cancel
Showing results for 
Search instead for 
Did you mean: 

Sync Speed Dropped And Won't Return

drbenway
Dabbler
Posts: 13
Registered: 21-01-2009

Sync Speed Dropped And Won't Return

Hi folks,
First, apologies for the lengthy nature of this. I want to include all the info I can! I've tried to separate out the questions for you Smiley
Some background: I became interested in how fast my router (Voyager 2100) was actually syncing to PN a month or so ago after reading through a few threads on this forum, and was shocked to learn that my sync speed was somewhere around the 750 mark on what I believe is BBYW Pro (up to 8Mbit). I restarted the router and lo and behold the sync speed shot up to about 5500. I can't remember the exact sequence of events but after some fiddling and restarting it sync'd at 1750ish, which I thought was strange so I restarted it again and got about 6240. This was about the highest speed I could attain, and plenty fast enough for now (after suffering through 750 anyway!). This is all plugged directly into the test socket.
First batch of questions, if you don't mind:
1a) Is it normal for the router to drop the sync speed over time?
1b) Is it normal to pick up wildly different sync speeds after restarting quickly in succession?
1c) (Following from 1a & 1b  Wink) Is my router knackered and in need of replacing?
All was well for a few weeks; consitent sync speed of 6240 and after a few days a matching IP profile of 5500. Lovely. In the meantime I'd developed an unnatural obsession with the sync speed of the router, and as such have my computer notify me of the current sync speed every 15 minutes, and log it.
On the morning of the 19th, however, it all turned sour. I went on the computer in the morning and noticed that the sync had dropped to a measly 1632 Sad Due to the logging, I know that this occurred sometime between 4am and 4.15am, which thanks to being kept awake by it I know was when it was chucking it down pretty heavily where I live. So, this raises the question:
2) Did the drop in sync speed occur due to the heavy rain?
I tried restarting the router, and experienced varying sync speeds, some a bit higher (2000ish) and one particularly lower (less than 1000). I eventually managed to get a sync speed of 5984 in the evening, after leaving the router turned off for the day. This held on until yesterday evening, when it dropped back down to 4608. A bit more meddling this evening (because I'm very bad at letting this go) and all I've managed to achieve is dropping to 4576.
My router stats as of just now:
[tt]
Line Mode    G.dmt      Line State      Show Time
Latency Type  Interleave  Line Up Time    00:01:11:09
Line Coding  Trellis On  Line Up Count  4

Statistics        Downstream      Upstream
Line Rate        4576            448
Noise Margin      14.1 dB        21.0 dB
Line Attenuation  38.0 dB        23.5 dB
Output Power      12.3 dBm        19.7 dBm
[/tt]
Obviously at this point my IP profile is shot to pieces, so that's no longer sacred and I'm willing to try anything, so one final question:
3) How, for my sanity, can I possibly get my old sync speed (or higher Wink) back?
I think I've got all the info in there, but now's the time to hit 'post' and wait for someone to ask for the obvious piece of missing information Smiley
Thanks for taking the time to read, you've been a great audience.
7 REPLIES
Community Veteran
Posts: 19,099
Thanks: 434
Fixes: 21
Registered: 31-08-2007

