to remove interleaving?
« Reply #49 on: September 08, 2017, 01:14:29 PM »

You're right Kitz, on two counts.... I had taken it to mean DLM in general, rather than wide-area events specifically. And I had forgotten the ASSIA impact.

I too think that the wide-area checking is a good move, in principle.

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skyeci

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Re: How long should I wait for DLM to remove interleaving?
« Reply #50 on: September 08, 2017, 01:41:46 PM »

I contacted my BT  person again yesterday and have heard back. It seems that despite changing the line profile to 80/20 DLM reset it back to 60Mbps again as well as turning on interleaving. They also reset the card but to no avail. Now they are sending an engineer to check to check out speeds at the cabinet. If this still fails to turn up what is wrong their next step is a lift and shift assuming there is a spare port. So it would seem that there is a problem somewhere in the part which BTOR are responsible for and TT's refusal to report my issue merely covers up a problem which does no one any good at all. I am not waiting to hear back from BT as to what is happening.

Stuart

Hi Stuart

You may recall my cab was not giving 80mb + at the cab ports when I had lots of issues with sync rates etc.. it was an eci too. In the end the engineer thought the  ports/cards were at fault as he could not get more than 65mb at the cab which meant a  further decrease at my house and regardless how many port swaps were tried they were all the same .A further pcr engineer deemed a physical wiring fault between cab and PCP which resulted in replacing the wiring loom on the eci cab... it only took me 4 months to get it fixed  :-\
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broadstairs

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Re: How long should I wait for DLM to remove interleaving?
« Reply #51 on: September 08, 2017, 03:16:09 PM »

I remember all your issues described on here.

I am waiting now for some feedback from my BT contact. I have had some downtime around 12:50-13-02 today when I guess something happened at the cabinet. I will update when I hear more. Depending on what BT say I may update TT with their findings especially if they report that there were issues at the cabinet. I think TT need to be more pro-active in reporting issues to BT where they have been long running things which should have been corrected earlier even if the line meets their (restricted) line speed estimates.

Stuart
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broadstairs

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Re: How long should I wait for DLM to remove interleaving?
« Reply #52 on: September 09, 2017, 05:49:05 PM »

DLM has intervened once again after the work yesterday. Is there any way to estimate how much speed one loses when interleaving is applied? This time I've lost some 7000kbps. I have not heard back from BT so I suspect this is as was suggested normal still annoying though.

Stuart
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lee111s

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Re: How long should I wait for DLM to remove interleaving?
« Reply #53 on: September 09, 2017, 05:51:17 PM »

I lost about 10meg.
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Ixel

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Re: How long should I wait for DLM to remove interleaving?
« Reply #54 on: September 09, 2017, 06:17:17 PM »

Depends on the INP, the higher it is then the more it'll take away. On my connection I've lost perhaps 1-2 megabits I think (downstream) when I get INP 3 with delay 8ms compared to fastpath. More delay gives a bit more speed and error resistance (though not as much resistance as applying INP too).
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WWWombat

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Re: How long should I wait for DLM to remove interleaving?
« Reply #55 on: September 10, 2017, 11:51:30 AM »

Is there any way to estimate how much speed one loses when interleaving is applied?

There are two factors...

The first takes away bandwidth, by using some of the bits as parity bits for the Forward Error Correction process. This tends to steal between 5% and 25% of the raw bandwidth...
- 5% is normal when G.INP retransmission is active
- 15-20% is normal for old-style interleaving intervention
- 25% is about the highest I've seen anywhere

You can see this from the framing parameters in the statistics. Parameter "R" shows the number of bytes being used as parity bytes, and the total block size is the "N" parameter.
(R/N)*100 gives you the percentage of bandwidth grabbed for FEC.

For example, mine are currently:
Quote
                        VDSL2 framing
                        Bearer 0
MSGc:           -6              26
B:              130             237
M:              1               1
T:              0               42
R:              8               16
S:              0.0518          0.3781
L:              21468           5374
D:              16              1
I:              139             127
N:              139             254
Q:              16              0
V:              14              0
RxQueue:                60              0
TxQueue:                20              0
G.INP Framing:          18              0
G.INP lookback:         20              0
RRC bits:               0               24

(8/139)*100 = 5.8%

The second factor comes from "coding gain". Because turning on FEC and interleaving increases the coding gain, the modem can try to carry more bits on each tone - because it knows that some of the errors are going to get corrected.

I don't know how to calculate this, but it seems to have two outcomes:
- On normal levels of old-style interleaving intervention, it gives you back about half of the bandwidth taken by the parity bits
- On G.INP retransmission intervention, it seems to increase the speed that the user experienced when on fastpath

Taking these two outcomes together, I think coding gain adds about 10% to bandwidth.

