I am curious if anyone can explain the difference between the SNR number calculated for the CMTS port and the SNR for each individual modem on that port. I have run across a few ports where the number per modem is drastically different than the SNR for the port itself. On the CMTS it would be the difference in running the show cable noise command versus show cable modem phy command.
I have even looked at the average over time for the port and the average per modem for the same time period and they too show a large
difference, more than 20dB. This not a typical situation because the CM and CMTS SNR numbers are generally close, within a dB or two.
Thanks.
The CMTS SNR which you will see on upstream is the average SNR of every cable modem connected to this upstream.
The CM SNR is the particular SNR of the cable modem.
regards,
wittmann
This is what I thought, but there are times when I get a 20dB difference between the two readings. For example, if I were to use the show cable noise command to get the upstream SNR for a particular interface I will show a level of like 16dB. Yet, when I run a show cable modem phy to view the SNR per modem I get an average of about 35dB. And we use some software to show the SNR levels over time and this level difference between the CMTS and the per modem SNR stays constant for weeks. It is not just an issue with a particular snapshot.
I have asked some people at our Network Operations Center and they gave me the same answer, that the CMTS SNR is an average of the individual SNR, but this obviously does not seem to be the case.
I do too see that difference, but with other commands (I usually dont use the show cable noise command). In my case what I do suspect that happens is that one set of operations I am measuring the signals at the CMTS side, while with others at the modems side. And then, some other commands cache the SNMP values for some time, whilst others are the values of the moment.
I am not familiar with you particular commands, but just my 2c.