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swalker

join:2006-03-24
reply to koitsu

Re: [Connectivity] New SB6120/6121 Firmware Released

said by koitsu:

I'd like to know where you got the power level "guideline" numbers for upstream channel bonding from. This is the first I have ever seen this mentioned (specifically that multiple bonded upstream channels have more strict power levels). Even the FAQ doesn't jibe with those numbers. So where did you get them? To my knowledge based on service techs I've spoken with in the past, anything above 52dB is considered "volatile", meaning "not acceptable" and Comcast will do something about it, regardless of channel bonding in use or not (this is also supported by the FAQ). I've also been told that 54 dB is permitted on rare occasion (when the environment/cabling/topology is analysed and determined to be as good as it'll get).

»[Connectivity] Bonded upstream and modem sync/T4 issues


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

Interesting! I reviewed my modem logs for the past 30 days, and I can confirm that I've ONLY seen a power level higher than 52dB on upstream channels using QAM16 modulation. Those using QAM64 appear to top out at about 51dB for me. So thanks for pointing me to that information -- I appreciate being corrected and learning something! (Looks like the DSLR/BBR FAQ should be updated to reflect this too, at least as far as when bonding on DS3.0 is in use).

The bug/issue andyross See Profile was experiencing in that thread looks like it should be fixed in 1.0.6.8 (2nd bulletpoint of section 8.1.2 of the release notes posted by DrDrew See Profile); meaning the modem shouldn't continually reboot in that situation any longer.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.

bman212121

join:2005-06-09

That's interesting koitsu. That would definitely explain why it T4's faster than I thought it should. (Was thinking 52db max because the QAM16 would show that)

The one thing I'm not sure if it was addressed or not was when I had even better signal levels than I do now my modem would "runaway" and T4. I would start at 44dBmV on all of the channels and it would creep up to 48dBmV. From there it would either go up to 51dBmV and time out or come back down to normal levels. 7dBmV is a lot of swing and might have indicated another issue they were having.



koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

Agreed -- 7dB is a very big delta. I imagine some of the techs here on the forum might have some ideas as to how things could start at 44 then eventually "settle" at 51. I personally haven't ever seen that, but I totally believe you, and would love to know how that kind of thing manifests itself (or if it's normal at that). Always interested to learn more about cable tech!
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL

My rough theory is that the modem may not be cleanly transmitting and some noise could be leaking between channels, causing issues at the CMTS.