Understanding SNR and Attenuation Rates

Signal-to-noise ratio
Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering measurement defined as the ratio of a signal power to the noise power corrupting the signal.
In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is. The concept can also be understood as normalizing the noise level to 1 (0 dB) and measuring how far the signal 'stands out'. In some instances interleaving can help raise the noise margin to an acceptable level.
In general, higher signal to noise is better; the signal is 'cleaner'.

Attenuation Rate
Attenuation is the gradual loss in intensity of any kind of flux through a medium(i.e. the reduction in signal strength due to length of your phone line). For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead.In ADSL the signal is attenuated by length of copper lines. Attenuation is normally directly linked to the length of your line. Copper is traditionally used in the local loop and the higher gauge of copper will give the best signal, however some lines may have some aluminium or aluminium joints on the line which will increase resistance... as will oxidization of joints. Attenuation is mesured in db or noise. The more noise the weaker the data signal
In general, lower Attenuation is better; the signal is 'stronger'.
 
Mine? (Mode is ADSL2+)

Downstream /Upstream
SNR Margin (dB): 11.6 / 12.0
Attenuation (dB): 43.0 / 24.0
Output Power (dBm): 2.6 / 14.0
Attainable Rate (Kbps): 7880 / 1028
Rate (Kbps): 4095 / 511
 
Last edited:
IRG:
You can attempt to upgrade to like 6Mbps, but it might become unstable at anything above 4-5Mbps.
 
IRG said:
Yeah thought as much .... I'll leave it at 4mb :(
Click to expand...
Your modem said that the maximum possible speed at which it could connect is ~8Mbps down/1Mbps up, so you could really give 5-6Mbps a try and it might still be stable.
If you have a 4Mbps uncapped account, then you would get a slight gain by upgrading your line to 5Mbps, because then you could actually get an actual data throughput of 4Mbps instead of just 3.4Mbps.
 
Mineer said:
I would throw a little caution, such low attenuation could be signs of problems with your line. But having said that if you not experiencing problems then there is no need to worry.
Click to expand...

I don't have any problems with my line or internet connection. I just checked and the Telkom box is probably 20m from my house, this is probably why it's so good.

I have phoned Telkom and they say that the exchange does not support 10mb :(
 
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Zona exterior del Balneario.

La zona exterior le permitirá disfrutar bajo el sol de las instalaciones al aire libre. Piscina con jets, chorros cervicales, solarium natural , etc...
 
I'm "on the borderline" for ADSL according to the Telscum techie that came and installed an extra jack the other day.

My attenuation is 26dB up and 54dB down, my line syncs at between 4000kbps and 6700kbps down on average and usually sits on 635 up but it was on 1007 up a few weeks ago. Tends to jump around a lot but the connection itself is quite stable.
 
blunt:
It sounds to me like poor connections at the DSLAM. If this is the case, the technician can easily clean up the ends of the cable and reconnect your ADSL, which should lower your line attenuation by a reasonable margin. Doing this would could allow you to connect at like 6Mbps again.

Unfortunately I can't say whether this is the problem, unless you knew that your line attenuation values was much lower previously.

You're lucky to be able to sync at roughly 4Mbps with such high line attenuation values.
Could you perhaps also tell us what ADSL modem you've got. I'm quite curious to know, because it sounds pretty good so far!
 
Pada said:
blunt:
It sounds to me like poor connections at the DSLAM. If this is the case, the technician can easily clean up the ends of the cable and reconnect your ADSL, which should lower your line attenuation by a reasonable margin. Doing this would could allow you to connect at like 6Mbps again.

Unfortunately I can't say whether this is the problem, unless you knew that your line attenuation values was much lower previously.

You're lucky to be able to sync at roughly 4Mbps with such high line attenuation values.
Could you perhaps also tell us what ADSL modem you've got. I'm quite curious to know, because it sounds pretty good so far!
Click to expand...

Hi Pada,

The Telkom techie previously phoned through to the technicians and told them to cap me to 4Mbps and it was pretty solid on 507/4095kbps but as I knew the line could sync higher I phoned and asked them to open me up to 10mb again.

I'm using a Sitecom WL-322 router, it is not bad but lacks some features that I would like, particularly around advanced settings for the DHCP server (eg: IP reservation based on MAC address) - and the fact that changing ADSL accounts you need to use their "wizard" each time. But other than that it's been good to me and at least it's Wireless N (which at the time I bought it was difficult to come by in combination with an ADSL modem all in one).

