Bad connection

[Rik]

Hi Dunkers

Everything is pointing at a BT-side issue at the moment, so once you've had a chance to do the MW walkabout, I'd suggest you get support to take a look at the line and see what they find.

For anyone interested, if you want your target margin pinned at a higher level to improve stability, just ask support, and they can get it done. I have mine at 9db because the line quality is poor.

[Simon]

Mine still seems to be pinned at 18db. 

[Rik]

Impossible, Simon, the highest official rate is 15db. If your router re-syncs at night, it will get a lower speed for the target margin than it will during the day. I currently have an 11db margin, which drops back to 9db at night, for example.

How stable is your connection, have you been able to hold the line for 14 days or more?

[Simon]

The connection seems to be stable, and here's what I can find:

Current Rate:         3776 kbs         448 kbs
Max Rate:       4912 kbs       836 kbs
Current Connection:
Current Noise Margin:       17.0 dB       18.0 dB
Current Attenuation:       34.8 dB       18.0 dB
Current Output Power:       19.5 dBm       12.1 dBm

[Rik]

Looks like you've only reached 11.5 days, Simon, hang one for another four or so, then re-boot.

[Simon]

OK, that was a manual reset, which I didn't think would have any negative effect.

[Rik]

Reset of the PPP session or a full re-boot. The latter would have counted.

[Sebby]

As Rik says, the last re-sync was about 11.5 days ago so give it another 4 to be on the safe side.

With regards to the 18dB margin, it must be 15dB. Remember that if the noise reduces since the sync, the SNRM will improve, regardless of the target.

[Simon]

Reset of the PPP session or a full re-boot. The latter would have counted.

No, it wasn't a full reboot.  Just a DSL Link reset.

With regards to the 18dB margin, it must be 15dB. Remember that if the noise reduces since the sync, the SNRM will improve, regardless of the target.

So, why does it say 18dB? 

[Sebby]

So, why does it say 18dB? 

Okay, so BT assign you a target of 15dB. You plug in your router and it negotiates with the exchange. What will happen is that the sync will be a figure such that the SNRM is 15dB. So your sync is going to depend on line conditions at that point in time.

Say you did that at night (the noisiest time). The next day, the noise will have reduced. So although your target remains unchanged, the actual SNRM can move either way after you have sync'd.

You could re-sync now and your new sync will be different to achieve a SNRM of 15dB. But then come tonight, you'll find that your SNRM will actually be lower than 15dB.

Don't try it though as you're trying to stay sync'd for 14 days.

[Gary]

Okay, so BT assign you a target of 15dB. You plug in your router and it negotiates with the exchange. What will happen is that the sync will be a figure such that the SNRM is 15dB. So your sync is going to depend on line conditions at that point in time.

Say you did that at night (the noisiest time). The next day, the noise will have reduced. So although your target remains unchanged, the actual SNRM can move either way after you have sync'd.

You could re-sync now and your new sync will be different to achieve a SNRM of 15dB. But then come tonight, you'll find that your SNRM will actually be lower than 15dB.

Don't try it though as you're trying to stay sync'd for 14 days.

which he cant as we have the engineering works this week unless that does not effect sync just ppp of course

[Rik]

I have a feeling it will drop PPP sessions, not sync, Gary, but that's just a guess.

[Gary]

I have a feeling it will drop PPP sessions, not sync, Gary, but that's just a guess.

I hope so Rik, if its been like the other lots of work done buy BT the it should be PPP, odd thing is I checked my exchange for listed work after my PPP session drop the other day and no work at my exchange was listed, saying that its probably just BT not giving the when and wears out for it correctly

[Rik]

Last year we were able to get a list of exchanges and dates. I haven't seen one this year.

[Gary]

Last year we were able to get a list of exchanges and dates. I haven't seen one this year.

BT probably can't guarantee their engineers will wake up in time from naps in from mobile phone black spots to complete the work

[Sebby]

[dunkers]

Thanks for the info peeps. I think I'll try having it pinned at 9db just to be sure that doesn't fix it (or maybe it does and that's job done!).

Er.. why would it be expected to get worse at night?

[Rik]

ADSL operates in the MW band, so at night, when radio waves travel further, there's more interference (the old Radio Luxembourg effect). As a result, you'll tend to see the noise margin drop during the hours of darkness and recover as it gets light. There is also an increased incidence from street and other lights.

[Gary]

There is more noise at night Dunkers, street lights etc can all cause line noise, it always dips at night time, I would honestly say that a sync of 4.5 is not bad for night as long as you go up to about 6db in the day which is your target, if you increase your snr by 3db you lose about 1MB on your sync rate for each 3db increase if I remember correctly

What Rik said 

[Mytheroo]

just to add, my mom's was 6db snr on 60db att. line, sync was lost every 2-30 minutes. Is now very stable at 15db snr target.

It all depends on the variance of noise I suppose, if noise bursts are 8db then u need 12-15db snr to survive the burst. If noise burst is 0.5db then you could probably sync with a 4.5 snr and survive it

[Gary]

just to add, my mom's was 6db snr on 60db att. line, sync was lost every 2-30 minutes. Is now very stable at 15db snr target.

It all depends on the variance of noise I suppose, if noise bursts are 8db then u need 12-15db snr to survive the burst. If noise burst is 0.5db then you could probably sync with a 4.5 snr and survive it

60db is a very long line though, Dunkers has an attenuation of 46db which is less than myself so I would have thought 4.5snr would be fine.

[Rik]

I agree with Myth, Gary - it depends on the noise. Because my line is prone to bursts, I have the target margin pinned at 9db to achieve stability. I could step up a profile if I had it at 6db, but I'd be forever re-synching (and probably dropping back the profile step I had gained).

[Gary]

I agree with Myth, Gary - it depends on the noise. Because my line is prone to bursts, I have the target margin pinned at 9db to achieve stability. I could step up a profile if I had it at 6db, but I'd be forever re-synching (and probably dropping back the profile step I had gained).

Its odd though that Dunkers has such noise on his line, but saying that it could be anything, living in the sticks does have some advantages it seems then, about the only one though, I just thought having such an attenuation of 46db he should not really have to have it pinned at 9db but of course environmental issues vary form place to place 

[Mytheroo]

The analogy I gave my Dad was, it's like building a tunnel to the exchange that you want to drive a car down, but you only have a set amount of bricks.

If the exchange is a long way away, then your tunnel has to be narrower, and you can't fit your Rolls Royce (8mbit) down it, you can just about fit an Astra (4mbit), and a Seicento (2mbit) fits fine.

Also, noise on the line is like the walls flexing in and out, so even though the Astra fits normally, occassionally the noise (flex) will trap the car and you lose sync, so you set the gap between car and tunnel to be higher (target SNR) and only try to send the Fiat.

[Gary]

I must admit its a great analogy, but you picked some awful cars, I have 4mb at 49db with a 6ish snr and its NOT an Astra being driven here