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Community Manager
Community Manager
Posts: 141

ADSL SNR and Attenuation

I hope this will be helpful

 

Signal to Noise ratio (SNR) and Attenuation are two figures that are often used to indicate the quality of an ADSL line. When logging into your router, you are often able to see these levels, measured in decibels or dB.

 

So what do they mean and what should they be?

 

ADSL is a digital signal transmitted over a copper wire at a certain frequency. Things like electromagnetic interference or line distance can all play a role in the stable and speedy operation of an ADSL line.

 

SNR or Signal to Noise Ratio:
Describes the ratio of usable data-signals on your line. You can associate the “signal”
with the data travelling across your ADSL-line and the “noise” as the unwanted
interference affecting the signal. The higher the number the better for this
measurement. In some instances interleaving can help raise the noise margin to an acceptable level.

 

6dB or below is bad and will experience no synch or intermittent synch problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with little or no synch problems
20dB-28dB is excellent
29dB or above is outstanding

 

Attenuation:
Is the reduction in signal strength on your phone line. In ADSL this may be reported
as “loop loss” and is the natural deterioration of the ADSL signal over distance from
the exchange. 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 oxidisation of joints.
The lower the dB the better for this measurement.

 

20dB and below is outstanding
20dB-30dB is excellent
30dB-40dB is very good
40dB-50dB is good
50dB-60dB is poor and may experience connectivity issues
60dB or above is bad and will experience connectivity issues

 

The standard signal attenuation spread for a given speed is somewhere in the
region of 25-30dB for ADSL1 speeds.


The following guide (distance vs. attenuation vs speed) gives you an guestimate what you can achieve:

 

<1km should be 23-24Mbit
1.0km = 13.81dB = 23Mbit
1.5km = 20.7dB = 21Mbit
2.0km = 27.6dB = 18Mbit
2.5km = 34.5dB = 13Mbit
3.0km = 41.4dB = 8Mbit
3.5km = 48.3dB = 6Mbit
4.0km = 56dB = 4Mbit
4.5km = 62.1dB = 3Mbit
5.0km = 69dB = 2Mbit
> 5.0km (not much hope)

 

You will not be able to fix attenuation (unless you relocate straight next to the exchange).

 

(disclaimer: these figures are approximate and do not guarantee any speed. The line is also still dependent on the physical quality of the copper line and many other external influences.)

New Contributor
Posts: 76

Re: ADSL SNR and Attenuation

Hi AW,

Geat stuff, this really helps as a techie to understand what the significance is of these values, not just smoke & mirrors.

They actually mean something.

 

I endeavor to assist in application of Computer technology where ever I can assist.
Member
Posts: 4

Re: ADSL SNR and Attenuation

Thanks a lot for the info, now I know more or less what the SNR and Attenuation numbers mean! My line has been dropping out periodically (say once or twice every hour) for the past week and I really don't know what could be the cause. If I get Telkom to do a port reset it normally stabilizes for perhaps a day or two before the problem returns. I don't think it's the ISP as I have tried multiple accounts and when the net drops there is no DSL signal at all. It normally takes about 2-3 minutes for it to start working again. Here are my statistics:

 

xdsl.png

 

Can you see anything untoward? The attenuation looks ok but perhaps the Noise Margin is a problem? Any info would be greatly appreciated! As you can see current uptime was 24 minutes since I'd just been throught the process of getting a port reset to try and stabilize the line. Thanks

Community Manager
Community Manager
Posts: 141

Re: ADSL SNR and Attenuation

@timminata the SNR is bad. Have you checked that your POTS filter is correctly connected. Maybe also try swopping it. Also check that there is nothing interfering with the line. Heard of electric gates and sprinkler systems even interfering. Next step then is to report the fault

Member
Posts: 4

Re: ADSL SNR and Attenuation

Thanks for the response. I moved the router closer to the line (it was in another room with a 6-8m cable connecting it and the noise margin has changed a bit, the best reading I have seen is 13 (which I assume is acceptable?). However, even as I came to type this the line dropped again :-( Next step will be to unplug all the phones and see if it changes anything, else log a fault. I am just worried since it's an intermittent fault, what happens if they come to fix it and tell me that there is nothing wrong? Thanks again for the help!

Regular Contributor
Posts: 498

Re: ADSL SNR and Attenuation

@timminata 13dB should usually be fine. As long as all your phones are plugged into filters, then they shouldnt affect your line, as they filter out the different frequency of voice. However it is worth a try to see what ADSL is like with no phones on, especially if there are more extensions as well. Each phone device must have a filter.

Member
Posts: 3

Re: ADSL SNR and Attenuation

[ Edited ]

 

We are seeing intermittent connectivity issues connecting to our first hop and the Internet in general.

The below ping plot demonstrates the issue.

 

 

google-public-dns-a.google.com.pngPing plot over Wi-fi ethernet showing similar packet drops and ping rate fluctuations

 

When we look at the modem status, after resetting statistics.

We see decent SNR 101/81 Margins but worrying attenuation values 325/148.

 

ADSL modem status.pngDSL-2750U Firmware Version: AF_1.72_R01

 

We have already replaced the modem, and disabled the telephone portion of the equation and symptoms remain.

 

Are we experiencing line issues?

Member
Posts: 3

Re: ADSL SNR and Attenuation

[ Edited ]

The user interface of the modem shows a very different picture when compared to the command line outputs.

Looks like the firmware developers ommited including a decimal point in the user interface...

I have reset the statistics and will let the modem collect these overnight for comparison in the morning.