Re: Sync Speed Dropped And Won't Return

1a - No, except under fault conditions
1b - Yes, under fault conditions
1c - No, not necessarily, it could be a fault on your line or a faulty filter.
2 - Maybe. But wind could also cause the problem if any part of your line is overhead.
Stop rebooting your modem/router for the moment. Too many re-syncs in a short period, possibly five within an hour, will get your target Noise margin raised by the exchange and so lower your potential sync speed. It looks as though this may already have happened from those line stats. In general, a resync in daylight when noise levels tend to be lower will achieve the highest sync speed when there are no faults.
3 - It seems that you possibly have a line fault. Do the easy checks first. As you are plugged into the test socket, this has eliminated any internal wiring, extensions etc. If you have a DECT phone, turn it off, unplug it and replace it with a corded phone until the problems are resolved.
Listen to your phone line - can you hear any crackling or other intermittent noises or have you heard any recently. If yes, try another filter. If the noise still re-occurs, unplug the modem/router and check again. When the noise is present, phone your line rental provider faults (151 if BT), do not use any automated test, go straight to an adviser. Get them to confirm they can hear the noise and log it as intermittent. DONT mention the broadband (you will probably get the run around and referred back to the ISP).
Unfortunately noise from faulty joints/cable faults can disappear for a period when the phone is used or there is an incoming call (ringing current can clean the joint for a short while), so you may have to persists with such checks over a period.
If you do not have another filter to try (above), plug your corded phone straight into the test socket.
If the noise does not re-occur when the modem/router is unplugged, then borrow/try another modem/router to see if the sync problems re-occur. If they do, report a broadband fault to PN.
Edit: When listening to your line, dial a 1 to get rid of dial tone, if no obvious noise, you can do a full quiet line check, dial 17070 option2, but note comments above about disappearing noise.
drbenway
Dabbler
Posts: 13
Registered: 21-01-2009

Re: Sync Speed Dropped And Won't Return

Quote from: Anotherone
Stop rebooting your modem/router for the moment. Too many re-syncs in a short period, possibly five within an hour, will get your target Noise margin raised by the exchange and so lower your potential sync speed. It looks as though this may already have happened from those line stats.

Fair play, I will leave it alone for now. Would I expect to see sync speed increase of its own accord, or does this require a disconnect and reconnect of the ADSL line? If I need to manually re-sync, when will it be safe to give the router another kick?
Presumably if the target noise margin has been raised by the exchange this could be the reason I can't sync higher than 4576? Will the target noise margin decrease of its own accord in time?
Quote
Listen to your phone line - can you hear any crackling or other intermittent noises or have you heard any recently. If yes, try another filter.

There's no crackling on the line--a low level hiss, but nothing out of the ordinary. Certainly nothing I would call "new" Smiley
I did try another filter I have lying around, but this made no discernable difference. If it's useful I can change the filter back and post new stats, but presumably this will cause the router to re-sync.
Quote
If the noise does not re-occur when the modem/router is unplugged, then borrow/try another modem/router to see if the sync problems re-occur. If they do, report a broadband fault to PN.

I'll try and find a router I can borrow for a bit, to see if this makes any difference.
spock
Grafter
Posts: 29
Registered: 09-08-2007

Re: Sync Speed Dropped And Won't Return

Quote from: drbenway
Quote
Would I expect to see sync speed increase of its own accord, or does this require a disconnect and reconnect of the ADSL line? If I need to manually re-sync, when will it be safe to give the router another kick?


No, the sync speed will only change if you disconnect/reconnect the ADSL line or the line drops for some other reason. 
In my experience the odd resync will not cause a problem with BT's DLM system lowering the target margin as long as you remain in the same sync speed range and don't resync too often (say once or twice during the 14 day monitoring period - see below)
Quote from: drbenway
Quote
Presumably if the target noise margin has been raised by the exchange this could be the reason I can't sync higher than 4576? Will the target noise margin decrease of its own accord in time?


Yes, a raised target margin will generally cause lower sync, and as long as the line "appears" more stable to BT's DLM and your line is still on automatic DLM then the target margin will automatically reduce down by 3db at a time (min 6db).  This happens after approximately 14 days of stability (low error counts, sync's all within the same profile bracket). 
My line has been plagued by DLM so I have experienced a lot of this behaviour! 
Good luck with stablising your connection  Wink
Paul
drbenway
Dabbler
Posts: 13
Registered: 21-01-2009

