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[WWWombat]

http://forums.thinkbroadband.com/fibre/t/4473275-re-eci-fttc-cabinets-still-dont-support-ginp.html

Rumour - FTTC trial - making SNRM variable?

[kitz]

Ohhh nice find.   

It sounds like 3dB Target SNRm to me too.   

[kitz]

PS Off topic but something else I noticed in that same thread, re the HH5A not using G.INP.

According to Openreach's Chief Engineer both the ECI modem and HH5A performs retransmission in the downstream direction only.
I specifically asked about the ECI modems & HH5A's.  Ian surely would not have been prepared to put his name against something if it wasn't correct. - See Question 3 here
 
The whole reason I got something in print is because certain people were sceptical when I said the G.inp Mk1 issues were specific to the VRX-268 chipset in that it only supported downstream g.inp.  We had also been saying since Jan 2015 that if the modem couldnt at least partially support g.inp, then it wouldnt be able to connect to the Internet. BT rolled out f/w during 2014 to make the ECI modem g.inp compatible in the downstream direction. Unfortunately that fact was often misinterpreted too.

Ive no idea how we, as EU's can say if it is or not, because the HH5A doesn't give sufficient information from its stats. 

1) You cant use sync speeds as a base -  For example on my own line the VRX-268 chipset gives me 3Mbps less than the BCM6368 which in turn gives me 3.5Mbps less than one using a BCM63168.  It's a known fact that most lines will see speed differentials based on the type of chipset in use.

2) The 0.9669/0.9679% IPprofile method doesn't work for those routers performing downstream only g.inp.  We've proved this is the case for both ECI and Huawei cabs.

[S.Stephenson]

Question is does ECI get something first this time 

Seems great for lines like mine who's SNR only varies by 0.1dB, what are the odds of this rolling out in 2016?

Question is however will it be on only downstream on ECI and will Huawei be capable of this on both up and down?

[kitz]

Who knows with BT's trials

However, they are already aware of the fact that after application of G.INP, most lines run error free....  plus they know its already in use and working on ADSL2+ lines.

This isn't brand new technology, so if the trial is successful,  I can't foresee any reason why rollout should be delayed.

Question is however will it be on only downstream on ECI and will Huawei be capable of this on both up and down?

Its simply setting a configuration parameter, both types of cabs are capable of doing it both upstream and downstream, so highly unlikely it will be cab specific.   

I'm undecided how they will apply this.  IMHO the easiest way for them would be to make it like 21CN DLM as a param. But it entirely depends on how much they want to keep the speed cap.
 
1) They could replace the speed cap with a variable target SNRm and reserve capping for lines seeing high error levels.
OR
2) They could adjust the existing cap levels to fit 3dB.    Ive observed that rate limiting seems to more or less follow 6,9,12 dB, so that also would be fairly easy for them to do.


At one time BT were paranoid about users over-riding Target SNRm - they specifically saw (& cited)  DMT-tool as bad in their eyes, because it easily allowed users to play with SNRm... which is why they currently use rate limiting rather than a variable target SNRm.  So it depends if this is still a concern to them & if it is,  then I suspect they will go with option 2.

[kitz]

Its also worth citing wombats post here too.

old rule-of-thumb data I had calculated a year ago...

My rule of thumb for what an extra 3dB of noise margin is worth in the downstream direction:
- For speeds around 20Mbps, 3dB is worth 3Mbps
- For speeds around 40Mbps, 3dB is worth 6Mbps
- For speeds of 60Mbps or more, 3dB is worth 11Mbps.

The figures comes from using the 3dB to buy one extra bit on each tone. If that can happen across all downstream tones (about 2750 tones), it buys 11Mbps.

[S.Stephenson]

Just hope that we get to see a few real world examples when the trial starts 

Is there any charts that show the speed vs distance at 3dB on 17a?

[Chrysalis]

A guy on TBB who I assume has access to the BTw reports given to SP's has revealed its not long before some users will be part of a small (trial?) rollout of 3db SNRM.

Its logical to assume this will be on hauwei cabinets since they have had not very long to collect data on ECI lines.

[Bowdon]

A slightly off topic question.

What happens to SNR on FTTP? Does it exist, and if so is it higher than FTTC's SNR?

I'm assuming if there is SNR on FTTP then it would be higher. So when G.fast comes out, which could be seen as a hybrid between FTTC and FTTP i.e. bringng an FTTP line closer to the persons house, would this mean all our SNR stats will go up?

I guess my question is, are BT looking at SNR as they are looking for a new standard, 6dB being the FTTC standard.

Looking at WWWombat's figures in kitz post, imagine dropping the dB on a higher sync G.fast line, how many Mbps would that be worth?

[William Grimsley]

Really? Oh, yes baby! 40 Mbps here we come! We may all get a reset as well!

[William Grimsley]

So, I'm about to get a 3 dB SNR Margin? This is brilliant news! Any chance they can allow users to select the SNR Margin as well?

[plexy]

good news

though me wonders what the %age the threshold of line impact acceptability will be set at. Eg, if 1 in 10 trial users who are moved to 3db end up being switched back up to 6 due to issues, will that be an acceptable figure for general public use? BT have to think of support, tickets, complaints etc when speed drops from a high level to a lower level - even if that is a level that still within the service speed of the product. that would be perceived by users as a negative aspect of the product. I guess we will never know but lets hope that the results benefit us consumers in a positive way.

[William Grimsley]

Surely, the SNR Margin of 3 dB will only be enabled if DLM feels that the line is stable enough? Even if the 1 in 10 user gets the opportunity to experience the SNR Margin drop, DLM will only change it if the line is stable enough.

[roseway]

You're getting ahead of yourself, William. This is only a trial, and we don't know much about it yet.

[plexy]

The method of the switch isn't really relevant from a biz or consumer POV. The consumer will see drop in throughput, be it DLM or BT manually changing it. As part of the trial I think BT will be looking for how often those events happen. Most lines stable out eventually, though some stable out in a way that most of us folks in the know here would find unacceptable (the dreaded latency).

Look how much complaints crosstalk brought in - when it started to become a real issue and people saw their throughput dropping, the complaints started going up.

For the average user, the throughput dropping is nearly always noticed. If they have a service which does Xmbps and then later does less at Y mbps.

Sorry I'm probably being confusing, I'm going down into product viability and impact testing when really I should have the pom moms out and be cheering the fact the the sync on my line will rocket.

Now... if only BT did a service faster than 80/20.....