Visitor
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3 Messages
DOCSIS3.0 is slow but consistent while DOCSIS3.1 is faster but fails often
I have Xfinity high speed service in the SF Bay Area and have been frustrated with the following issue. My OLD Netgear CM600 (DOCSIS3.0) works well and is stable, but limits my connection speeds due to the age of the modem. I've tried 2 different DOCSIS3.1 models (Netgear CM1200 and Motorola MB8611) and both have the same problem. They both connect and provide higher speeds BUT disconnect/reconnect randomly (several times a day) resulting in no internet for 5 minutes. I've had an Xfinity technician come out and re-wire the cable coming into the house. We still have the same issue.
This post from a couple of years ago captures what we have been experiencing since establishing service: https://forums.xfinity.com/conversations/your-home-network/docsis30-works-31-no-longer-functional/605f901fc264e93e85820b74.
Is there a known functional issue for Xfinity and DOCSIS3.1? Is there anyone who is successfully maintaining a stable connection with DOCSIS3.1 modems? I briefly owned an Aris SB8200 but returned it when the technician told me there was a known issue that Aris and Xfinity were working to resolve. Could this be more widespread? For such a critical service, I'd like a clearer explanation of what the problem is and how it can be resolved. Most support focuses on the "did you make sure your modem is plugged in or please manually restart your modem" level, which hasn't been helpful.
zandor60657
Contributor
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217 Messages
2 years ago
DOCSIS 3.1 isn't the problem, at least not directly. It's probably a line issue. DOCSIS 3.1 modems are backwards compatible with DOCSIS 3.0, but also support signaling modes that 3.0 doesn't. Comcast runs a mixed network with some of both. The 3.0 and 3.1 signaling use different frequencies, so what's probably going on is you have some interference that mostly or only affects the 3.1 frequencies. If you have a 3.1 modem it will use the 3.1 only frequencies and there's nothing you can do about that.
If everything is working properly DOCSIS 3.1 can be very stable. My NetGear CM2050V stayed up so long the uptime counter rolled over and started displaying negative numbers. I'm pretty sure it was more than a year.
Could you post your signal stats? Bonus if you can do it with a DOCSIS 3.1 modem since a 3.0 modem won't report signal problems at 3.1 only frequencies. This post gives you some info on how to do it but it's modem specific: https://forums.xfinity.com/conversations/your-home-network/internet-troubleshooting-tips/602dae4ac5375f08cde52ea0 Be sure to redact any MAC addresses (CM-MAC, etc.) and public IP addresses. The forum regards them as personal information and will block your post if you don't. Also it works much better to cut and paste a table rather than taking a screen shot. The forum does quite well with pasted tables and the result will be more readable.
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rilkeanheart
Visitor
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3 Messages
2 years ago
Hi,
Quick update. I switched back to the DOCSIS 3.1 modem and it was running for nearly a week without any issues. All of a sudden, today it started losing connections again. This time it's multiple times per hour. Here is the latest snapshot of the connection details. In addition, I confirmed that the new coax line that the technician ran goes straight from the junction box on the side of the garage to my cable modem. I'm not sure if there's a way for me to check anything between my house and the junction box on the street. Let me know if additional information would be helpful.
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rilkeanheart
Visitor
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3 Messages
2 years ago
Some additional notes on things I can see with the connection details:
1. The frequencies used by the channels does not seem to approach 1GHZ
2. The downstream channel using OFDM PLC for modulation seems to have a VERY high number of correctable packets.
3. When I check the event log I see A LOT of T3 time-outs (alternating between SYNC Timing Synchronization failures and No Ranging Response received:
Example:
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user_914658
Visitor
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17 Messages
2 years ago
I had to switch back to the Xfinity XB8. I'm in NH and I was getting similar issues with my MB8611. One thing to note is that you have Docsis 3.1 only on your downstream channels, channel 32. OFDM is part of Docsis 3.1. You only have Docsis 3.0 on the upload. It's a huge difference I noticed between my MB8611 and the XB8. The XB8 I have has 4 QAM channels and 1 OFDMA channel on the upload. The 8611 only had the 4 QAM channels.
My issue was slow upload speeds and also a lot of packet loss every single day. Once I switched to the XB8 and put it in bridging mode, the issues went away. I'm very unhappy about having to pay an extra $15/month for a Comcast modem because they can't properly provision customer owned equipment to be stable and with the advertised speeds.
Also adding that I had opened up a case with Motorola and they sent me a replacement modem. Same issue with original and replacement modem.
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