7800DXL - sudden change of SNR Margin

[peterb99]

Hi,

I've been running my 7800DXL for several weeks now, on the latest firmware and with no SNR tweaking. I am currently on Demon ipStream but apparently they are 'upgrading' me to ADSL2+ in October.

In the last couple of days I've noticed my SNR Margin (downstream) has fallen to around 2.8 (see stats quoted below) from consistently >8 previously. The attainable rate has increased from ~2800 previously to 3544 and the actual rate quoted is currently 3392 whereas previously it was around 2400.

Standard web page speed tests show there has been no change to actual speed or even a small reduction.

Please can anyone explain what may be happening? I've not changed any router settings so does this mean there is activity at the exchange? Also, 2.8 SNR Margin - surely that's a bit low for a consistent connection? As you can guess,I live some way from the exchange.

I haven't previously tried SNR tweaking as I'd valued a reliable connection but it seems I'm seeing the result of it currently anyway!

DSL stats as at today:

-----------------------------------------
Mode ADSL_G.dmt
Traffic Type ATM
Status Up
Link Power State L0

Downstream Upstream
Line Coding (Trellis) Off Off
SNR Margin (dB) 2.8 20
Attenuation (dB) 49.5 28
Output Power (dBm) 18.6 11.9
Attainable Rate (Kbps) 3544 1028

Rate (Kbps) 3392 448

K (number of bytes in DMT frame) 107 15
R (number of check bytes in RS code word) 16 16
S (RS code word size in DMT frame) 2 2
D (interleaver depth) 8 2
Delay (msec) 4 4
INP (DMT symbol) 0.28 0.06

Super Frames 16810455 16810455
Super Frame Errors 3087 343
RS Words 181639245 45409728
RS Correctable Errors 24802335 36
RS Uncorrectable Errors 6014 0

HEC Errors 9106 341
OCD Errors 17 0
LCD Errors 17 0
Total Cells 1815331048 0
Data Cells 73664645 0
Bit Errors 0 0

Total ES 747 0
Total SES 29 0
Total UAS 32 32
--------------------------------

Thanks!

Pete

[billion_fan]

Hi,

I've been running my 7800DXL for several weeks now, on the latest firmware and with no SNR tweaking. I am currently on Demon ipStream but apparently they are 'upgrading' me to ADSL2+ in October.

In the last couple of days I've noticed my SNR Margin (downstream) has fallen to around 2.8 (see stats quoted below) from consistently >8 previously. The attainable rate has increased from ~2800 previously to 3544 and the actual rate quoted is currently 3392 whereas previously it was around 2400.

Standard web page speed tests show there has been no change to actual speed or even a small reduction.

Please can anyone explain what may be happening? I've not changed any router settings so does this mean there is activity at the exchange? Also, 2.8 SNR Margin - surely that's a bit low for a consistent connection? As you can guess,I live some way from the exchange.

I haven't previously tried SNR tweaking as I'd valued a reliable connection but it seems I'm seeing the result of it currently anyway!

DSL stats as at today:

-----------------------------------------
Mode ADSL_G.dmt
Traffic Type ATM
Status Up
Link Power State L0

Downstream Upstream
Line Coding (Trellis) Off Off
SNR Margin (dB) 2.8 20
Attenuation (dB) 49.5 28
Output Power (dBm) 18.6 11.9
Attainable Rate (Kbps) 3544 1028

Rate (Kbps) 3392 448

K (number of bytes in DMT frame) 107 15
R (number of check bytes in RS code word) 16 16
S (RS code word size in DMT frame) 2 2
D (interleaver depth) 8 2
Delay (msec) 4 4
INP (DMT symbol) 0.28 0.06

Super Frames 16810455 16810455
Super Frame Errors 3087 343
RS Words 181639245 45409728
RS Correctable Errors 24802335 36
RS Uncorrectable Errors 6014 0

HEC Errors 9106 341
OCD Errors 17 0
LCD Errors 17 0
Total Cells 1815331048 0
Data Cells 73664645 0
Bit Errors 0 0

Total ES 747 0
Total SES 29 0
Total UAS 32 32
--------------------------------

Thanks!

Pete

All this means is the exchange has adjusted to your new equipment and highered your downstream speeds (I assume as it detects a more stable connection it has tried to higher your speeds to see if you still have stability, but it should not drop as low as 2.8db, they might be upgrading the exchange as you stated), when the downstream sync speeds increase, normally the SNR will drop also.

I don't think there is anything to worry about (as you have increased speeds) I would montior the connection for the time being.

With the broadcom chipset, the router should be able to handle low SNR reading.

[peterb99]

Hi billion_fan,

Many thanks for your reply. The only thing I'd say is that I've had my 7800DXL for at least a couple of months and it's only the last couple of days that I've seen this low SNR Margin (2.7 as I write this). Demon told me the exchange was coming off ipStream in October.

The only thing I've started doing recently is using the new reboot facility in the router to reboot once a week overnight.

Although the stats indicate I should be getting a faster speed the flash based speed tests suggest not (if anything slightly the reverse!) and subjectively it feels much the same as previously.

I can live with it either way, I was just interested. If it stays at 2.7 should I be using your tweak table to increase it back to around 6? (Sorry, probably a dumb question but the tweaking thing seems somewhat of a black art plus I'm unsure if a tweak at the router end causes a compensating adjustment at the BT end.)

Thanks again!

Pete

[billion_fan]

Hi billion_fan,

Many thanks for your reply. The only thing I'd say is that I've had my 7800DXL for at least a couple of months and it's only the last couple of days that I've seen this low SNR Margin (2.7 as I write this). Demon told me the exchange was coming off ipStream in October.

The only thing I've started doing recently is using the new reboot facility in the router to reboot once a week overnight.

Although the stats indicate I should be getting a faster speed the flash based speed tests suggest not (if anything slightly the reverse!) and subjectively it feels much the same as previously.

I can live with it either way, I was just interested. If it stays at 2.7 should I be using your tweak table to increase it back to around 6? (Sorry, probably a dumb question but the tweaking thing seems somewhat of a black art plus I'm unsure if a tweak at the router end causes a compensating adjustment at the BT end.)

Thanks again!

Pete

Hi Pete

Its upto you if you wish to higher the SNR back to 6db, I would personally leave it as is as long as you don't notice any DSL drop outs etc.

[peterb99]

Hi Pete

Its upto you if you wish to higher the SNR back to 6db, I would personally leave it as is as long as you don't notice any DSL drop outs etc.

Yes thanks, good advice. My internet seems as stable as it was before I noticed the SNR change so I'll just leave it alone.

I do just love this router though!

Pete