Some neat tricks for adsl lines

G

GedMarc

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Hey there

I went ahead and bought Telkom's 4meg line and was only getting 2211 down stream out of it... Going through some vigorous library sundays and a lot of investigation i managed to get my line to 3899 and i thought I'd share how..

Throughout this site everyone says attenuation and SNR, my router works on noise margin so that makes it pretty difficult.
I'm Using a NetGear DGN2000 and I found out that it will keep dropping line speed to get as close to 6db noise margin as possible... You can't get around this but apparently the billion's and other devices do the same thing...

Routers aim for a target noise margin of 6db (for our adsl, 12db for adsl2+) and alter the connection accordingly to reach this target via the snr's....

Attenuation is pretty important too yes, but according to this diagram (Accurate) :

internode-adsl2-dist07.jpg


Attenuation of 51db is 4.6mb, with 57 at 3.8mb on the 8meg ADSL lines... My attenuation is perfectly fine for a 4mb connection, just not capable of more. But that's fine I'm paying for 4megs.

Using our copper wires, you take your attenuation, and divide it by 13.81 (because standard gauge copper (0.4mm) has a loss of approximately 13.81db/km).

So I am 3.4km's away from the nearest exchange. Confirmed with Telkom.

My stats were pretty straight forward :

down up with filter
speed 2259 507
atten. 47 33.5
n/m 6.3 6.6

So the router is doing the right job and trying to get to a noise margin as close to 6 as possible but the speed is half of what it should be according to the attenuation.
This led me to testing internals...
Doing an isolation test i got the following :

down up

speed 2315 507
atten. 47 33.5
n/m 6.1 9.4

My phone socket is somewhat close to my stove and toaster and kettle, so turning off the wall socket for my kitchen and rebooting my modem i then got the following :

down up

speed 3345 507
atten. 47 33.5
n/m 6.6 11

Instantly I realised ok, being in a summer-con complex obviously they went cheap on the wiring and it's creating a lot of noise on the line...

Upgraded and requested telkom to move my line out of my kitchen, putting the router far away from any electronical devices, and making sure that my 50" telephone cable does not go past any speakers (NB), fridges, or electronic devices I now sit with :

down up

speed 3849 507
atten. 47 33.5
n/m 5.9 12.1

I hope this helps :)
 
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Well done on determining the fault on your own!

The following part of your post does not make sense or isn't stated clearly:
GedMarc said:
Attenuation of 51db is 4.6mb, with 57 at 3.8mb on the 8meg ADSL lines... My attenuation is perfectly fine for a 4mb connection, just not capable of more. But that's fine I'm paying for 4megs.
Click to expand...
Perhaps you should've said it like follow:
With G.DMT modulation (referred to as ADSL (up to 8Mbps) on the chart, your maximum downstream speed are:
4.6Mbps when the downstream line attenuation is 51dB
3.8Mbps when the downstream line attenuation is 57dB

GedMarc said:
Using our copper wires, you take your attenuation, and divide it by 13.81 (because standard gauge copper (0.4mm) has a loss of approximately 13.81db/km).
Click to expand...
I usually just divide by 14 or 14.5dB as it gives a close enough estimation.

The attenuation readings on the ADSL modems would differ slightly for G.DMT and ADSL2+ modulation, so using 13.81dB/km is just plain silly.
Secondly, it should be stated clearly that the "Line Attenuation (dB at 300Khz)" on the chart, as well as the 13.81dB/km ratio is ONLY applicable to the downstream line attenuation !

I don't like the chart, because it is for perfect conditions and not real world situations.

Lastly, the ADSL modem chipsets also plays a big role in terms of stability and maximum line speeds.
 
GedMarc said:
noise margin as close to 6 as possible
Click to expand...
Wait a second, isn't an SNR value of 6 the "die-out" position, from what I understand the higher the SNR the better, the lower the attenuation the better, please correct me if I'm missing something :erm:
 
Segg said:
Wait a second, isn't an SNR value of 6 the "die-out" position, from what I understand the higher the SNR the better, the lower the attenuation the better, please correct me if I'm missing something :erm:
Click to expand...
Yup.

