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ADSL2+ Line Training - Experiences and Advice

rengarth
Grafter
Posts: 31
Registered: 31-07-2007

ADSL2+ Line Training - Experiences and Advice

Hi,
My ADSL2+ trial started on 23 July 09. With the exception of one small blip on the same day, my modem's sync speed has varied between 15108kbps and 15941kbps. The "blip occurred on the same day as the trial started, and the sync speed then was 14301kbps. Furthermore, the modem seemed quite stable at 15537kbps from around 17:50 on 24 July until 08:45 on 26 July. No drops, no resyncs, and some very decent speeds. In all the above cases the up-speed had only really varied between 1075kbps  and 1259kbps. and the Noise Margin (SNR) was around 6 for both up and down.
This morning I woke to find that my modem had resync'd (not my doing, line simply dropped) at 12761kbps. Up speed 1221kbps with a down SNR of 12 and up SNR of 6.
I know this is only about Day 5 of the 10-day training period. I'm not asking anyone to actually DO anything about this.
I did read that sync speeds vary throughout the training period in order for BT to save bandwidth (I think I read that they prefer to set a line at a rate that has the minimum number of dropped packets, or something like that).
My question is this: After the training period, does the line settle at the LOWEST sync speed it attained throughout the training period (I read somewhere that it does), or is there a chance that the sync speed may increase again during the training period?
Additionally, things seemed to be going fine for me while my modem sync'd on the FASTPATH, though during the training period on 24 July the type changed to INTERLEAVE. While I was on ADSLMAX, my line settled on FASTPATH and remained that way with a permanent sync speed of 8192. Is there a chance that the training period will try FASTPATH again?
I repeat, I'm not asking anyone to DO anything about this, I'm just asking for advice. This ADSL2+ stuff is all new to me, and I guess is pretty new to a lot of people.
Thanks in advance,
Steve
14 REPLIES
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

Hi Steve,
The training period is designed to establish the best speed at which a stable connection can be achieved.  It is also the period in which the MSR (Maximum Stable Rate) and FTR (Fault Threshold Rate) are set.  The FTR is the speed at which any sync rate beneath is deemed an FTB (Fault Threshold Breach) fault, which can be raised to BT.
The MSR is set at the low end of the sync events during the training period but this does not mean that the connection speed will always be at that point.
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

IMO they should rename the 10 day 'Training Period'  as it there, as James has said, to establish the MSR and more importantly for the User the FTR. So it's important not to do anything with the setup that will cause a lower sync rate as this will lower the FTR. There probably been many examples where Users have keep rebooting their modems/routers trying to get a higher sync speed but instead have cause a higher SNRM and hence reduced the sync speed and FTR.
After the 10 days the line is still being monitoered and the system will change the SNRM and Interleaving, it can be hours, days or weeks between them depending on the history. I went from interleaved depth of 32 to Fastpath, to interleave depth of 120 to interleave of 16 in a matter of days after being on the trial for 2 months.
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

Quote from: itsme
There probably been many examples where Users have keep rebooting their modems/routers trying to get a higher sync speed but instead have cause a higher SNRM and hence reduced the sync speed and FTR.

The thing is, despite reading on a plusnet page . . .
http://www.plus.net/support/broadband/products/faqs_and_guides/dslmax_guide.shtml#Firstdays (Yes, I know that's about DSL MAX)
Quote
Whilst the testing is being carried out you should regularly make new connections to the Internet. It's a good idea to power off/on your modem or router when doing this, as this will force your equipment to reconnect.

. . . I haven't been rebooting myself. I only let the line resync when it drops itself. The way I figured it, the BT equipment might think that a manual reboot on my part would indicate a line drop, and consider it an unstable connection. So my modem is on 24/7. Always has been.
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

Bt will only consider it an unstable connection if there are 2 or more resynchronisation events in the space of 15 minutes.
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

So does that mean you suggest that it could be a good idea to reboot a modem or router, say, every few hours during the training period, James?
(By the way, James, I've not yet thanked you for all the help you've given me over the trial so far. "Thank you" seems a little inadequate, to be honest!  Smiley )
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

You've thanked me a number of times actually!  I'm really just doing my job Smiley
I'd just stick to a daily reboot first thing every morning.
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

Well in that case, thanks AGAIN, James  Smiley
Not sure how useful these figures would be to you (or to anyone else), but I've attached a PDF of a spreadsheet I've been keeping since the Trial began. It comprises router figures, speed tests from two separate sites, and the occasional speed test from the BT speed tester.
grahamt
Rising Star
Posts: 552
Thanks: 10
Registered: 05-04-2008

Re: ADSL2+ Line Training - Experiences and Advice

Very interesting figures. As someone with an attenuation figure slightly less than yours (39dB) but an ADSL2+ downstream sync that's never got higher than 5200 (and currently limited by BT banding to 3069, which gives me a BRAS profile of 2500 and a real throughput of around 2.3mb/s) I'm green with envy.
However, some people have seen quite big (negative) changes after a month or two of being on ADSL2+, so you can't rely on a stable sync even after your nominal 10-day training period has ended. The DLMs don't always seem to work in the way they're supposed to. But I hope your experience stays good.
Graham
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

Oh I'm aware of other people's experiences, Graham. That's why I intend to keep the figures going well after the training period. So if there IS a drop in sync speed in a month or so, the stats might help to reinforce arguments and questions as to why this happens.
One question that DOES come to my mind, though, is that I've seen many posts on here from people on the trial who have suffered drops in sync speed, but I'm wondering if this is a representation of everyone on the trial, or just those who are having problems? I'm wondering of there are others on the trial who have had good speeds and a good experience throughout, who simply see no reason to comment on it because things are going so well for them?
Personally I feel it would be good to get a broader representation of those on the trial, so that things may be identified that WOULD contribute to a lower sync speed, either initially, or after a longer period of time. Line length, atmospheric changes and such can't be the ONLY variables.
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

Wish I kept a detailed record like that. I have got records of the sync speed being logged every hour but thats only half of the story. My only suggestion is to record the interleave depth as you will see this change when the DLM is in an active mood. With my connection it reduced the SNRM from 15dB to 6dB but increased the interleave depth from 16 to 120. At the time I thought that 32 was the highest.
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

Unfortunately my router doesn't record or monitor the interleave depth.
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: ADSL2+ Line Training - Experiences and Advice

It's normally just shown as D in the stats. and typical values will be 16 down and 4 up.
rengarth
Grafter
Posts: 31
Registered: 31-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

These are the only stats the router reports:
Community Veteran
Posts: 6,419
Thanks: 531
Fixes: 48
Registered: 30-07-2007

Re: ADSL2+ Line Training - Experiences and Advice

I presume from the piccy that its a Belkin F5D8631 , have you tried to see if that model has any of the hidden Belkin pages http://www.kitz.co.uk/routers/belkin_commands.htm ( make sure you have the right IP address for your router when using those commands ).