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jasqid
Fiber In Your Diet?

join:2002-04-02
East Palestine, OH

New SB6121 - Now connection isnt as reliable

For the last 8 years or so I was using a SB5120. Had no issues whats so ever. Just over a week ago I picked up a SB6121 because I wanted D3 compatible modem. (My area is D3 compliant).

I provisioned the modem myself through the walledgarden. It was quite easy. It rebooted several times after a firmware download and then a conf download.

WHat I have noticed now is that the modem is rebooting randomly and causing my VOIP conversations to fail. It seems to reboot when I am on a call. It has happened 3 times during a call. (Never with my old modem). I have also noticed that since the last reboot that happened on Sept 1, that the upstream communication in no longer bonded (Green light instead of blue).

Signals:
Down:
Channel ID 197 198 199 200
Frequency 591000000 Hz 597000000 Hz 603000000 Hz 609000000 Hz
Signal to Noise Ratio 36 dB 36 dB 35 dB 36 dB
Downstream Modulation QAM256 QAM256 QAM256 QAM256
Power Level
The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
9 dBmV 9 dBmV 9 dBmV 9 dBmV

UP:
Channel ID 1
Frequency 18900000 Hz
Ranging Service ID 7707
Symbol Rate 2.560 Msym/sec
Power Level 35 dBmV
Upstream Modulation [3] QPSK
[2] 16QAM

Ranging Status Success

Channel ID 197 198 199 200
Total Unerrored Codewords 6709087111 6703102090 6703102268 6703102006
Total Correctable Codewords 20 0 0 0
Total Uncorrectable Codewords 586 513 480 526

Firmware:
Model Name: SB6121
Vendor Name: Motorola
Firmware Name: SB_KOMODO-1.0.6.6-SCM00-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.
Hardware Version: 5.0
Serial Number: xxxxxxxxxxxxxxxx
Firmware Build Time: Apr 17 2012 15:09:37

My Logs have 5 listings for "cable modem rebooted due to power reset" or a T4 timeout.


andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL

You signals are good to slightly too strong. Your upstream is actually a bit low. It's recommended to be in the 40's.

There have been issues lately with the 612x series and T4 timeouts. You don't have upstream bonding, so I'm a bit surprised you are having those issues, unless there is something else going on preventing you from bonding.



jasqid
Fiber In Your Diet?

join:2002-04-02
East Palestine, OH

My down power has always been 9 to 12. Usually double digits. When I first provisioned the modem I had bonding (Modem lights were all BLUE). I just did a factory reset on it. I'll see what happens.)

I also posted in the CC direct forum to see if they had a recommendation. Most like likely will end up with a tech coming out to adjust the signal. It's been 4 or 5 years since someone has been out here... perhaps due for a checkup.



jasqid
Fiber In Your Diet?

join:2002-04-02
East Palestine, OH
reply to jasqid

Well, factory rest did nothing but clear the logs.

Upon reboot, the downstream was green (non-bonded) and the upstream was blue (bonded), then they switched when the reboot was complete. Down is now blue and up green again.


djlandkpl

join:2007-12-27
Norton, MA
reply to jasqid

Create a post on the Comcast Direct forum. ComcastSteve did something to fix my 6121. I was having all kinds of disconnect issues. Now my modem is very stable.



tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
Reviews:
·Comcast
reply to jasqid

said by jasqid:

My Logs have 5 listings for "cable modem rebooted due to power reset" ....

check theat the power supply is the correct one, plugged in correctly at both ends and nothing has damaged the wire or is pulling it loose.
Also, I believe most T4's are associated with upstream noise, given your fairly low power output, you COULD be seeing issues at that end.
You'll need to call in and ask what the UPSTREAM SNR is like.

Other than a somewhat high downstram power nothing about the signals jumps out as bad.


Cozmo85

@comcast.net

Go buy a splitter that gives you 7-8db Attenuation. It will bring your upstream up and your downstream down. It could fix your problems.


JPnATL

join:2011-11-16
Bethlehem, GA
reply to jasqid

Best to call Comcast and have them come out instead of buying this and that. they will install whatever needs be installed for free.



EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:9
reply to Cozmo85

said by Cozmo85 :

Go buy a splitter that gives you 7-8db Attenuation. It will bring your upstream up

FWIW, that basically only makes the upstream power level figure as read by the modem *look prettier*..


Cozmo85

@comcast.net
reply to JPnATL

While that is the best idea, not everyone has time for comcasts 4 hour window. For five dollars you might fix your problem.


bman212121

join:2005-06-09
reply to Cozmo85

What EG said.

