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[kitz]

Hot off the press -  news announced today!


With effect from next month IPStream & Datastream ISPs will be able to reset the SNR Margin on a customers line without having to report a fault direct to BTw.

CCSNR will be available to ISP's via the Eco system and will trigger a full retrain of the line.  This obviously means that not only will the SNRM be reset, but the line will go through a new 10 day training period including a new MSR and FTR calculation.

Some SFI faults which have been found to be a network issue, may also trigger what BT call an automatic SNR(M) reset.  It would appear though, that this will actually be a full line retrain.

However dont expect the ISPs to be too willing to do this without a valid reason, as the ISP has a strict limitation of how many resets they can request per day as the CCSNR system can only cope with a maximum of 3000 resets per days across the whole industry.  Any ISP abusing this facility could have their access withdrawn.

[roseway]

Great news! I'll be near the front of the queue.

[BritBrat]

I can see trouble ahead.

Do we relly trust offshore and ISP support to not just do a retrain when a customer contact them, yes some will be OK like Zen but I have no trust in a lot more.

[Chrysalis]

I see it triggers a MSR reset, which is a handy detterent put in by BTw.

3000 a day across a nationwide network, BT must be using very limited resources for profile management or they been very cautious.

[waltergmw]

I agree that this is very much a two edged sword. If I have struggled with Zen's invaluable help for two months and finally got a satisfactory resolution, I might be rather keen to get a line re-train.
However if there is, say, a high resistance fault on a line, maybe containing aluminium, the last thing anybody should want is to let BT O escape if the new MSR record shows a very poor performance.
If your ISP is effecient enough to keep a record of the line performance figures, there might be a mechansim to get BT O to re-visit a problem. However I wonder how many ISPs do actually keep those records and provide the data to the end user ? For those unaware I've included the data which can be made available on the 7 km line I've been helping with (and which has now been capped at 500 Kbps), although there is no guarantee that all data are included.

It will also be interesting to observe the retrain implications on lines that have been transferred to 21CN equipment.

Kind regards,
Walter

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[Azzaka]

We took part in the trial and found it can help some customers but of course not all. The reason we feel this is a good thing is due to the amount of chasing that would need to be done to have the MSR and FTR reset.

I have been chasing a line that had a low MTR and FTR and now that the line has been fixed we wanted it retrained. This was made easy bey the request.

I can appreciate a lot of the apprehention in peoples voices and I also do worry, however like all new toys it will need to be played with before we can find the limits. And BT have stipulated that they will withdraw support from the tool if it is abused.

[jeffbb]

Hi
Sounds OK as long as the ISP has suitably qualified people to know when to do the retrain. (I am OK  ). I can see where it might be applied by some of the less competent when a line fault still exists resulting in a lower MSR and FTR .No names no pack drill 

Regards Jeff

[sevenlayermuddle]

One scenario where I see this being very useful would be the when a consumer first gets DSL and is disappointed by performance and  then, a few weeks or months later, makes improvements like, say, a filtered faceplate, sorts out extension wiring or whatever.   It would indeed be nice if the MSR and FTR could then be reassessed after a new 10-day train.

However, the ISP would be unaware that such improvements had been made, so they would need to be acting on an end-users request.  Clearly, some good ISPs exist who may do so, but if your stuck with an Indian call-centre reading from a fixed script then I'm not so sure you'd get very far with such a request. 

Conversely, I can well imagine the call-centre scripts may be updated  to include a 10-day retrain as an attempt to 'fix' a line that's developed a fault.

All the more reason to choose a good ISP.

[Tirion]

We're currently trialling this at the moment, and my first request got chucked back. It would seem we're not able to actually specify the target SNR we want to be using, all it seems to do (from my initial experience) is reset the DLM.

I have a customer stuck on a 15dB SNR, that the Openreach engineer said "could be changed to 9dB" if we specifically asked for it.  Well, I did, and it hasn't been changed

If we do eventually get to hard-set a target SNR though, it could certainly make life easier for those tricky high-attenuation lines that perform poorly under DLM management.

[sevenlayermuddle]

Hi Tirion, and welcome.

If we do eventually get to hard-set a target SNR though, it could certainly make life easier for those tricky high-attenuation lines that perform poorly under DLM management.

I didn't think that's what was being suggested here.  As far as I understood, the target SNR will still be able to migrate up or down, dictated by the mysterious rules of DLM.  However, the new 10 day training period should have the effect of 'undoing' any historical accidents that led to an inappropriate target so, indirectly, it should 'fix' a 15dB target.

It should also have the effect of recalculating MSR and FTR.  If the new FTR turns out to be higher than before, it may in some circumstances discourage DLM from subsequently raising the target, as I think (can't be certain) that DLM is only supposed to raise the target if the sync speed is already more than 800kbps above FTR.   

Now a question...  I know that the 'default' target is supposed to be 6dB.  I don't know, and maybe somebody can clarify,  whether that means that the target is always 6dB at the end of the ten day period?  Or does the initial target vary depending upon performance during the ten days?

[Tirion]

The DLM process is a closely guarded secret it would seem

I have always assumed that 6dB was the target, but it's difficult to prove.  There's also the seperate issue of the IP profile, which doesn't always match the sync speed due to the FTR.

I have one at the moment that is in sync at 8Mbps, but stuck on the 500k profile.  Nightmare

[roseway]

There's also the seperate issue of the IP profile, which doesn't always match the sync speed due to the FTR.

I have one at the moment that is in sync at 8Mbps, but stuck on the 500k profile.  Nightmare

The IP profile hasn't got anything to do with the FTR. DLM is an automatic process, and will change the IP profile according to the connection speed. Reductions in IP profile are almost immediate after a fall in connection speed, but increases can take up to 5 days. What happens sometimes is that the IP profile gets stuck at a low level, even after the connection speed has been at a higher level for more than 5 days, in which case your ISP can get BT to unstick it.

[sevenlayermuddle]

[ DLM is an automatic process, and will change the IP profile

Eric, pedantically perhaps ...

It's my understanding that DLM doesn't change the IP profile, it just serves to stabilise a line that is perceived to have excessive error rates or to lose sync too often, by increasing the target margin and/or enabling interleaving.   In theory, but rarely perhaps in practice, DLM is also meant to reward a line that is 'very stable' by relaxing the margin and/or disabling interleaving, allowing better speeds or reduced latency.

The resulting connection speed, after DLM's intervention, is then taken as an input to the bRAS mechanism that controls the IP profile.

- 7LM

[roseway]

Well yes, you're right 7LM. DLM doesn't change the IP profile directly. The IP profile changes as a result of changes in the connection speed.

[Azzaka]

Well yes, you're right 7LM. DLM doesn't change the IP profile directly. The IP profile changes as a result of changes in the connection speed.

Unless its a 21CN circuit in which case it can change as a result of the changes made by DLM to limit it without the need of changing the connection speed.