Attenuation - different values different routers?

I have several Netgear routers with ad7 chipsets which report my downstream attenuation as 56db - when I fire up my DG834PN, which is my only Broadcom chipset router, it reports 60.0db (back to back test - same leads etc - same result when reverting to the PN)

Is this just the normal range of accuracy I should expect from this class of equipment, or is it likely that I have some problem with the PN?

(I closed this question opened earlier in the wrong forum apologies )

From the G.992.1 spec:

" Attenuation (ATN): The attenuation is the difference in dB between the power received at
the near-end and that transmitted from the far-end. Received signal power in dBm is the sum
of all data-carrying (i.e. bi > 0) DMT subcarrier powers averaged over a 1 second period.
Transmitted signal power is �3.65 �2n + 10 log ( gi ) dBm, summed over the data-carrying
subcarriers. The attenuation ranges from 0 to 63.5 dB with 0.5 dB steps."

In other words the attenuation reported will depend upon the tones a particular modem has chosen to use. Different modems use different algorithms to decide which tones to use.

Edited by deleted (Tue 19-Aug-08 09:59:02)

Is that variation of 4db nomal or unusual? - The AD7 routers did not vary much between each other. I am still trying to get a veiw as to whether
I have a sick DG834PN or am looking at normal variations between routers or perhaps chipset types.

What sort of variation have other people seen between routers?

Some stats from the 'PN at the moment:-



Noise Margin: 15.4 dB
Connection Rate: 2080 Kbps
Line Attenuation: 60.0 dB
Power: 17.4 dBm

SF: 1261950
SF Errors: 17
Reed Solomon: 42906312
RS Corrected: 2158
RS Un-Corrected: 101
HEC: 15
Errored Seconds: 9
Severe ES: 0
Interleave Depth: 16
Noise Margin: 15.4 dB
Connection Rate: 2080 Kbps
Line Attenuation: 60.0 dB
Power: 17.4 dBm

SF: 1261950
SF Errors: 17
Reed Solomon: 42906312
RS Corrected: 2158
RS Un-Corrected: 101
HEC: 15
Errored Seconds: 9
Severe ES: 0
Interleave Depth: 16
Total Up Time:
6 hours 1 min 12 sec

CRC: 17
LOS: 0
LOF: 0
ES : 9


Bytes Transferred (ppp0):
Tx: 847112 (827.2 KiB)
Rx: 4182939 (3.9 MiB)

I don't think a 4-6dB difference between routers is remarkable, but that is only a feeling and I have no evidence to offer.

To get a proper answer would require a laboratory with an ADSL line which could be exercised in a controlled way.

OK - thanks for that - I have another Broadcom router coming so I will do another comparison when I have that and report back what I find.

In the meantime I will try and leave my line in peace for a while to try to let it speed up a bit - hopefully all my disconnects while updating firmware and swopping routers has not got me locked down to 15db margin.

In reply to:

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What sort of variation have other people seen between routers?

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A Voyager 210 recorded a downstream attenuation of 57dB for my line,
whereas the SpeedTouch 585 v6 I am using gives a figure of 54 dB.

Have a look at the certificate of calibration supplied with each your routers.

These certificates are conspicuous by their absence!

As John2007 has said

In reply to:

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To get a proper answer would require a laboratory with an ADSL line which could be exercised in a controlled way.

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Each router is correct.
Each router is equally incorrect.

Use the figures obtained for guidance/comparison purposes only.

N.B. If you ever have an OpenReach (or other supplier) engineer visit your premises for ADSL problems, be sure to ask for a look at the equipment calibration certificate if he/she declares that no problem exists. It could save you ~�150.00.

Hi

In reply to:

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I have several Netgear routers with ad7 chipsets which report my downstream attenuation as 56db - when I fire up my DG834PN, which is my only Broadcom chipset router, it reports 60.0db (back to back test - same leads etc - same result when reverting to the PN)

Is this just the normal range of accuracy I should expect from this class of equipment, or is it likely that I have some problem with the PN?

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As others have said the attenuation typically shown by routers is an average. Having a higher attenuation may mean you are receiving higher frequency tones you didn't get before, this is good, and just skews the average higher as they are being received with much higher attenuation.

The attenuation quoted by BT after tests is usually at 300KHz and not an average, and this will be the same on any router if you can get this value (inside the tolerance of consumer boxes). You can sometimes get this figure from DMT with compatible modems.

Regards

Phil

Interestingly I noticed after downloading DMTv8.05 (thank for the tip) that on the bottom graphic, before you try to graph the SNR, there is a channel charecteristics graphic which amonst other things quotes the attenuation at 300khz - 57db for my DG834PN whereas the average shown on the router stats is 60.0db

I have now received and reconfigured a Sky DG834GT and fired it up - that's the broadcom chipset again and this time the average is 59db and at 300khz it's 55db

I will run this one for a day then try the AR7 ones again - don't want to resync more than once or twice a day as I already seem to be stuck on 15db margin plus interleaving even though I have not lost sync un-intentionally for days

Edited by dfoss (Wed 20-Aug-08 17:59:21)

"on the bottom graphic, before you try to graph the SNR, there is a channel charecteristics graphic which amonst other things quotes the attenuation at 300khz"

or am I confusing SNR at 300khz with attenuation?