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Mountain View, CA
reply to HeadendJoe

Re: What to do about 11 weeks of node/network problems?

Thanks, HeadendJoe, and JoelC707 See Profile (hi dude ).

As surprising as it might sound, I actually understand most of the terminology you've used, sans two terms: MER and NSG. I know what QAMs are, and I know what BER is (bit error rate; from my experience with DS1/DS3/OC3/OC12 and SONET), but the other two are new to me.

I put in a call to the "general manager" who I'd spoke to in the past (about service technicians). I think I'm going to let things sit until Wednesday.

If I don't get a call back from him by then, I'm going to try an alternate approach -- I do have a contact at Comcast who handles the PR and IP networking side of things, and I have a good relationship with that person. Possibly they can get me in touch with someone who can drive this.

Otherwise if that goes no where, I'll give my LFA a call and approach it from that angle.

I guess on the positive side, there's lots of hard data/evidence that I can provide, and there is a part of me (the engineer part ) that's happy that Comcast was able to confirm existence of the issue. Sometimes tracking down a problem is the hardest part. In this case though it seems to be getting it fixed that's a pain.

Will let folks know what transpires.
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


This is a NSG »harmonicinc.com/product/nsg-9000 ··· -9000-6g

Essentially its an edgeQam that receives optical info and generates the info into RF QAM channels. So how Comcast works is that their CMTS routers are uBR10012 Cisco routers. The Downstream info (signal from the headend device to the node) leaves the router via fiber to the Harmonic NSG. The NSG outputs the info into multiple RF QAMs. Those QAMs eventually reach a transmitter where its converted back to optical, sent to the node, and then converted back to RF. Comcast also uses NSGs to convert VOD optical streams to RF QAMs.

Just a few definitions for you. MER (Modulation Error Rate) is the digital equivalent to SNR, which is the baseband measurement equivalent to Carrier to Noise. MER measures the ratio of error power to average power in an ideal QAM signal. MER measures the difference in quality between the transmitted modulation of a digital signal and the received modulation. Carrier to noise ratio is the measurement of the distance between a modulated RF carrier and the inherent noise floor. You can find a little more detail about these on Wikipedia.

Keep us updated for sure, hopefully it will get fixed. If you end up calling the FCC or your LFA, make sure you ask about Comcast's POP (proof of performance) testing. I believe by law the public has the right to review the outcome of those tests. They do the tests twice a year. May be worth glancing over if you're interested in where they found leaks in the plant during the test.