 

 

> adsl info --show

adsl: ADSL driver and PHY status

Status: Showtime

Last Retrain Reason:    0

Last initialization procedure status:   0

Max:    Upstream rate = 1100 Kbps, Downstream rate = 13208 Kbps

Bearer: 0, Upstream rate = 1020 Kbps, Downstream rate = 9215 Kbps

 

Link Power State:       L0

Mode:                   ADSL2+

TPS-TC:                 ATM Mode

Trellis:                USmiley SurprisedN /DSmiley SurprisedN

Line Status:            No Defect

Training Status:        Showtime

                Down            Up

SNR (dB):        10.1            8.2

Attn(dB):        32.5            14.8

Pwr(dBm):        0.0             12.8

 

                        ADSL2 framing

                        Bearer 0

MSGc:           65              10

B:              86              145

M:              1               1

T:              3               1

R:              16              0

S:              0.3009          4.5447

L:              2738            257

D:              96              1

 

                        Counters

                        Bearer 0

SF:             1502            1267

SFErr:          0               0

RS:             319947          20274

RSCorr:         2139            0

RSUnCorr:       0               0

 

                        Bearer 0

HEC:            0               0

OCD:            0               0

LCD:            0               0

Total Cells:    523184          55549

Data Cells:     3926            2722

Drop Cells:     0

Bit Errors:     0               0

 

ES:             0               0

SES:            0               0

UAS:            0               0

AS:             24

 

                        Bearer 0

INP:            2.00            0.00

INPRein:        0.00            0.00

delay:          7               1

PER:            16.02           18.17

OR:             35.44           7.04

 

Bitswap:        0/0             0/0

Member
Posts: 3

Re: ADSL SNR and Attenuation

Herewith the stats as promised:

SNR consistantly below 10db.

Downstream power always at zero?

Downstream attentuation acceptable.

168 uncorrected errors.

620 upstream bit errors.

 

 

> adsl info --stats

adsl: ADSL driver and PHY status

Status: Showtime

Last Retrain Reason:    0

Last initialization procedure status:   0

Max:    Upstream rate = 1100 Kbps, Downstream rate = 13208 Kbps

Bearer: 0, Upstream rate = 1020 Kbps, Downstream rate = 9215 Kbps

 

Link Power State:       L0

Mode:                   ADSL2+

TPS-TC:                 ATM Mode

Trellis:                USmiley SurprisedN /DSmiley SurprisedN

Line Status:            No Defect

Training Status:        Showtime

                Down            Up

SNR (dB):        9.8             8.1

Attn(dB):        32.5            14.8

Pwr(dBm):        0.0             12.8

 

                        ADSL2 framing

                        Bearer 0

MSGc:           65              10

B:              86              145

M:              1               1

T:              3               1

R:              16              0

S:              0.3009          4.5447

L:              2738            257

D:              96              1

 

                        Counters

                        Bearer 0

SF:             2396538         266830

SFErr:          10              24

RS:             510462526               3731004

RSCorr:         3626562         0

RSUnCorr:       168             0

 

                        Bearer 0

HEC:            90              10

OCD:            0               0

LCD:            0               0

Total Cells:    834718448               92286099

Data Cells:     90111931                7034563

Drop Cells:     0

Bit Errors:     0               620

 

ES:             6               17

SES:            0               0

UAS:            0               0

AS:             38393

 

                        Bearer 0

INP:            2.00            0.00

INPRein:        0.00            0.00

delay:          7               1

PER:            16.02           18.17

OR:             35.44           7.04

 

Bitswap:        20/20           0/0

 

Total time = 10 hours 40 min 5 sec

FEC:            3626562         0

CRC:            10              24

ES:             6               17

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

Latest 15 minutes time = 10 min 5 sec

FEC:            56540           0

CRC:            0               0

ES:             0               0

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

Previous 15 minutes time = 15 min 0 sec

FEC:            84179           0

CRC:            0               0

ES:             0               0

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

Latest 1 day time = 10 hours 40 min 5 sec

FEC:            3626562         0

CRC:            10              24

ES:             6               17

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

Previous 1 day time = 0 sec

FEC:            0               0

CRC:            0               0

ES:             0               0

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

Since Link time = 10 hours 40 min 4 sec

FEC:            3626562         0

CRC:            10              24

ES:             6               17

SES:            0               0

UAS:            0               0

LOS:            0               0

LOF:            0               0

LOM:            0               0

>

Established Member
Posts: 7

Re: ADSL SNR and Attenuation

Ok, so now I know a little more about what is going on. 

First let me relate my problem (which is now solved):

I have an ADSL connection via a D-Link DSL-2750U.

Telkom techie Wiseman got my line up and running in double quick time!

My data rates are very acceptable and I cannot report any problems.

BUT . . . . when checking router statistics the attenuation is reported as 340db!

 

adsl speed calc.jpgI know the wiring to my Telkom exchange is NOT 25 Km long.

And the calculator cannot even guess at a speed.

I just knew there is something wrong here.

I tried disconnecting the phone line, rearranging the router wiring, using different types of wire for the connections etc (don't try this - it is a waste of time).

Nothing appeared to improve the attenuation.

 

THEN . . . . . I came accross this thread and saw the remark by JohannO about "command line" stats.

Using TELNET I saw that the actual attenuation is 34.0!  Yes - the GUI omitted the decimal point.

To enable TELNET on Windows 10 try this site:

"https://www.rootusers.com/how-to-enable-the-telnet-client-in-windows-10/"

Thanks to AW for this thread and clearing up what I thought could be a serious problem.

 

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