SNR or Noise margin is an indication of how well it can tolerate faults - hence higher value is better.
The line attenuation is the signal loss due to the length of the ADSL line - hence lower value is better.

You need a minimum SNR of 6dB to be able to have a working ADSL connection.

SNR and noise margin is one and the same thing, although some devices might show the Noise margin as SNR - 6dB, which would mean that they can show a Noise margin with a value lower than 6dB and still have a fully working ADSL connection going.
 
I also have the DGN2000, it's an excellent router.

If your so inclined you can download the DGTeam firmware for it. It allows you to play with some more advanced settings on the router than the standard firmware.
 
I think what he means by the router trying to attain an SNR of 6 is that, provided you have the capability (I.e a 4meg/10meg line with telkom) the router will keep shifting up a speed until it hits 6SNR. you might be able to have a 4 meg with 10SNR, but the router will choose a 6 meg with 6 SNR if it were to be given the opportunity.

*Note - Values stated above are not accurate and are for demonstration purposes only.
 
But our sync speeds are predefined by Telkom.

In the UK and US (the places I've heard they are doing this) they try to get the highest sync possible by the above method. You could even use tools like DMT to change the SNR, and thus sync speed. That's why it'll take a day or two to get the highest possible speed profile.

Correct me if I'm wrong though.
 
Very good post and well done on your research! Best post of the day!
 
M3mPh1z said:
SNR = Sound to Noise Ratio. It's the same thing.
Click to expand...
Nope. It is Signal to Noise Ratio.

In South Africa your ADSL modem would try to use the fastest possible speed, until it either hits the minimum of 6dB SNR margin OR the Telkom ADSL profile limit (eg. 10Mbps or 1Mbps or 384kbps). Usually it can alter the downstream and upstream speeds separately.
 
Tl; Dr
Make sure your interwebz cables do not go near other electrical things in you house
 
Sorry about the thread resurrection.

If I understand this correctly according to the above I currently sync at 6MB but that is my router limiting me to that speed to reach the 6dB snr. Telkom will have me on a 10MB profile?

Is that correct?
 
Hi,

Can anyone tell me if ReADSL2 is possible in south africa if i use a modem that is capable? i have line attenuation of 62dB because im about 5km from the exchange and looking at the graph in the OP it seems i could improve my line sync, which is currently stable only at 3mbps by about 0.5mbps?
 
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SNR should be 12db or higher for acceptable ADSL functioning. You will lose synch with anything below 6db. 6db is terrible.
The router and port are auto adapting your speed to maintain synch. That's why you aren't synching at 406kbps. Possible line fault. Get Telkom to check it out
 
bokka1 said:
Sorry about the thread resurrection.

If I understand this correctly according to the above I currently sync at 6MB but that is my router limiting me to that speed to reach the 6dB snr. Telkom will have me on a 10MB profile?

Is that correct?
Click to expand...

Give Telkom a ring a check what profile you set on. Although you have 10meg, they can adjust the speeds to 8meg, 7meg ,6 meg and 5meg. Maybe it was downgraded to stabilize link due to distance etc. You will have problems with a SNR of 6. Any increase in speed will drop the SNR and anything below 6db = no synch.
 
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Sachin1804 said:
Give Telkom a ring a check what profile you set on. Although you have 10meg, they can adjust the speeds to 8meg, 7meg ,6 meg and 5meg. Maybe it was downgraded to stabilize link due to distance etc. You will have problems with a SNR of 6. Any increase in speed will drop the SNR and anything below 6db = no synch.
Click to expand...

Seriously? Did you confirm this with someone at Telkom? The call-centre dude I chatted to said they could only adjust sync at 8, 4, 2 & 1. I'm hoping they were wrong, and you are right, because 6mb would be my sweetspot!!
 
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