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Building a remote spectrum analyzer (Pre-eq)

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skyler.blumer
Building a remote spectrum analyzer (Pre-eq)

I'm working on writing my own remote real-time spectrum-analyzer using SNMP. Today the company I work for uses a third party tool powered by 'Nimble This'. We have a combination of Cisco 10ks and 7200s, even one with an NPE-G1, so I don't believe 'Nimble This' uses the docsisIf3Mib.

I'm trying to poll average Pre-Eq data on a per upstream basis. Does anyone have experience polling this information directly from the CMTS? I had varied results with a few different OIDs.

docsIfSigQEqualizationData (1.3.6.1.2.1.10.127.1.1.4.1.7) returns hex data on some CMTS', some CMTS' I get an empty string for all upstreams, and on some CMTS' only a few upstreams return the hex data.

docsIfUpChannelPreEqEnable (1.3.6.1.2.1.10.127.1.1.2.1.19) Always returns and integer of 1. SNMP setting it to 2 makes no difference the docsIfSigQEqualizationData output.

docsIf3CmtsSpectrumAnalysisMeasEntry(1.3.6.1.4.1.4491.2.1.20.1.26.1) appears to not be implemented in IOS or at least the version we're running.

docsIf3CmtsCmUsStatusEqData(1.3.6.1.4.1.4491.2.1.20.1.4.1.6) works on all of our D3 CMTS' (returns data on a per modem basis). This seems like a last resort, because I need to present this as real-time, and I don't think this is what 'Nimble-This' does, because our current tool works on a D2 CMTS'.

Ideally I'd like to just use docsIfSigQEqualizationData. Does anyone know if this requires a configuration setting or an SNMPset that I'm missing to work on all upstreams?

Secondly, is anyone familiar with how the 'Nimble-This' implementation is doing this? Are they just polling modems directly?

mbowe
I am not an expert, but I

I am not an expert, but I know a little bit about the topic of pre-eq

The data needs to be polled from the modems and the CMTS

The data on the modems shows the equalizer coefficients being applied there to pre-distort the signal.

The data on the CMTS shows the equalizer coefficients of the received signal (ideally the signal will be flat).

DOCSIS 2.0 (per modem)
CM docsIfCmStatusTable
CMTS docsIfCmtsCmStatusTable

DOCSIS 3.0 (per interface per modem)
CM docsIf3CmStatusUsTable
CMTS docsIf3CmtsCmUsStatusTable

If you have a lot of modems, then the polling will likely need to be done on a tiered basis :
* Green level modems have good signals and are polled infrequently (maybe daily or hourly)
* Yellow level modems are ones having some signal troubles, and are polled more often
* Red level modems are ones with bad stats, and are polled often

You should read this doc for more info
https://apps.cablelabs.com/specification/proactive-network-maintenance-u...

Dont know a lot about the live spectrum analyser though. I believe it is just MIBs on the modem and CMTS. You set the start and stop frequency, the number of steps (resolution), the run time, and then set another MIB to start. You can then poll the waveforms via another MIB. If I was you, I would fire up wireshark on the device running the spectrum analyser app, and that will show you the snmp MIBs / values being used. Or use wireshark against another app like this one http://www.msarmento.com.br/cmts_monitor.php