We have couple Cisco 877 ADSL routers in some remote offices. To verify the ADSL line works properly, we add the routers into our Nagios monitor list.

SNR (Signal to Noise Ratio) and Attenucation are two key measurements that tell you the performance of the ADSL line:

  • SNR reflects the signal strength to the level of noise on the line. The higher the SNR value is, the better performance you get. As there is less background noise. It is measured in dB.

      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 no synch problems
      20dB-28dB is excellent
      29dB or above is outstanding

  • Attenuation is the term used to describe the reduction of the ADSL signal strength that occurs on the copper pair over distance. So the lower the attenuation value is, the better performance you got. It is also measured in dB.

      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

To add the ADSL router into the monitor list, you can follow the Nagios XI monitor wizard and choose the SNMP monitor. Then make Nagios to monitor the following OID.

SNR in/out: . / .
Attenuation in/out: . / .
Outputpwr in/out: . / .
Linespeed in/out: . / .

The following are the performance graphs in my Nagios XI. The unit is 0.1 dB.