bsoft
join:2004-03-28
Boulder, CO | reply to iansltx
Re: It's a Chevy, alright ... My understanding (according the the 10th or so Comcast tech I spoke with) was that it was a CMTS configuration issue, not a signal issue. Apparently high upstream channel load would cause a wave of DCCs that would cause CMs to briefly lose connection while they switch to the other channel; this causes TCP to enter either fast recovery or slow start (depending on implementation), cutting bandwidth usage and causing more CMs to be switched to the other channel. Then, TCP starts increasing the window size again, bandwidth usage increases, and the CMTS swaps modems back to the other channel.
The net result is that CMs get flipped around from channel to channel several times an hour (instead of very rarely). |
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iansltx
join:2007-02-19
Golden, CO
kudos:2 | Got it. We only have one main upstream channel here (on my node anyway); the other is 16QAM so everyone gets put on thhe 64QAM one AFAIK. So no disconnects due to loading. |
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bsoft
join:2004-03-28
Boulder, CO | My friend in Golden would bounce between 16QAM and 64QAM all the time. I'm not sure whether we have multiple 64QAM channels here in Boulder, but it's certainly possible. |
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