Basically all your doing with an attenuator is adding another barrier for the signal to try to make its way through. It would be like putting a box around your wireless access point and thinking you're getting better signals from it.

It would help if the amount of incoming signal is too high for the modem to even operate, but at 9dBmV that really isn't the case. The modem can operate at up to 15dBmV before it has too strong of a signal.

»Comcast High Speed Internet FAQ »What should my Signal Levels be?

@OP: The T4 timeout issue seems to be very complicated. They are working on a new firmware to see if they can get it under control. I can assure you that even with "perfect" signal levels T4 timeouts are still an issue. I have 0dBmV downstream on all four channels, 37dB SNR, and 43 - 44dBmV upstream power levels. What I've noticed is that when my modem is going to T4 the upstream numbers creep up and can hit the 52dBmV mark. 8dBmV is quite a swing for the modem to be having under normal conditions. My drop is about 1 year old now and worked flawlessly for 10 months and hasn't been touched, so cabling is basically ruled out IMO. To further backup that theory some of my worst issues with T4 when we have perfect weather conditions. (mid 70's, partly sunny skies) It has been pouring rain and thundering all morning and I have a 14 hour uptime right now. It hasn't rained in about 3 days prior and yesterday the modem was lucky to go 3 hours. (If it were a loose end or something wrong with the cable rain certainly wouldn't help it.)

The best guess I have is something in the software makes the modem think that it needs to turn up the power levels even more causing it to keep rising until it finally goes high enough it drops out. It could even be something like one upstream turns itself up slightly causing an issue for another upstream so that one turns itself up, then the 3rd one does, and by then the first one isn't happy anymore and the cycle repeats. It will be interesting if they find a fix and if we can get an explanation of what was the cause.


andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL

Given that these channels are right next to each other, it depends on how accurate the modem is transmitting the frequency, and how well it is preventing adjacent channel interference. There may be too much tolerance, or many modems may be out of tolerance given that it was never really tested until now. The specs themselves could even require a tweak now that it's being used in the real world.

What I've found interesting is that when 3-channel upstream gets T4 issues, it seems as if it's always the middle channel having a problem. That could be a modem firmware issue, or even the CMTS's firmware/software.


bman212121

join:2005-06-09

I can confirm your issues with the middle channel. Any time I've seen an individual channel drop out, it was always the middle one. I wish I could remember from the first time we had channel bonding if it was 2 or 3 channels. We had it almost a year ago before they took it away and at that time there were no issues. I wasn't paying close enough attention when we got it back but there might have been a good month or so where I had it the 2nd time and it wasn't causing issues. Perhaps you are onto something about what frequencies were being used and maybe that is what changed and is now causing all of the issues.


travelguy

join:1999-09-03
Santa Fe, NM
reply to bman212121

said by bman212121:

They are working on a new firmware to see if they can get it under control.

It would be nice if there were some "official" indication that there was a problem and that they were working on it. The problem with that of course (as evidenced by this thread) is that everyone would think their problem is related which clearly isn't the case.


JJJohnson

join:2001-08-25
Fort Collins, CO
reply to jasqid

Almost identical to my experience. I recently "upgraded" from an SB5120 to an SB6120 and the connection has been much less reliable.



trythisfirst

@comcast.net
reply to JPnATL

said by JPnATL:

Best to call Comcast and have them come out instead of buying this and that. they will install whatever needs be installed for free.

Inside wiring may generate a 49.95 service charge if you do not subscribe to the maintenance plan.


trythisfirst

@comcast.net
reply to Cozmo85

said by Cozmo85 :

While that is the best idea, not everyone has time for comcasts 4 hour window. For five dollars you might fix your problem.

local appointment windows in my area. 8-9, 8-10, 10-12, 1-3, 3-5,and 5-7. No four hour windows for residential service here...

mclasser

join:2011-12-12
reply to jasqid

I used an SB6121 for about a month after my trusty D2 modem of 6 years bit the dust. I quickly learned why many people say the 6121 is so sensitive to signal fluctuations and line noise. The modem signal levels were on the lower ends of the acceptable windows. After about 2 weeks, the thing began having T3/T4 timeouts and frequent restarts. I jumped ship and bought a Zoom 5341J. This modem has been working flawlessly ever since. The signal levels have all increased with this modem and are solidly in the acceptable windows. The 8 downstream channels vs the 4 in the 6121 are also a definite plus.