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[Jonnyteg]

10-11 meg is bob-on for your line attenuation, only way to squeeze a very small extra amount out of it would be to use a tweakable router and reduce your snrm to 3dB-ish, but you'd have to watch for stability if you did this :-)

I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor.   gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.


Your speed is good any way at 11 meg, much better than mine which is super tuned may i say  but a long line @ 4 meg with street average <2 meg.     

[kitz]

I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor.

If the line has been troublesome in the past, then I'd tend to agree with GJ and Johnny...  Id make sure the line was rock steady at 6dB before going any lower.

cant say i have ever seen one work well

@Jonny  - heres one for you for you to look at, just so you know it can happen    Pretty boring...  practically flat-lines at 3dB for the past 4+yrs.
(I do have a slight problem but its not SNRm related - more to do with a sloooooow deterioration of the line, but BToR would laugh their socks off if I called them out about it :/ )

[Jonnyteg]

do you not get any crc's with that 3db profile your sync speed is good    but 3db doesnt have enough difference for a reliable workplace or critical connection.   

Also the other thread on the thunderstorm affecting the fttc snr, have you noticed a dip on the snr during a thundersorm on your asdl2+ connection?

[kitz]

Nope, hardly any CRC's ever.  0 errors in the past 24hours.
Sync speed is Annex_M which means that I have given a chunk of my downstream tones to the upstream.   
4 yrs ago I used to be able to sync at 24/2.6, but over the past 3yrs the line has gone through a very slow decline.
If I wanted I could probably tweak the line down to 2dB and it would still hold - in fact I did that ages ago as an experiment and it was fine for several weeks.

>>have you noticed a dip on the snr during a thundersorm

Thats why I said "practically flat-lined".   
Thunderstorms are one of the few things that affect the SNRM and CRCs, but touchwood in all that time its never lost sync through one.   I did have some weird problems yesterday (link) but that sorted itself by tea-time, which is the only reason why RS is now running so I can see if it was just a one off - which it appears to have been. 

[Jonnyteg]

Nope, hardly any CRC's ever.  0 errors in the past 24hours.
Sync speed is Annex_M which means that I have given a chunk of my downstream tones to the upstream.   
4 yrs ago I used to be able to sync at 24/2.6, but over the past 3yrs the line has gone through a very slow decline.
If I wanted I could probably tweak the line down to 2dB and it would still hold - in fact I did that ages ago as an experiment and it was fine for several weeks.

>>have you noticed a dip on the snr during a thundersorm

Thats why I said "practically flat-lined".   
Thunderstorms are one of the few things that affect the SNRM and CRCs, but touchwood in all that time its never lost sync through one.   I did have some weird problems yesterday (link) but that sorted itself by tea-time, which is the only reason why RS is now running so I can see if it was just a one off - which it appears to have been.

You must stay in the exhange then    or next door why bother with fttc if your adsl2 is that solid?

[burakkucat]

My apologies to SlowConnector for perpetuating the hijack of his thread but I think it might be interesting to show the Sync Speed and SNRM graphs for my line so that the latter can be contrasted with that of Kitz, above.

According to the Beatie dbase, my line is 2481 metres from The Cattery to the exchange (EABSE). When I measured the distance, electronically with a Hawk, it was a maximum of 2164 metres (corrected for the test leads).

I am using an unlocked Huawei EchoLife HG612 as a modem/router to make use of its Broadcom 6368 chip. My CP is TalkTalk and the line is configured for a target SNRM of 6 dB with the DLM switched off. Having watched the 24 hour cycle of the SNRM for a number of weeks, I tweaked the DS target SNRM to 4 dB, thus gaining about 1000 kbps in DS Sync speed.

Like Kitz, I have a boring flat-line graph -- not for SNRM but for Sync speed! My typical SNRM graph is quite a mess -- see below. All said and done, I have been running like that for at least a couple of months without a single loss of Sync event. 

I wouldn't advise doing what I have done to the average end-user but being a techno-cat, I fully understand the consequences and the possible events that might occur. (If my SNRM graph was just that bit cleaner, I would have tried with a 3 dB target.    )

[GunJack]

I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor.   gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.

Sorry jonny, but you're off the mark there.... some points:-

1. yes, the initial snrm is set by TT profile, however using a DSL-2640B (6348 chipset) and DMT it is easily tweakable to almost anything you like.

