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Intermittent Drops - T3 Time outs

Regular Visitor

Intermittent Drops - T3 Time outs

Hoping others who may have similar issues are able to help me:


I've been paying for gigabit service.  I have my own cable modem (a netgear cm1200) and use google wifi as my router.  For the last couple of months, I have been getting intermitten internet drops that last anywhere from 1 -5 minutes.   It can happen as few as a couple of times in one day, and as many as a dozen times in a day.  It has made working from home extremely challenging as I remote into my employers system using Cisco Worspace, and the connection kicks me frequently.


I've been looking at the error logs in my router and I seem to be getting T3 and T4 timeouts.  I checked the wiring inside my house and it looks good.  It's a single cable from outside my house that goes into the router - no splitters at all.  The cable outside my house looks a little banged up.


Here's the issue - I've tried reaching out to Comcast support, and it's been a nightmare.  All that happens is that they reset my router.  A tech came out right before the whole Covid 19 pandemic started and he said that the signal seemed fine.  Suggested I swap out the router/replace it with the xfinity gateway.  Anyone having similar issues?




Re: Intermittent Drops - T3 Time outs

What do the modem's signal stats look like ? 


Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

What is the exact make and model number of the modem ?

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Regular Visitor

Re: Intermittent Drops - T3 Time outs

Netgear CM1200 -Nighthawk Multi-Gig Modem.


Here's the signal info:


Frequency start Value
This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.
Starting Frequency
Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 525000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Security Enabled BPI+
IP Provisioning Mode Honor MDD honorMdd(4)
Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 13 525000000 Hz 5.1 dBmV 40.8 dB 0 0
2 Locked QAM256 10 507000000 Hz 5.4 dBmV 41 dB 0 0
3 Locked QAM256 11 513000000 Hz 5.3 dBmV 40.9 dB 0 0
4 Locked QAM256 12 519000000 Hz 5 dBmV 40.9 dB 0 0
5 Locked QAM256 14 531000000 Hz 5 dBmV 40.8 dB 0 0
6 Locked QAM256 15 537000000 Hz 5.1 dBmV 40.8 dB 0 0
7 Locked QAM256 16 543000000 Hz 5.2 dBmV 40.7 dB 0 0
8 Locked QAM256 17 549000000 Hz 5.4 dBmV 40.6 dB 0 0
9 Locked QAM256 18 555000000 Hz 5.6 dBmV 40.8 dB 0 0
10 Locked QAM256 19 561000000 Hz 5.6 dBmV 40.7 dB 0 0
11 Locked QAM256 20 567000000 Hz 5.5 dBmV 40.6 dB 0 0
12 Locked QAM256 21 573000000 Hz 5.3 dBmV 40.5 dB 0 0
13 Locked QAM256 22 579000000 Hz 5.2 dBmV 40.6 dB 0 0
14 Locked QAM256 23 585000000 Hz 5.2 dBmV 40.5 dB 0 0
15 Locked QAM256 24 591000000 Hz 5.4 dBmV 40.5 dB 0 0
16 Locked QAM256 25 597000000 Hz 5.9 dBmV 40.6 dB 0 0
17 Locked QAM256 26 603000000 Hz 6 dBmV 40.6 dB 0 0
18 Locked QAM256 27 609000000 Hz 6.2 dBmV 40.6 dB 0 0
19 Locked QAM256 28 615000000 Hz 6.1 dBmV 40.5 dB 0 0
20 Locked QAM256 29 621000000 Hz 6.1 dBmV 40.5 dB 0 0
21 Locked QAM256 30 627000000 Hz 5.9 dBmV 40.5 dB 0 0
22 Locked QAM256 31 633000000 Hz 6 dBmV 40.6 dB 0 0
23 Locked QAM256 32 639000000 Hz 6.6 dBmV 40.7 dB 0 0
24 Locked QAM256 34 645000000 Hz 7 dBmV 40.8 dB 0 0
25 Locked QAM256 35 651000000 Hz 7.6 dBmV 40.9 dB 0 0
26 Locked QAM256 36 657000000 Hz 8.1 dBmV 41.1 dB 0 0
27 Locked QAM256 37 663000000 Hz 8.2 dBmV 41 dB 0 0
28 Locked QAM256 38 669000000 Hz 8.1 dBmV 41 dB 0 0
29 Locked QAM256 39 675000000 Hz 8 dBmV 40.5 dB 0 0
30 Locked QAM256 40 681000000 Hz 7.8 dBmV 40.8 dB 0 0
31 Locked QAM256 41 687000000 Hz 8.3 dBmV 41 dB 0 0
32 Not Locked Unknown 0 0 Hz 0.0 dBmV 0.0 dB 0 0
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 36500000 Hz 44 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 30100000 Hz 43.3 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 23700000 Hz 42.3 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 17300000 Hz 41 dBmV
5 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
Downstream OFDM Channels
Channel Lock
Modulation /
Profile ID
Frequency Power SNR /
Active Subcarrier
Number Range
1 Locked 0 ,1 ,2 ,3 33 693000000 Hz 9.1 dBmV 40.4 dB 1108 ~ 2987 66503597 8865565 0
2 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 0
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked 0 0 0 Hz 0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
Extended Upstream Transmit Power
Enable Extended Upstream Transmit Power
Current System Time:Sun Jun 07 18:07:52 2020
System Up Time:01:43:09
Regular Visitor

