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[MikeS]

Hi

I knew I shouldn't have posted a noise margin graph a few days ago

My line went pear shaped day before yesterday,  voice line crackly, dsl dropping.  Today BT came and switched pairs and cleaned up the voice line.  However I am now syncing now at 160K down and 320K up with what looks like a target margin of 9dB, despite the line attenuation having improved by 6dB.  For the last 8 weeks I have been syncing at 4000-4500 with an IP profile of 3000-3500 and a target SNR of 6.  Phoned Plusnet who said the reason was that because my line had been dropping and as I had been trying different routers the DSLAM had cut my sync rate, so I should leave my router on and wait three days and it should go up

My experience with noisy lines has been that the sync rate didn't change to this extent.  I may have gone from 4000 to 2000 during noisy periods. The method used to control downstream speed was to reduce the IP profile, which would go down to 250K in very noisy periods and maybe increase SNR margin.

I guess my question is -  is the sync rate determined by what the line can support, or does the DSLAM say 'despite the fact that the line can support higher speeds I am going to physically reduce sync speed because of recent poor performance' . By this I mean actually reduce sync speed directly rather than reducing IP profile or increasing SNR margin

Basically I don't want to waste three days at 160K if the Plusnet advice is wrong.  Any thought welcome

[roseway]

DSLAMs don't make executive decisions in that way. Your router negotiates with the DSLAM to get the highest speed which can be achieved for the target noise margin. This will depend on the attenuation and the amount of interference (noise). What are your current router stats?

[MikeS]

Stats are as shown below

Connection Status   Connected
Us Rate (Kbps)   320
Ds Rate (Kbps)   160
US Margin   6
DS Margin   9
Trained Modulation   ADSL_G.dmt
LOS Errors   0
DS Line Attenuation   48
US Line Attenuation   30
Peak Cell Rate   754 cells per sec
CRC Rx Fast   0
CRC Tx Fast   0
CRC Rx Interleaved   5
CRC Tx Interleaved   0
Path Mode   Interleaved
 
 
DSL Statistics
 Near End F4 Loop Back Count   0
Near End F5 Loop Back Count   0
 

My understanding was that the DSLAM/router negociated the highest sync speed for the line conditions.  The actual download speed would then be modified by the IP profile in place at the time, mine will almost certainly be rubbish due to the disconnections I have had.  If that is the case then waiting 3 days will be a waste of time.  Is there any way that switching pairs could confuse the DSLAM or does it look as if there is yet another fault somewhere.  I should say that I am coming directly out of the master socket and have tried 3 routers and three filters

I can't get on the BT speed tester to find my IP profile, but I would guess it is 250 ish.

[roseway]

On the face of it, those stats don't make any sense. You should get a much higher connection speed, in the region of what you had before. Waiting three days isn't going to make any difference - it's your actual connection speed which is the problem, not the IP profile. I think you're going to have to go back to PlusNet and make it clear that the connection speed is much too low, so the IP profile is never going to recover until this is fixed.

(I'm assuming that you haven't changed anything else at your end, and you're still using the same filters in the same places, etc.)

[MikeS]

Yes you are correct in terms of filters etc.  I'll have another go at them.  What I was told did not make sense to me, but I wanted to check it out with the experts before going back to Plusnet.

Thanks for the input Roseway

[roseway]

Good luck

[mr_chris]

Mike, Have you managed to make any progress on this? What did PlusNet say when you went back to them, out of interest?

Sounds like bad advice in the first instance there from PlusNet. Even if you didn't tell them the SNR was still at 6dB, the customer service bod should still have taken more notice of the extreme drop in sync rate, or they maybe didn't understand that you were referring to the sync rate rather than simply transfer rate (huge benefit of doubt given there, I know. I don't doubt that you made it clear it was your sync rate that had dropped!).

DSLAMs can, in extreme circumstances, drop your line sync to the equivalent of a fixed-rate connection, the telltale sign there is the upstream sync would fall to 288kbps there... like I say this is when your line is extremely unstable - and is known as a "chronic flapper" apparently

It sounds to me like you've got a major line problem, like you say in the post title! If it's still the same in the test socket behind the master faceplate, or at least with all extensions disconnected from the master socket, if possible, then it needs referring to BT. Just push your ticket back to Plusnet - it will get passed to BT soon enough... you could even include a link to this forum topic as I know a few of their staff do read this forum from time to time

[MikeS]

Hi Chris

I have pushed the issue back to Plusnet.  All I've got from them so far (a day ago) is -

Test result summary: Inconclusive

We have not been able to complete the checks of your broadband service. This may be the result of a fault in the testing system rather than your service

Not too helpful.  My experience with Plusnet is that once you get their attention they are very helpful,  however getting their attention takes time.  I'm feeling more than a bit frustrated as this issue arose due to a pair swop by BT, so I feel that it ought to get a bit of priority. 

The line seems stable.  Routerstats shows only very small 1dB blips in SN margin throughout the day/night.  The attenuation on the line is 6dB better than the old one.  I've tried 4 routers, only AR7 chipset routers will connect, my speedtouch's (510 & 546) will not connect.   

[Ezzer]

When you say pair swap, by any chance do you know if this was between say the exchange and cabinet/pcp/scp, or from the cab to dp (usually a pole)

Otherwise was it a pair change within a cable length between 2 joints ?

[MikeS]

The engineer said that the line was clear from the top of the road to the exchange but was noisy from the top of the road to the cab about 50 yds from my house.  So I assume he swapped pairs between two cabs at the top and bottom of my road - a pair change within a cable length between two joints (cabs)

[chrisparr]

Hi Mike,

I'd like to have a look at this and see who needs educating internally, and of course try to get to the bottom of your issues. Can you let me know your account name or a ticket number on there and I'll have a look.

[MikeS]

Hi Chris

The ticket number is ID: 24232031.  Just had a reply from the support team which seems to be a bit of a proforma job.  For me the issue was that immediately the pairs were swopped my sync went down to 160 from 3000+.  I'm coming out of the master socket via a face plate splitter directly to the router, nothing had changed my end in equipment terms before and after the swop.  I have since tried different routers/filters some won't connect (Speedtouch) but the DLink and SAR will but at only 160K

[Ezzer]

by cab thats the green box you sometimes see around (although some can be cable tv, mobiles, electricity, water), A 50 yard run sounds like a pair change from the cab to a joint (possibly an underground dp which feeds your property.)
This would be done if the fault causing the noise on your normal telephony can't be got at and probably mid cable lenght, thats when a good spare pair may be sought out to sort the problem. Ther's a chance that the pair you'r on now (although ok for now for normal telephony) could be effected by the same issue which effected the previous pair but is only brought out on your broadband. I which case the best route is raising this with your ISP so a broadband engineer to come out to look at another pair, but tested with broadband as well as pstn.

That's assuming there is a good spare, if not....That can poss be a whole new can of worms

[chrisparr]

Looking at your account we should be able to raise this to BT for investigation as the current sync rate is below the fault threshold rate they set for your line.
If you can reply to the ticket just to nudge it back in our direction (letting us know you've tried a different router, filter etc) I'll ensure one the speed fault analysts picks this up for you.

[MikeS]

Thanks for that Chris