2. TT LLU does not use any BRAS profiling

3. TT's DLM can be permanently disabled on your line if you ask, me and Mr. b*cat are testament to this.

4. my 50dB line is very stable, so I tweak down to 2.5dB peak in daylight, it troughs around 0.5-0.7dB in the small hours, for an extra 1000-1200kb/s sync. I don't get any loss of sync at those rates, yes I get several hundred CRC's in a 24-hr period but on a 64 depth Interleaved line it doesn't cause any problems.

5. I constantly get around 85% throughput, so no probs there.

On the above basis, hence why I suggested the  OP tried to tweak down for some extra speed if the line is stable enough to support it. There are many people who's line can support lower than 6dB snrm, but I suggest that the vast majority would never have understood let alone tried it, and forums such as this help spread the word

[roseway]

When I moved to BT-based ADSL2+ early this year, DLM quickly put me on a non-interleaved 3 dB profile, and it was stable for months in spite of the high error rate. So I agree with GJ that it depends on the particular line, but can be entirely satisfactory. Unfortunately in my case, a temporary intermittent line fault caused DLM to respond aggressively, but if this hadn't happened I'm sure I would still be quite happy with a 3 dB target SNRM.

[c6em]

My BT ADSL2+ line also runs quite happily at a 3dB downstream target interleaved at depth = 64 and always has ever since being converted to 21CN.
SNR margin trace is flat during the day  - the intial connection appears to always be around 3.3 to 3.5 rather than exactly 3.0
Line reported D/S Attenuation is 36.5, sync is usually around 13900 to 14100.
D/S margin drops to around 1.0 during the evening (always lowest curiously at 9.30pm) and yes the CRC errors do mount up overnight but then I'm asleep during that period!  I suppose if you do a lot of overnight downloading it might cause problems.
During the day although the FEC corrected errors are still accumulating the CRC's are pretty well zero so I can nearly achieve the IP setting during speed tests.
(Typical ping times from the command prompt are around the 28 to 30 mark with jitter being 1ms)

I did have a fault once which caused the DLM amongst other things to raise the target to 6.  Once the fault was cleared the DLM monitored the line for I think 2 days.........and promptly reduced the target back down to 3 again.

I have got a Routerstats trace somewhere of a thunderstorm going through where the CRC's and ES go bersek and the SNR margin drops to next to nothing/zero, line still holds in sync quite happily though actual throughput reduces to zero.  Once the thrunderstorm passed all reverted to normal.  No re-sync events, no drama etc.

So yes it does very much depend on the line and the quality of the house wiring and lack of external interfereces REIN,SHINE etc but quite possible to run at a 3db target continuously.

[kitz]

I think the general consensus is that if you know your line then 3dB can work quite well.  B*cats graphs show that hes well aware of the normal fluctuations of his line and by tweaking it hes been able to get the best speed whilst still maintaining a stable line.

The BTw DLM can sometimes be a bit of a pain when it kicks in, but since most LLU providers dont have DLMs that work in the same way as BTw's then those users can tweak with less caution than someone on a BTw based line.

I can see where youre coming from Jonny in that most users wouldnt have a clue how to get the best and optimise their lines, but the 3dB can and does work well for many.

Just FYI (I dont know if you are aware), but the reason why 6dB used to be the default goes back to legacy adsl when a minimum of 2 bits per tone was needed to load that particular subchannel during the sync up phase.  ADSL2,2+ only needs 1 bit.  Since each bit requires 3dB of SNR - adsl1 needs 6dB whilst adsl 2+ only needs 3dB to load the subchannel.

[Black Sheep]

Well, I never knew that Kitz. Keep feeding me please. 

[kitz]

Well, I never knew that Kitz. Keep feeding me please. 

yw BS..  theres a lil bit more info on the topic under bitloading. 
It should also be noted that the old fixed rate lines - ie true fixed rate 512/1Mb/2Mb and not capped rate rdsl which is used now - didnt utilise Target SNR Margins, which is why a longish line would either sync at a straight 2048kbps..  or it just wouldnt sync at all. 

[SlowConnector]

So far, the 6db profile seems to be rock steady, just like the 9db and 15db profiles, but I am still tempted to ask my ISP for the 3db profile just to see what the best connection for my line is.

