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Noise Margin, Attenuation Meaning On Smc Router


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Posted
They are perfectly normal.

Attenuation should be below 60, and Noise Margin should be above 12.

In my opinion Attenuation should be below 50! Attenuation over 50db can cause loss of signal.

Posted (edited)

The attenuation depends on the length of the line and the amount of noise on that line.

In simple words: how much power do I have to put in the line to get a signal across it?

The signal-noise ratio depends on the line quality and the adsl speed. The line quality is more or less constant (it is determined by the physical characteristics of the phone line).

The higher the speed, the lower the SNR.

Example of an ADSL line, 8M downstream, 1M upstream, line length 850 meter:

(This is the maximum speed that ADSL supports!)

Downstream Upstream

Modem Status: Showtime (DMTDSL_SHOWTIME)

DSL Mode: ITU G.992.1 (G.DMT)

ITU STD NUM: 0x01 0x01

Vendor ID: 'ALCB' 'BDCM'

Vendor Specific: 0x0000 0x6291

Vendor Country: 0x00 0xB5

Capacity Used: 78% 94%

Noise Margin: 15.0 dB 7.0 dB

Output Power: 12.0 dBm 12.0 dBm

Attenuation: 6.5 dB 3.5 dB

Defect Status: None None

Last Fail Code: None

Selftest Result: 0x00

Subfunction: 0x02

Interrupts: 667 (1 spurious)

Activations: 4

Init FW: embedded

Operartion FW: embedded

SW Version: 3.9.19

FW Version: 0x1A04

Speed (kbps): 8128 1024

The downstream SNR is 15dB, the upstream SNR is 7dB. 7dB seems quite low, but considering the upstream speed of 1Mbps it's still very good.

For 512kbps upstream, the SNR should generally be above 10dB.

CAT sells 2M/800k adsl lines. The actual upstream speed can be higher, depending on the line quality. The dslam trains the line as fast as possible and switches down in speed until a stable connection is established. CAT guarantees that the upstream will be at least 800kbps.

Upstream on my CAT line is 928kbps with a SNR of 6dB. And it works just fine.

edit: text formatting

Edited by Prasert
Posted

Hi,

Thank you for all your replies. I had my phone line replaced, because there was a huge buzzing always on it. These are the new numbers for the new line.

post-77378-1235043928_thumb.jpg

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