Re: Sync Speed Dropped And Won't Return

Excellent, thanks for the advice chaps. I managed to use DMT to convince the exchange to drop the noise margin to 12dB, which means I'm syncing at 5696 (just on the threshold for a profile of 5000 Smiley). I have been trying to get it to reduce it further by restarting once a day, but it's not playing ball. However at least it's staying pretty constant now. Looks like I'll have to wait for a couple of weeks. A profile of 5000 is fine for now (already blown through my usage this month anyway), hopefully it'll go back up to the 6200 range when the noise margin reduces.
Is there a way to find out if the DLM is automatic or not? Or should I assume that if I don't know then it is? Smiley
Community Veteran
Posts: 19,099
Thanks: 434
Fixes: 21
Registered: 31-08-2007

Re: Sync Speed Dropped And Won't Return

Hi again,
DLM is fully automatic. Re-starting once a day will have no effect whatsoever on reducing the target SNRM. A long period of stability will. This may take longer than 14 days, it took 27 days for a line I know. Manual intervention by BT can change it, but they usually want evidence that the cause of the original problem has been fixed. If the target is lowered manually and problems re-occur, it can be difficult to get it done again.
In your case, the cause is not known, indeed there's no evidence yet that the line is stable.
If you are sucessfully using DMT, moving the slider to 50% forces the resync to occur 3db lower than the current target, moving the slider to 10% will get another 2.2dB reduction, so with a 15dB target the best you can get is 9.8dB. But a few words of caution using DMT. If a power dip or line issue causes a loss of sync then a resync will take place at the original target unless you can manually intervene with DMT. The fact that you may have DMT running and slider set will make no difference unless You press the Resync button. Unfortunately incidents like this only lengthen the period before DLM reduction in the target. Also, if you sync twice in, or for more than, 75 minutes in a lower speed band, your profile drops and will take 3 or so days to recover after you get the sync back up. I would start by setting the slider at 50%, resync during the day (not near sunrise/sunset) and monitor your SNRM for a while (several days).
DMT has a built in Noise plotter you can use (note - it locks out other functions whilst it is running). It can also hog a lot of memory on some machines, so if you are using your machine and need maximum resources it will slow things down. Best to leave it running when you're not doing much. Take a snapshot of a graph or 2 and post them here, along with some more ADSL router stats, one set of stats taken immediately after a resync.
Patience needs to overcome  frustration I'm afraid.
Regards.
drbenway
Dabbler
Posts: 13
Registered: 21-01-2009

Re: Sync Speed Dropped And Won't Return

Thanks again, Anotherone. My profile's raised to 5000 again, so I'm more than happy for now and willing to wait it out. I am convinced that the line is stable and the noise margin problems have been me being impatient, but as I say I will leave it for a couple of weeks and see what happens.
Am I right in thinking the best thing to do now is to watch the router stats for when the noise margin drops a few dB and re-sync then?
Superuser
Superuser
Posts: 9,126
Thanks: 535
Fixes: 46
Registered: 06-04-2007

Re: Sync Speed Dropped And Won't Return

Quote from: drbenway
Am I right in thinking the best thing to do now is to watch the router stats for when the noise margin drops a few dB and re-sync then?

If by "noise margin drops a few dB" you anticipate a change in target noise margin will immediately become visible - sadly it won't. The target noise margin can only be inferred by checking router stats straight after a re-sync; the noise margin at that time should be around the target level. But if you re-sync the DLM might feel your line is unstable, so not reduce the target noise margin. Rather a catch 22 situation. Sad.
The solution to this is patience, stay connected for over 2 weeks to convince the DLM that error rates are not large and that the line is stable. After this occasional re-syncing done carefully should be possible. Normally a router should tell the DLM that it is releasing the connection by user command - so the event doesn't get treated as a "line drop".A good approach is to switch off the router then wait 30 minutes or so before restarting. Doing this in daylight hours when noise levels are at their lowest will give the highest sync speed and remaining connected at this speed for a few days will help to provide the line-quality evidence that the DLM requires. A further switch-off, wait, restart cycle can then be carried out.
Hopefully, the DLM will be convinced and lower the target noise margin - which becomes evident when the noise margin immediately after restart has reduced (with sync speed correspondingly higher). Patience then for up to 5 days and the IP Profile should increase to the appropriate value for the higher sync speed.
Mission accomplished! Smiley
David