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Category: Tools

Cisco 877 SNR Adjustment for Stability

I managed to find out a secret setting within the 877 to fine tune the SNR margin if you are having stability issues maintaining adsl line sync.

Go into global configuration mode and type the following:
service internal
int atm 0
dsl noise-margin (a value between -3 and 3)

The service internal command exposes the dsl noise-margin command (and other hidden/non standard commands). The dsl noise-margin forces the router to training at a higher noise margin (sacrificing speed for stability). Setting this to 3 for example should see you get a higher noise margin, slower speed (and depending on firmware) a higher attenuation.
Start at 3 and work your way down to 0 in 0.5 steps until you get a stable connection. A value of 0 is the same as not having this command at all (eg: normal settings).
If you add a dsl noise-margin command, after a reload you’ll see “WARNING: Unsupported Command. May cause violation to ADSL standards.” on bootup, ignore it, it’s just the addition of the noise-margin command.
Use the dsl noise-margin command to fine tune your connection to get that extra stability if required.



Cisco 877 & Billion 7402R2M SNMP OIDs

Did you ever want to use the power of SNMP to create graphs with Cacti, MRTG etc? I’ll make you’re life a bit easier by posting the OIDs used by Cisco 877 & Billion 7402R2M modems to get line speed, SNR, attenuation etc

Cisco 877 SNMP OIDS (These work with the latest IOS imageĀ  (C870-ADVSECURITYK9-M), Version 12.4(22)T

. = line speed out
. = line speed in
. = output power out
. = output power in
. = attenuation down
. = attenuation up
. = SNR down
. = SNR up

Billion 7402R2M SNMP OIDS (These work with the latest firmware 5.60c)

. = downstream attenuation
. = upstream attenuation
. = downstream SNR
. = upstream SNR
. = line speed downstream
. = line speed upstream