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Would you say I have a line fault?

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Would you say I have a line fault?

Hi looking at my SNR on the router I have:

Downstream: 11 dB
Upstream: 27 dB

Now I only live approx 150 mtrs from the exchange and if I really tried could probabaly hit it with my now obsolete FREE Evil usb modem from Plusnet.(which although free will cost me £25 if I dare transfer out).
Anyway back to the point.
Would you say that I should be getting a much better Rx SNR than 11 dB.
The telephone junction box that feeds my street is just outside and I would think is the only "joint" between me and the exchange and to get such a low SNR over 150mtrs cable seems poor.
I have tried the "removing the lower face plate" from the main phone socket and plugging the router in direct to bypass the internal extension wiring etc.. but still remains at 11dB.
Any thoughts welcome..

PS: anybody wanna cheap usb modem..(well looked after.. never been thrown Wink )
10 REPLIES
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Would you say I have a line fault?

No thats probably correct for MaxDSL. (assuming you are on that)
the loss of the line inreases quickly with distance but signal to noise ratio is very much dependant on which frequencies and which how wide a spectrum they cover.
(I should have used the word bandwidth for spectrum but IT industry has stolen and misused that word to mean something diferent now)

Anyway back to the issue. your upstream i.e. the signal sent by you do not cover such a wide range and have a higher SNR figure.
Whereas the downstrem i.e. signals received by you cover 8mB which is a much wider spread and so you see the lower figure even though you are close to the exchange.
N/A

Would you say I have a line fault?

Your right I have just switched to MaxDSL and havent got pre MaxDSL figures to compare with.
My speed has always been pretty good (std 2mbps)its just after reading a few posts thought I would check my SNR and saw it was so low..
I knew that after the first 10 - 14 days then my speed would be set so I thought with such a low figure then I would not be any better off (speed wise)
At the mo` I am getting about 3-4 Mbps just hoped I would have got closer to full speed being so close to the exchange.

Thanks for the reply.. much appreciated..
N/A

Would you say I have a line fault?

Line attenuation figures? Sync speed?
N/A

Would you say I have a line fault?

Quote
Line attenuation figures? Sync speed?


oops sorry..

usually very close to these figures.

shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Would you say I have a line fault?

Your line length would appear to be about 350 metres yet your SNR is worse than mine at 2 Km-- I'm a little surprised that you're not synching at 8128 Kbps though and that your connection is interleaved since it ought to be pretty stable unless whatever has pushed the SNR down is messing things up
N/A

Would you say I have a line fault?

Hi Shellsong thanks for the info.
How the heck did you work out my line length :shock: ?
I guess the wiring must go here there and everywhere before it gets to me as it is def approx 150 mtrs as the crow flies, which is at high altitude round here as the little sods who dwell in caves locally dun like crows.
Are you on maxdsl?
As JohnEssex pointed out to me and I think I understand his point.. because maxdsl uses a wider bandwidth therefore the ratio between signal/noise will always be worse.
If you are on maxdsl could you please give me your figures so that I can compare.
Thanks..
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Would you say I have a line fault?

Rough rule of thumb is 14dB downstream attenuation per Km! There, I've given the game away-- noone will recognise my genius any more! Tongue :lol:

These are my present stats for what it's worth

ADSL Status
Item Status
Showtime Firmware Version: 3.52
Line State: SHOWTIME
Modulation: G.dmt
Annex Mode: ANNEX_A
Startup Attempts: 25
Max Tx Power: -38 dBm/Hz
CO Vendor: ALCATEL_NETWORK
Elapsed Time: 19 days 21 hours 38 minutes 25 seconds

Item Downstream Upstream
SNR Margin 11.5 25.0 dB
Line Attenuation 29.1 20.0 dB
Errored Seconds 2817 4
Loss of Signal 24 24
Loss of Frame 0 0
CRC Errors 1347 0
Data Rate 8128 448 kbps
Latency FAST FAST

It's giving me the lie-- my SNR was about 13dB! Honest! :lol:
I've not done anything about trying to improve my SNR by plugging into the master socket direct or fiddling with me extensions though (they can't touch you for it I'm told! Tongue )
N/A

Would you say I have a line fault?

Hi just found this useful site:
http://www.kitz.co.uk/adsl/linestats.htm
Now if I read it correctly then I`m reading the router wrong!

My router and yours ShellSong is showing SNR "margin" which is the differance between what SNR you need and what SNR you actually have !
So that means I`m getting the minimum SNR for my speed PLUS 11dB !!

Taken from that site:
"The SNR Margin is the difference between the actual SNR and the SNR required to run at a given speed.
For example, if you need 20dB of SNR to run at 512Kbps, and the actual line SNR is 45dB, then the SNR Margin is 25dB."

Also it would appear that the maximum SNR margin on maxdsl is 15 dB..

"With Max a target SNR margin is set on the DSLAM and its your router and the DSLAM that agree the best way of meeting this target margin. The target margin range is between 3dB and 15dB and rises in 3dB increments - although it is normal for it to fluctuate either side during the training period.
The default is 6dB without interleaving."

But I still dont understand why I am on "interleaving" when my snr margin is just 1 step below max (3db steps)

Now because my best speed is decided between the router and the dslam should I change my router? as it is not the best about..
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

Would you say I have a line fault?

I'm not sure what that kittz quote about SNR Margin is actually saying although I reckon she knows a darn sight more about these things than I am likely to know

My understanding is that what our routers show as "SNR Margin" is what they measure as the ratio of the signal level above the line noise level although I can well believe that some people might reckon the "margin" should be the level in dB above the lowest level that a reliable signal can be discriminated

Normally with ADSL BT used to allow a minimum margin of 10 dB before they would allow a customer to be placed on a given speed rating but with MaxDSL the equipment is (theoretically) allowed to adjust the rate until a nominal SNR figure is achieved (default about 6 dB)-- this can be modified if there are problems

So you see you and I have about 5 dB to play with at present, which is equivalent to being able to nearly double the synch rate

One thing people who've been placed on the Tiscali LLU have been finding is that Tiscali in their infinite wisdom have chosen a margin of about 12-15 dB as their target! This of course gives about half the synch rate of MaxDSL by default-- theoretically much more stable but sooo boring
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Would you say I have a line fault?

Quote
My understanding is that what our routers show as "SNR Margin" is what they measure as the ratio of the signal level above the line noise level


I think you are perfectly correct with that understanding.
In the days before 2mB as the norm we had many people posting their router figures to see if it was worth paying to try and get more than the 512kB that most people were on.
In many of these cases the router just reported with "Margin" instead of SNR. The figures quoted for this "Margin" were almost always similar to those that were giving SNR figures.

Maybe modern routers / modems are quoting it as the margin between what you have and what is needed for a reliable connection but somehow I doubt that.