Re: Intermittent Drops - T3 Time outs

So for what it's worth, I spent an hour with Comcast customer support yesterday.  They reset the cable modem for the 100th time.  They can see there's an issue and told me they would send a tech to see if there is an issue with the cable outside my house.  When we got to the point where they were going to schedule the tech, it turns out that they can't because of Covid-19 or so they claim.  Confusingly, they claimed that someone would reach out to me within 24 hours to schedule the visit seperately.  As I expected, I never heard back.


It must be nice to be a monopoly.

New Poster

Re: Intermittent Drops - T3 Time outs

@Erdosain any luck with CM1200 & Comcast ? I am also facing the same issue.  Comcast scheduled a tech to look into it. He/She will come next week.  

Regular Visitor

Re: Intermittent Drops - T3 Time outs



Yes, it took two tech visits (one in February and one in July), but it looks like Comcast finally resolved the issue.  The wiring inside the house was fine, but there seems to have been an issue with the connection to the line at the cable box itself.   Since that was fixed I have had no more drops.  My supposedly gigabit connection, however, caps out at around 510Mpbs (hardwired to the cable modem for testing).   I've reached out to Comcast about the speeds, but at this point I'm just happy to have reliable internet - regardless of speed.


One thing I learned in this whole 5 month ordeal (hard to believe it was this long); do not believe the tech when they blame your cable modem or router.  I ended up swapping both out, and needlessly spending over $500 to do so (I admiteddly got a nicer cable modem and air mesh system than I previously had) when the problem was with the line, as I had told the first tech to begin with.  I complained to Comcast, who has made no effort to even provide a credit for almost half a year of terrible service. 


Good luck with it! 

New Poster

Re: Intermittent Drops - T3 Time outs

@Erdosain Interesting you mention this. I actually just spent a couple of hours with the Google Nest wi-fi folks. I thought it was definitely the google nest wi-fi router that was giving me issues until I read your post. I was having weird issues with Wi-fi being slow, my work VPN disconnecting/reconnecting, and just overall issues that one should not experience with 1G speeds. I thought it was the google router at first, but we ran some diagnostics with the google folks and they mentioned that my modem was dropping packets to the router. I also have the Netgear Nighthawk CM1200 Modem and I think maybe that's the issue here, but seems like it could be the line as well? 


Here are my troubleshooting steps. I hooked up a LAN cable to a Port on the modem and hooked it up to my laptop. I ran a continous ping without modifing the packet size (default 32 bytes) and I was  actually surprised to see timeouts to my default gateway. I was also seeing packets with 175ms of latency at times. That should not be the case if you're directly plugged in (timeouts aside).  This is when the Modem actually worked. I had to hard reset the whole modem (tiny button on the back of the modem) and hard reset each device in my Google Nest Wi-fi system (mesh). For now everything seems to be working fine, however, this is now the third time in the last few months that I had to do this same process. I'm sure the issue is going to come back because it always does after a few days after doing the same exact things. Wi-fi starts behaving weirdly and we start seeing issues with the connectivity, especially early in the morning. Even though everything seems to be working, I also tried connecting a cable directly from my laptop to an empty port on the modem and I didn't even get an IP (even though the link on the modem showed to be green and the wi-fi is working as well). The Google tech mentioned it could be the modem or more likely a problem with the line so I'm going to give Comcast a call today and see if a tech can come out and take a look. 


Question: Did you ever swap out your modem with the one Comcast provides? I spent some hard earned money on the google-mesh wifi and the Nighthawk modem. Both were highly recommended, and the modem was compatible with Comcast services as per their site. I'm wondering if I should first swap out the modem to see if it makes a difference or just ask Comcast to come out and check the line (I suspect I'll have to prove that Comcast service is flawed and dig in for a battle). I mean if there are dropped packets coming from the modem, I suspect the issue is on the modem/comcast side of things and not the Google wi-fi system. Also, what products did you end up going with (cable modem and router)?