Combining both factors together, I think that these might be fair results:
- Old-style interleaving drops around 10% of speed
- New-style interleaving (as part of G.INP) adds around 5% of speed.
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Chrysalis

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Re: How long should I wait for DLM to remove interleaving?
« Reply #56 on: September 10, 2017, 12:03:38 PM »

wombat and kitz any comment on my opinion?
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kitz

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Re: How long should I wait for DLM to remove interleaving?
« Reply #57 on: September 10, 2017, 05:12:24 PM »

wombat and kitz any comment on my opinion?

I think it may be a personal preference.
 - Some people don't notice or mind the higher latency that comes with INP.
 - Others may prefer to lose a bit of speed rather than incur longer ping times.

>> I dont think a DLM that keeps flipping between 2 profiles is good,

In theory it shouldn't - each subsequent action should require a longer ILQ green status before DLM takes any backwards steps in order to prevent flapping profiles.

>> openreach want to maintain full control of DLM

They have probably made a rod for their own back with this approach.  I don't see why they couldn't give some control to the SPs.  There was talk a few years back that they were looking into it or considering it, but it all seems to have gone quiet. 

>> they know that DLM will 'mask' problems, so by removing DLM's actions then the problems become visible again and a net result will be higher fault reports.

Agreed - it masks certain faults quite well. Conversely some issues could perhaps be resolved with a reset.  The thing is there are some sensible ISPs, but some who would just push the button and hope that it fixes things.

>> how long people are expected to wait for g.inp is clearly way too excessive

Couldn't agree more.  As mentioned above with wombat, the whole DLM structure needs a rework.

>>  I dont know why openreach have done that config change as DLM wasnt like that at the start of g.inp rollout.

As mentioned, it was a botch job - a 'quick' fix to sort out the problem with the g.inp incompatible modems.  IMHO they vastly under-estimated the amount of users that had eci modems and HH5A's etc.

>>  I respect not everyone agrees with me there, and for that reason banding should not be permanent.

The problem is that it seems almost permanent and does cut in too soon.   People wait for months and nothing seems to shift even if the line has improved.
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WWWombat

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Re: How long should I wait for DLM to remove interleaving?
« Reply #58 on: September 10, 2017, 11:56:21 PM »

1. I don't think DLM (as we understand it today) should attempt to be a fast-response vehicle. It should be slow and considered, and leave the line profile in a suitable base state there the modem & DSLAM can handle the fast response themselves.

DLM, designed to run remote from the DSLAM, can never hope to scale up enough to cope with fast-response requirements on so many DSLAMs. IMHO (as a writer of scalable, robust, remote software), the Irish pun applies: "I wouldn't start from here".

Far better to use something like SRA, and/or FRA in G.Fast. Something running live, in the modems.

1a. Note too that I think DLM ought to mask problems with a line. Not forever, of course, but sometimes having a working line is better than one that only ever resyncs.

Perhaps it should keep you informed as to whether it has restricted a line below the fault threshold.

2. DLM also works to some strange requirements: to attempt to keep a line in a state where the end user sees no artifacts (visual/audio glitches on TV; almost no packet loss on data), but doesn't really get feedback from that source. The human end-user never gets to add their feedback to this loop, and it might be beneficial. No-one gets asked about whether you care.

Perhaps this is restricted to that latency vs speed option, or perhaps it just asks a question: do you see any problems?

3. Finally, DLM gets one thing wrong that wasn't obvious back when we first started with VDSL2: Its first action is always to change the line profile in some manner ... which kinda assumes that something is wrong with the current line profile.

Nowadays, as we encounter higher takeup and power/reset of the DSLAM, we get plenty of lines running on a low SNR because of crosstalk. Or lines that endure high ES rates because of the port's chipset.

In cases like these, the first step is a simple resync, to regain the target SNRM, and maybe reset the port. No need for any intervention more severe than that as step 1.
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broadstairs

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Re: How long should I wait for DLM to remove interleaving?
« Reply #59 on: September 14, 2017, 05:21:04 PM »

Getting back on track here a bit about my line.... The other day I had a call which was supposed to be TalkTalk asking me to call about an open complaint. Now because this caller sounded like someone from the Indian sub-continent I ignored it just like all the spam calls I have been getting. However having asked my contact in BT who was handling my issue whether they contacted TT the answer was yes! So it probably was a genuine call, oh well serves them right for having an Indian call centre, how am I supposed to know if the call was genuine or not as I had not got an open complaint with them as far as I knew.

Stuart
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