Packet Loss and Low Upstream SNR

Packet Loss and Low Upstream SNR
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Brocktoon @ 2nd Nov 07:55PM:
Packet Loss and Low Upstream SNR

Hello,

My connection has been pretty solid for the past few months, but due to reoccuring issues in the past, I check my modem signal, packet loss via pings, and speeds on a daily basis.

Just this past week I noticed my modem upstream channel would switch between 8 and 9 frequently, but my connection and signals remained fine. My IP address was also changed automatically two weeks ago ... don't know if the above info has any bearing on my problem, but I figured I'd list it. Also, our area is undergoing the 2nd phase of the digital transition this week. I haven't been having any problems with my cable TV or on demand.

Everything was rock soild on Sunday until around 6:30 PM when all of the sudden my connection began to hang and stutter. I pinged my gateway and was suddenly getting 15-30% packet loss (I usually get 0% loss). When I say gateway, I was using the gateway listed when I checked my comcast IP address, so I guess this may be considered my 1st hop past my modem. My router was not connected. Also, I found that my upstream channel was switched to channel 7 (23.2 MHz). Around 7:30 PM everything went back to normal like a switch was flipped. Then around 8:30 PM the packet loss started again and lasted until around midnight when things were fine again. Checking this morning before work at 6AM, my connection was still great. Returning home today, the packet loss has returned. All this time, my upstream channel has remained Ch. 7. I don't know if the channel assignment can be part of the problem?

During all of these bouts of packet loss, my modem signals have remained consistently good, and there have been no errors in the log. Also, the modem reboots and syncs with no problem. I just have huge amounts of debilitating packet loss that slows everything to a crawl.

I called Comcast last night. The first customer service rep just had me reboot the modem a few times and said everything looked good (even while I was getting the packet loss). I called again today when I got home, and this service rep seemed a bit more knowledgable ... He said that my upstream SNR was below 18 and out of spec
He set up a tech visit for Wed afternoon.

Comcast ran all new coax to and inside my my house a few months ago, so I don't think it's the inside wiring. I see the problem whether running with a router or directly to the modem. I'm seeing the packet loss now, but my current modem signal are psoted below. I'm renting an RCA/Thompson DCM modem from Comcast. I'm on the 16/2 plan, and again everything was rock solid until last night.

FORWARD PATH:
SNR: 37.2
Singal Strength: -7.5
Modulation: 256 QAM

RETURN PATH:
Channel ID: 7
Frequency: 23.2 MHz
Power Level: 47.7
Modulation: 16 QAM

To me, while the signal aren't amazing, they're perfectly acceptabe. Again, the service rep said my UPSTREAM SNR was below 18.

What could cause everything to look good with the modem signals but give a low Upstream SNR. The tech will be out on Wednesday ... should I have him focus on the outside wiring? Is this an issue with the CMTS?

Thanks
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Brocktoon @ 2nd Nov 08:10PM:
Re: Packet Loss and Low Upstream SNR

Hate to post again so quickly, but at pretty much 8 PM on the dot, my packet loss had dissapeared for now and everything is back up to speed. I doubt it's gone for good though. My signal levels never changed, just all of the sudden ... everything's back to normal after packet loss all day ?
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beachintech @ 2nd Nov 08:22PM:
Re: Packet Loss and Low Upstream SNR

If your upstream SNR really is 18, there is a serious noise issue on your node. The tech will need to see this (which he can with his handheld), and then escalate the call up to maintenance. Line techs will then track down the noise and fix it. It's not an instant project and can take some time to find it.
--
Tech at the Beach.
I speak for myself, not my employer.
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Brocktoon @ 2nd Nov 08:36PM:
Re: Packet Loss and Low Upstream SNR

Thanks for the quick response. Since my packet loss dissapeared a few minutes ago, I called up Comcast and asked if they could give me the upstream SNR. They said it's now reading 24-25 (that's just around 90 minutes after it was reading below 18) I don't know how good that is, but it's higher than before and currently no packet loss. There is no change on my other modem signals, just the change in the upstream SNR

Hopefully my connection will be acting up when the tech visits
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gar187er @ 2nd Nov 08:52PM:
Re: Packet Loss and Low Upstream SNR

25 is still bad. The tech you get won't be able to do much other then refer you off for a line call
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