Now that the source of RFI/REIN in my flat has gone away, the SNR does not seem to fluctuate at all. There was a thunderstorm in our area soon after I moved to the 9db profile, but it had no effect on the stability of my connection. The only thing I noticed was that the lightning registered as tiny ripples on my SNR graph.

Two things have supprised me so far: firstly the changes to my connection profile (15db then 9db then 6db) doesn't seem to have increased the sensitivity of line to line noise, as the connection has not dropped once. The SNR for my line has remained stable with each profile change.

Secondly, I am suprised how little gain in download speed has been achieved by changing profile. At 15db, I was getting a download speed of just under 8Mbps, and with the new profiles, it has improved, but not by huge amounts (9db gets 9Mbps, 6db gets 10.5 Mbps). Based on my experience to date, I am not sure there is going much gain from a 3db profile, but I will ask for it anyway.

Talktalk say that it is possible to achieve 30Mbps their ADSL2+ package if your line allows, but I think this is just bluster. It would be interesting to know what percentage of their subscribers actually achieve anywhere near this level of performance. My guess is that less than 1% of their subscribers get anywhere near 30Mbps.

[Jonnyteg]

I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor.   gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.

Sorry jonny, but you're off the mark there.... some points:-

1. yes, the initial snrm is set by TT profile, however using a DSL-2640B (6348 chipset) and DMT it is easily tweakable to almost anything you like.

2. TT LLU does not use any BRAS profiling

3. TT's DLM can be permanently disabled on your line if you ask, me and Mr. b*cat are testament to this.

4. my 50dB line is very stable, so I tweak down to 2.5dB peak in daylight, it troughs around 0.5-0.7dB in the small hours, for an extra 1000-1200kb/s sync. I don't get any loss of sync at those rates, yes I get several hundred CRC's in a 24-hr period but on a 64 depth Interleaved line it doesn't cause any problems.

5. I constantly get around 85% throughput, so no probs there.

On the above basis, hence why I suggested the  OP tried to tweak down for some extra speed if the line is stable enough to support it. There are many people who's line can support lower than 6dB snrm, but I suggest that the vast majority would never have understood let alone tried it, and forums such as this help spread the word

I was assuming a BTW circuit, thats great if you can tweak it to suit yourself although it seems like a lot of effort for little gains?

Yes the throughput should be roughly 85%, good put 82%

[kitz]

>>> doesn't seem to have increased the sensitivity of line to line noise,

The Target SNR(m) is basically a buffer zone to allow for fluctuations.
When graphing a line you would expect exactly the same fluctuations and blips and curves regardless if it was on a 6dB or 9dB profile.

Taking B*cats graph as an example, we can see that over the course of a standard day his line fluctuates between 5dB and 1dB = a 4dB daily variance.  If he had a 9dB profile, then the graph shape and fluctuations would be practically the same, only it would be graphed in the 10-6 dB region, rather than the current 5-1dB.

What you would expect to see however is that the error count on that line will increase the lower the buffer zone goes.  The more errors (CRC/HEC/ErrSec) you get then the more likely you are as an end user to see things like slower 'real time' speeds due to data having to be re-transmitted.  The nearer to 0dB you go, then the more errors will rack up..  including the more serious errors which will cause the line to drop completely. 


>> I am suprised how little gain in download speed has been achieved by changing profile

This is were attenuation comes into play.

Sync speed depends on the individual subchannels and bit loading during channel analysis at sync time.  Although we can say on average each 3dB of SNR is 800kbps, you have to bear in mind this is an average and the reality can be anywhere 400-1200kb. 

A 40dBm atten line isnt ever going to be able to load all of the adsl2+ subchannels available, therefore the effects of these profile changes will be far less than say someone with a 10dBm line who will be able to utilise all of the bins.  The less bins that are loaded, then the less effect it has on the sync speed.

Your line (40dB) is atm syncing at the high realms of its possibilities.

>> Talktalk say that it is possible to achieve 30Mbps their ADSL2+ package if your line allows, but I think this is just bluster.

Not only is that bluster, its technically impossible.  Even if your line was able to load every single bin with the maximum 15 bits, adsl2+ just does not have enough subchannels to support 30Mbps.  24Mbps is the limit. :/