Line attenuation and noise margin...

c0y0te

Hi folks,

I need someone to explain this to me please, and hopefully point me in the right direction for a solution.

Background:-

I've a 3mb down/ 384K up DSL connection (wired) using a Netgear DG834V3 (wired) modem connection via Magnet (originally Netsource). I've been getting reasonably regular disconnects and more recently the logs reporting "LCP Down" or "Initialise LCP fail" style messages.

I tried upgrading from a netgear V2 to a V3, ensured latest firmware in all cases and did all the usual support calls with Magnet. I even ran eircom to test the line etc. but to no avail.

I live in Malahide, not sure how far from the exchange but someone suggested the problem might in the quality of the signal from the exchange to my house and the line attenuation and noise margin info would indicate the quality.

So, from my router logs the following are the satistics:-

ADSL Link Downstream Upstream
Connection Speed 3072 kbps 384 kbps
Line Attenuation 32 db 9.5 db
Noise Margin 6 db 16 db

I've seen the noise margin (downstream) drop as low as 1db on occasion and rise as high as 8db. All the other stats seem to remain constant.

Could some kind soul possibly explain what the stats above are telling me and further whether or not it helps pin down the cause of my LCP drop issues? Thanks.

c0y0te

Ironleg

c0y0te wrote: »

Hi folks,

I need someone to explain this to me please, and hopefully point me in the right direction for a solution.

Background:-

I've a 3mb down/ 384K up DSL connection (wired) using a Netgear DG834V3 (wired) modem connection via Magnet (originally Netsource). I've been getting reasonably regular disconnects and more recently the logs reporting "LCP Down" or "Initialise LCP fail" style messages.

I tried upgrading from a netgear V2 to a V3, ensured latest firmware in all cases and did all the usual support calls with Magnet. I even ran eircom to test the line etc. but to no avail.

I live in Malahide, not sure how far from the exchange but someone suggested the problem might in the quality of the signal from the exchange to my house and the line attenuation and noise margin info would indicate the quality.

So, from my router logs the following are the satistics:-

ADSL Link Downstream Upstream
Connection Speed 3072 kbps 384 kbps
Line Attenuation 32 db 9.5 db
Noise Margin 6 db 16 db

I've seen the noise margin (downstream) drop as low as 1db on occasion and rise as high as 8db. All the other stats seem to remain constant.

Could some kind soul possibly explain what the stats above are telling me and further whether or not it helps pin down the cause of my LCP drop issues? Thanks.

c0y0te

Dude, your line attenuation is low which is good, you are about 2.4km (max speed 12MB) away from the exchange (dslam), some people would kill for attenuation like yours.
Your problem is low SNR Margin, you need to make sure you don't have any other equipment in the house connected to the line, try connecting your dsl modem directly to the main eircom socket without Splitter.
If that still doesn't help try another dsl modem or ring your Magnet customer support and tell them to increase Target SNR for your DSLAM if they are willing to do that.

dub45

http://www.kitz.co.uk/adsl/lowSNR.htm

http://www.kitz.co.uk/adsl/linestats.htm

Given that lots of people are bound to have problems when they upgrade their speeds in the near future would it be possible to incorporate those links into a sticky?

Praetorian

Hi c0y0te,

I have same 3m/bit connection.
Same ISP
Same modem more or less

My line stats are a bit stronger though

Connection Speed 3072 kbps 384 kbps
Line Attenuation 27 db 8.5 db
Noise Margin 16 db 14 db

I have an approx 15 metre cable running from the main socket to my DSL modem so I know I could get better Noise margin if I eliminated some or all of that cable. Less phone cable the better!

For about a month I kept getting disconnects, called tech support and they claimed no problem on their end. They reckoned someone was trying to use my name and password but I'm not convinced. Your attenuation is decent but the noise margin doesn't match it.

Have you got filters on your phone sockets?

Have you got sky or an alarm?

Try plugging in the modem into the first socket and plug everything else out.

If the first socket still shows the same problem, then there could be a problem on your line between the exchange and your house; some unusual interference some how

c0y0te

Thanks guys,

you have given me much to think about, and I forsee lots of testing ahead in an effort to eliminate possible microfilter/sky/telephone line problems

Praetorian - you bring up a very interesting point about the length of the telephone line from the socket. My dog ate through the last line so I went up to the usual DID/Harvy Norman crowd to get a replacement and they only had a 20m cable, so I bought that... but now I'm thinking I need a much smaller one if even to prove or disprove the difference.

Thanks again... I'll let you know how the testing goes.

Praetorian

I think that 20m cable is probably doing some of the damage. Might as well get it sorted since the upgrades are coming!

c0y0te

I've been testing this over the last few hours and here are the results so far:-

Average stats before I do anything (sampled at various times over 1 hour period) results is a downstream noisemargin moving between 3db and 12db, but settling down around 8db on average. Other figures remained pretty much constant.

I replaced the 20m telephone cable with a short one (ran it across the room) just to test the difference. The only thing I noticed was the it shifted around slightly less, but still averaged a noise margin on downstream of 8db

I then reseated/reconnected all the splitters/microfilters etc. and the noise margin settled down around 13db and remained pretty constant.

