Suggestions on keeping SNR stable. We are running 64 QAM and every so often are experiencing High fluctuations in our SNR. Seems if we are chasing our tails more times than not. What maintenance work are you doing to keep this number stable as possible?
What channel width are you running, 3.2 or 6.4 ?
That's a good question by mbowe, in the other hand, you can try moving the US freq to a "cleaner" portion of the spectrum.
Couple of other tips :
1) You can enable fallback modulation profiles so that yes try 64QAM where possible, but then if too noisy CMTS can auto drop to 16QAM. Lower QAM rates handle noise better for example 64QAM might barf at 25dB but 16QAM might handle that same level OK.
2) You can enable fallback channel widths so that yes use 6.4MHz where possible, but then if too noisy CMTS can auto drop to 3.2MHz. Gains you an instant 3dB.
3) You can enable spectrum groups rather than hardcoding your US freq. The group can be configured for eg 20 to 42MHz and then if the CMTS detects noise it can auto hop the US to a different freq to try and get away from the noise.
4) You can snmp poll the ussnr, width and qam and graph it in cacti or mrtg. (Or even in worst case just watch the CMTS syslogs and you will see when changes are happening). If you see fluctuations in these settings regularly it is probably a sign you should switch to less aggressive settings for that upstream. Go out in the field and hunt down the noise. Once fixed and SNR is looking nice and clean, flip back to the more aggressive settings.
5) Make sure you have equalization-coefficient enabled on your upstreams (Note that some really old IOS and modems didn't like this. Make sure you are up to date with your firmware on both.
P.S. You need a really clean upstream to run 6.4 width with 64QAM !
We are running 64 QAM on 32 Mhz frequency. Channel Width is 1.6. Should we move the width to 3.2?
Changing the width 3.2 will increase the chance of noise entering the spectrum, first change the frequency as close as 40MHz as you can, try measuring the SNR levels and then changing the channel width.
Hello mbowe,
can u give the sample configuration in port upstream for : Fall Back modulation profile, Fall back channels and spectrum groups? I need this configuration also, but still confused to set up the criteria in cmts.
Thanks in advance!