A while ago I got Comcast's business service. Semi-idle connections
are get dropped (I haven't really diagnosed this - I just no that it
isn't the client or server but some network in between). However the
second and most obvious issue is that intermittently, the service will
grind to a halt:
--- 8.8.8.8 ping statistics ---
37 packets transmitted, 34 received, 8% packet loss, time 36263ms
rtt min/avg/max/mdev = 398.821/5989.160/14407.055/3808.068 ms, pipe 15
After a modem reboot, it goes normal:
--- 8.8.8.8 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 23.181/23.920/24.298/0.474 ms
This seems to happen about once or twice a day. I can't attribute it
to any type of traffic or number of connections. All of the rest of
the network equipment is the same and the behavior persists when a
computer is plugged directly into the modem. I called Comcast and they
said they didn't see anything even when I was experiencing ridiculous
ping times. I tend to think it's an issue with the 'modem' but I'm not
sure what the issue might be or how to reproduce it when asked to if I
tell them to look at it.
Is this on their DOCSIS service? I've seen the F connector on the back of the CM
introduce noise to the local segment and cause troubles. If so, you need to have them
dispatch and swap the CM with one that doesn't have this issue.
- Jared
If it's one of their new Netgear-branded modems, see if you can get your
tech to dig up an SMC.
We had the same issue. They swapped out one Netgear modem for another
Netgear and the problem continued. The phone techs couldn't see the problem
and kept blaming our equipment. They finally sent out one of the 'senior'
engineers I had worked with before on other jobs. He managed to get a hold
of one of the SMCs from their warehouse. No more issues.
-A
Thanks. The tech said they looked at signal levels when I called and didn't
see anything. I didn't have a baseline at the time (I do now) and assumed
they'd see something there if there was something.
I do have the Netgear. So I'll keep this in mind when I call them again
(assuming it's really not a noise issue) though I'm not sure exactly what
happened here or how I can get them to try the same thing?
I’ve seen this happen before with various cable ISPs. I’d concur with the poster suggesting intermittent noise on the cable segment as a likely culprit. Also if you have a cable modem that binds multiple channels for higher bandwidth this can also be problematic, especially with the noise. Signals will look good to the NOC but it’s not the signal “level" that’s the issue it’s the signal to noise level. Noise has to be measured locally and techs don’t always check SNL.
Also check to see if the packets aren’t actually being dropped but just taking longer than ping is looking for. Also check for out of sequence packets returned. These can indicate flapping of a bonded circuit or the bonded circuit experiencing noise. Try seeing if you disconnect everything and get a straight run to the demarc, with a know and tested out good cable, if the problem doesn’t ever occur. This could indicate noise on the cable in your premise. But I’ve experienced this same problem with noise coming through the demarc. I’ve also seen levels too hot beyond the demarc causing similar problems too.
HTH.
-d
They often say everything looks okay. I can recall one conversation where
the tech said he was talking to my modem and there were no problems all the
way to it. I replied that it was unplugged in my hand because I had done so
to read the serial number to him, so he couldn't be talking to it. Service
did get better after that. 
-R>
Works:
Downstream Channel
Downstream Frequency525000000 Hz561000000 Hz567000000 Hz573000000 Hz579000000 Hz
Lock StatusLockedLockedLockedLockedLocked
Modulation256 QAM256 QAM256 QAM256 QAM256 QAM
Symbol Rate5.360537 Msym/sec5.360537 Msym/sec5.360537 Msym/sec5.360537
Msym/sec5.360537 Msym/sec
Downstream Power 2.2 dBmV 3.8 dBmV 3.0 dBmV 2.9 dBmV 2.9 dBmV
SNR41.2 dBmV40.8 dBmV40.5 dBmV40.9 dBmV41.0 dBmV
Upstream Channel
Upstream Frequency36000000 Hz29400000 Hz22800000 Hz0 Hz
Lock StatusLockedLockedLockedNot Locked
ModulationATDMAATDMAATDMAUnknown
Symbol Rate5120 sym/sec5120 sym/sec5120 sym/sec0 sym/sec
Upstream Power46.2 dBmV46.2 dBmV46.2 dBmV0 dBmV
--- 8.8.8.8 ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9013ms
rtt min/avg/max/mdev = 23.066/27.049/35.627/4.825 ms
Not working:
Downstream Channel
Downstream Frequency525000000 Hz561000000 Hz567000000 Hz573000000 Hz579000000 Hz
Lock StatusLockedLockedLockedLockedLocked
Modulation256 QAM256 QAM256 QAM256 QAM256 QAM
Symbol Rate5.360537 Msym/sec5.360537 Msym/sec5.360537 Msym/sec5.360537
Msym/sec5.360537 Msym/sec
Downstream Power 2.2 dBmV 3.8 dBmV 2.9 dBmV 2.8 dBmV 2.9 dBmV
SNR41.4 dBmV40.8 dBmV40.4 dBmV41.0 dBmV41.3 dBmV
Upstream Channel
Upstream Frequency36000000 Hz29400000 Hz22800000 Hz0 Hz
Lock StatusLockedLockedLockedNot Locked
ModulationATDMAATDMAATDMAUnknown
Symbol Rate5120 sym/sec5120 sym/sec5120 sym/sec0 sym/sec
Upstream Power46.5 dBmV46.5 dBmV46.5 dBmV0 dBmV
--- 8.8.8.8 ping statistics ---
233 packets transmitted, 232 received, 0% packet loss, time 232884ms
rtt min/avg/max/mdev = 23.431/1918.702/8758.161/2017.033 ms, pipe 9
I'm not seeing any big difference in SNR (and only slight differences
in upstream power) and everything else seems to be the same. Though,
since db is logarithmic, .3 might be enough to matter?
Biggest unknown at this point is your upstream SNR. If there is noise ingress somewhere in the plant, then your upstream could be having all kinds of issues.
Robert
Do you also receive an _analog_ television signal from Comcast? How's
the picture? Any ghosting, blurring or white noise? Any difference
between working times and non-working times for your Internet service?
Any difference if you connect directly to their entry cable without
allowing it to touch the cable in your facility?
Regards,
Bill Herrin