What is the ideal Noise Margin I should be looking to achieve here folks?

Also Praetorian - what upgrades are you talking about?

Sponge Bob

c0y0te wrote: »

Average stats before I do anything (sampled at various times over 1 hour period) results is a downstream noisemargin moving between 3db and 12db, but settling down around 8db on average. Other figures remained pretty much constant.

What is the ideal Noise Margin I should be looking to achieve here folks?

8 at least, ideally 10 or more.

Have you tried with no splitter , just the DSL straight into the wall socket !

6 is too little .

Snaga

The SNR margin isnt all that useful without knowing the speed you are syncing at aswell - and more importantly - if the sync speed changes as your SNR Margin changes (Which at those low SNR margin figures I would imagine is a fair bit).

Always provide these two pieces of information together.

Jonathan

c0y0te wrote: »

I live in Malahide, not sure how far from the exchange but someone suggested the problem might in the quality of the signal from the exchange to my house and the line attenuation and noise margin info would indicate the quality.

The exchange in Malahide is up beyond Scoil Iosa, about 700meters on the right hand side, when coming from the village. Almost opposite the turn for Portmarnock.

At present, I can't keep a connection for more than 90 seconds..

Constantly dropping, and re connecting. Can see the lights on the router lighting, stablising, blinking, and then turning off.

Incredibly frustrating, this is a new problem, and nothing has happened that I can think of to make this happen either.

Anyone got any ideas?

jackrussell007

Deleted User wrote: »

At present, I can't keep a connection for more than 90 seconds..

Constantly dropping, and re connecting. Can see the lights on the router lighting, stablising, blinking, and then turning off.

Incredibly frustrating, this is a new problem, and nothing has happened that I can think of to make this happen either.

Anyone got any ideas?

emmet I had that same problem recently with a DLink router I got from dell. I tried it in 3 different houses. Basically it would connect and then drop the connection with 90 seconds. Long story short, eircom said it wasnt their problem, they wouldnt support that modem. dell passed me onto dlink. I had two half hour conversations with their techies. upgraded firmware etc. told them I could connect with two other modems I had access to but couldnt keep a connection with the Dlink. for a finish I have sent it back to dell and have got eircom to send out a wireless router. at least they will have to stand over that, begin their line and their router.

for a finsh I'm not sure what the problem was. it was a pain in the ass though. hope I dont have the same **** again with this router

Praetorian

c0y0te wrote: »

I've been testing this over the last few hours and here are the results so far:-

Average stats before I do anything (sampled at various times over 1 hour period) results is a downstream noisemargin moving between 3db and 12db, but settling down around 8db on average. Other figures remained pretty much constant.

I replaced the 20m telephone cable with a short one (ran it across the room) just to test the difference. The only thing I noticed was the it shifted around slightly less, but still averaged a noise margin on downstream of 8db

I then reseated/reconnected all the splitters/microfilters etc. and the noise margin settled down around 13db and remained pretty constant.

What is the ideal Noise Margin I should be looking to achieve here folks?

Also Praetorian - what upgrades are you talking about?

Hi c0y0te,

Your connection is going to be upgraded to 7.6 m/bit in May / June. According to the line stat testers a solid 12/13 should be fine for that speed bump, but the more DB's you can grab the better (especially for further speed bumps into the future). The upload speed is almost being doubled as well, but I think your stats look fine for that.

Praetorian

Deleted User wrote: »

At present, I can't keep a connection for more than 90 seconds..

Constantly dropping, and re connecting. Can see the lights on the router lighting, stablising, blinking, and then turning off.

Incredibly frustrating, this is a new problem, and nothing has happened that I can think of to make this happen either.

Anyone got any ideas?

Emmet,

Try all the same things

"Have you got filters on your phone sockets?

Have you got sky or an alarm?

Try plugging in the modem into the first socket and plug everything else out.

If the first socket still shows the same problem, then there could be a problem on your line between the exchange and your house; some unusual interference some how "

Your line attenuation of 45 isn't terrible but isn't fantastic either. Sounds like you are a good bit away from the exchange, but you should be able to get a solid connection!

Yeah, we have filters on all phone sockets.

Eircom Phonewatch, but have had that for years at this stage. No Sky

Those stats were posted with the modem in the master socket, and nothing else connected..

c0y0te

OK, further testing/changes as follows:-

I replaced the long phone cable with a new 25ft one.
I replaced my phone handset with a new one.
I replaced the DSL splitter on the wall with a new one.
I replaced the phone cable to the wall with a new one.

Latest stats (on the same 3mb down/384K up) connection as I write are as follows:-

ADSL Link Downstream Upstream
Connection Speed 3072 kbps 384 kbps
Line Attenuation 33 db 9.5 db
Noise Margin 11 db 13 db

Stats seem pretty constant. I've got some further testing to do tomorrow (direct connect to wall rather than via DSL splitter, checking out all other connections etc.) to see if I can improve things even further, but from what you're saying these figures might be good enough for the upgrade.

btw - does this upgrade come at a price or do we all just get the lurverly bandwidth as a matter of course for the price we currently pay?