What I did last night was, rather than setting my router to use "Automatic" operation mode, I set it to be G.992.5 (ADSL2+) and my attenuation has dropped on the downstream to 49dB, upstream is still 26dB but that's pretty decent anyway. I know that my attenuation has _always_ been on 54dB and sometimes on 56dB but never below, so I'm quite happy about that. Sync hasn't improved that much but it's acceptable as I'm on 4MB uncapped.

Up Stream - 635 (Kbps.)
Down Stream - 4356 (Kbps.)
 
blunt:
If you want to get your line stable, I'd suggest that you contact Telkom and ask them to set your line speed to 4Mbps.
This way you have a slightly higher error tolerance, which would mean that your ADSL would disconnect less often.
 
Hi

I just moved into new place managed to get Telkom to finally install my line.I asked for a 4 meg line, but telkom says that I can only get 384kb download speed.

Here are the figures from my netgear modem.
Downstream / upstream

Line attenuation 61.0 / 31.5 dB
Noise margin. 11.9 / 12.0 dB

What recourse do I have ?

Thanks
Rax
 
rax_m:
Your situation looks pretty weak. You could try a 1Mbps connection, but I suppose even that would be unstable.

According to your line attenuation, you're simply too far away from the DSLAM.
 
Pada said:
rax_m:
Your situation looks pretty weak. You could try a 1Mbps connection, but I suppose even that would be unstable.

According to your line attenuation, you're simply too far away from the DSLAM.
Click to expand...

Thanks for the reply Pada.

That sucks! :cry:
Guess I'm going to have to go for 3G.
 
Hi all.

We have about 4 phone jacks in the house.
The one I connect the ADSL to gives me an attenuation of 61db and a SNR of around 11.
If I connect the ADSL to another jack, I get similar readings.
Is this definitive proof that high attenuation is simply due to distance from exchange, or is there a "core / master" jack in the house that all the lines go to, and that one might be 'faulty'?

Do telkom charge to come out and re-do the wiring?
 
XperiAnce:
The attenuation reading will influence the SNR. The downstream attenuation changes by about 14dB/km.

So extending the telephone line in your home would barely make any difference. If you extend it by 50m, then it could change like 0.7dB.

First see what the attenuation values are when you don't connect any telephones or filters - just the ADSL.
If it is still that high, then you're most likely too far from the DSLAM/Exchange to get a fast ADSL connection (meaning you'd be stuck on like 384kbps - 512kbps).

You can ask Telkom to tell you how far you are from the DSLAM, which you can then take to estimate what your downstream line attenuation would be like by multiplying the km's by 14dB/km ;)
 
Thanks for the update Pada.

I'm also looking at my work line and the stats are as follows (4MB):

Parameters
Downstream Upstream
SNR Margin 23.5 dB 1.4 dB
Line Attenuation 15.0 dB 7.5 dB

Now the downstream values are fantastic, but the upstream SNR Margin of 1.4dB, is that something to worry about?

Below is a traceroute, which is ugly as you can tell:
C:\Users\Michael>tracert www.mweb.co.za

Tracing route to www.mweb.co.za [196.2.63.110]
over a maximum of 30 hops:

1 2 ms 1 ms 1 ms 192.168.1.200
2 2 ms 2 ms 2 ms 10.0.0.254
3 628 ms 271 ms 235 ms 41-133-86-1.dsl.mweb.co.za [41.133.86.1]
4 375 ms 130 ms 142 ms 197-80-4-94.jhb.mweb.co.za [197.80.4.94]
5 214 ms 212 ms 225 ms vl-92.vic-hscore-2.mweb.co.za [196.22.189.3]
6 91 ms 85 ms 96 ms tengig0-7-0-2.12.vic-p-2.mweb.co.za [196.22.169.242]
7 86 ms 70 ms 58 ms TenGigE0-0-0-0.cpt-p-1.mweb.co.za [197.84.4.34]
8 156 ms 166 ms 196 ms vlan11.cpt-hscore-1.mweb.co.za [196.28.178.99]
9 292 ms 284 ms 362 ms 196.28.178.66
10 314 ms 313 ms 92 ms cte-core-sw2.vwol.net [196.41.144.35]
11 165 ms 195 ms 173 ms www.mweb.co.za [196.2.63.110]

Trace complete.
 
XperiAnce:
Could you get hold of your line speed too?

I see that your latencies are very erratic, which could either be due to your work download/uploading lots of data while you're doing the trace route, or it could be due to an unstable connection (low SNR).
 
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