Praetorian

Free upgrades. I think the wholesale price might actually be cheaper but I doubt we'll see any savings. A good solid 11 db should be fine for the upgrade to ADSL2+ 7.6 m/bit.

Sponge Bob

He will get half the upgrade .

current 3072
atten 33
margin 11
new speed about 3500

http://www2.farina1.com/ADSL/default.aspx

TouchingVirus

Line State 	Up
Modulation 	DMT
Data Path 	Interleave

 
  	Downstream 	Upstream
Max Allowed Speed (kbps) 	3072 	384
SN Margin (dB) 	9.00 	18.00
Line Attenuation (dB) 	37.50 	21.50
CRC Errors 	48 	1

It's a new line (less than 3 weeks old) and only has BB for about a week now - are these stats good? I understand the attenuation is grand (well, grand enough) but apparently the SN Margin stats are low..

Praetorian

Sponge Bob wrote: »

He will get half the upgrade .

current 3072
atten 33
margin 11
new speed about 3500

http://www2.farina1.com/ADSL/default.aspx

I think the general consensus is that Eircom are using ADSL2+ so his max speed is likely to be 12 m/bit +.

Praetorian

TouchingVirus wrote: »

Line State 	Up
Modulation 	DMT
Data Path 	Interleave

 
  	Downstream 	Upstream
Max Allowed Speed (kbps) 	3072 	384
SN Margin (dB) 	9.00 	18.00
Line Attenuation (dB) 	37.50 	21.50
CRC Errors 	48 	1

It's a new line (less than 3 weeks old) and only has BB for about a week now - are these stats good? I understand the attenuation is grand (well, grand enough) but apparently the SN Margin stats are low..

Your getting a few errors downstream which indicates your connection isn't very solid. Try some of the advice above.

c0y0te

ADSL Link Downstream Upstream
Connection Speed 3072 kbps 384 kbps
Line Attenuation 33 db 9.5 db
Noise Margin 14 db 15 db


Regular views of my stats screen over the last couple of days have shown that things have stabilised down to the figures noted above. Thanks to all for your suggestions and feedback; hopefully the above will enable me to get even bettter bandwidth later in the year when this fabled upgrade kicks in.

I agree with the comments above though, perhaps a mod can extract a relevant summary from this thread and make it a sticky for others hitting the same sync/LCP issues?

My connection has now stabilised, for the time being anyway..
But my stats seem to have dropped severely!

DSL Status: Up
DSL Modulation Mode: GDMT
DSL Path Mode: INTERLEAVED
Downstream Rate: 2048 Kbps
Upstream Rate: 256 Kbps
Downstream Margin: 1 db
Upstream Margin: 15 db
Downstream Line Attenuation: 46
Upstream Line Attenuation: 30
Downstream Transmit Power: 0
Upstream Transmit Power: 0

Sponge Bob

Deleted User wrote: »

My connection has now stabilised, for the time being anyway..
But my stats seem to have dropped severely!

DSL Status: Up
DSL Modulation Mode: GDMT
DSL Path Mode: INTERLEAVED
Downstream Rate: 2048 Kbps
Upstream Rate: 256 Kbps

You have been downgraded to 2mbits, now go get yourself a refund.

Its the upload speed that proves it.

TouchingVirus

By dropping the sync speed shouldn't there be a corresponding increase in SNR?

ChessHacker

Router: Netgear DG834GT (Firrmware 1.02.09)
http://kbserver.netgear.com/products/DG834GT.asp

ADSL Link Downstream Upstream
Connection Speed 3072 kbps 384 kbps
Line Attenuation 43 db 13 db
Noise Margin 11 db 16 db

At night, my downstream noise margin will plummet and I get frequent
LCP disconnects, retrains, etc.
The connection becomes unusable.

However, a potential solution exists for Netgear DG series routers.
You can enable the debug login on the router by using the folllowing URL:

192.168.0.1/setup.cgi?todo=debug

This assumes that your router IP has not been changed from the default of 192.168.0.1.

Now you just open up a regular telnet session, which on windows you can do by:
Start --> Run --> telnet
A telnet session should then start.
You then type open 192.168.0.1 and away you go.

You can request your router fix the noise margin by using:
adslctl configure --snr 160 --sra on

where snr is the required dB * 16 and sra turns on "seamless rate adaption"

Examples:
# aim for higher SNR
adslctl configure --snr 200

# aim for lower SNR
adslctl configure --snr 50

# turn SRA on (use "on" to turn on)
adslctl configure --sra off

# reduce SNR and turn SRA off
adslctl configure --snr 200 --sra off

trant

Looks like an interesting tip, what setting did you use? I presume the best would be to aim for the higher SNR and turn SRA on?

ChessHacker

It's a life saver.

I use:
adslctl configure --snr 144 --sra on

to have a target of 9dB downstream.

It will sync lower than 3072 but it's stable.

You can also tweak the line modulation by using:
adslctl configure --mod [a|l|2|p|t]

The GPL source for this code is on Netgear's site.