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Chet9

join:2012-07-05
Jackson, MS

[Connectivity] T3/T4 dropouts, signal appears to be within spec.

I moved into the house November 2011 and have had no connection problems until about 3 weeks ago, when I came into the living room after getting up one morning and saw something up with the lights on the cable modem (SB6120). Under normal operation, Power, Send, Receive, and Online are all solid green, and Link blinks blue rhythmically. On this particular morning, all the LEDs were off, except Power, which was solid blue. I watched it for some time, and it never resolved itself, so I power cycled, and the modem went right back to normal after its regular boot-up liturgy. Unfortunately, I've been having frequent dropouts every since.

Modem info:
Model Name: SB6120
Vendor Name: Motorola
Firmware Name: SB612X-1.0.3.3-SCM00-NOSH
Boot Version: PSPU-Boot 1.0.0.4m1
Hardware Version: 3.0
 

After about a week of this, I started to investigate. The modem status page told me I have four bonded downstream channels and a single upstream channel. The downstream channels were showing signal levels around -3 dBmV, and upstream was right at 57 dBmV.

I don't have television service, and the modem is the only thing using the cable, so I went up into the attic and replaced a splitter with a straight-though coupler. This brought the downstream signal levels right to 0 and the upstream level to about 49 or 50 dBmV. But the dropouts have continued.

Yesterday I went out to the pole and followed the line all the way to the termination box outside the house, then following the single line from the termination box up the side of the house and into the gable vent in the roof. I went into the attic, disconnected the cable from the first connector in the line, and connected the modem. Now I'm seeing downstream of about 2 dBmV and upstream of about 49-50 dBmV. Still having dropouts.

At every step along the way, the SNR across all 4 downstream channels has held solid at 38 dB.

Here's my signal page:
+------------------------------------------------------------------------------+
| Downstream                   | Bonding Channel Value                         |
|------------------------------+-----------------------------------------------|
| Channel ID                   | 205       | 206       | 207       | 208       |
|------------------------------+-----------+-----------+-----------+-----------|
| Frequency                    | 591000000 | 597000000 | 603000000 | 609000000 |
|                              | Hz        | Hz        | Hz        | Hz        |
|------------------------------+-----------+-----------+-----------+-----------|
| Signal to Noise Ratio        | 38 dB     | 39 dB     | 38 dB     | 38 dB     |
|------------------------------+-----------+-----------+-----------+-----------|
| Downstream Modulation        | QAM256    | QAM256    | QAM256    | QAM256    |
|------------------------------+-----------+-----------+-----------+-----------|
| Power Level                  |           |           |           |           |
|                              |           |           |           |           |
| The Downstream Power Level   |           |           |           |           |
| reading is a snapshot taken  | 2 dBmV    | 2 dBmV    | 2 dBmV    | 2 dBmV    |
| at the time this page was    |           |           |           |           |
| requested. Please            |           |           |           |           |
| Reload/Refresh this Page for |           |           |           |           |
| a new reading                |           |           |           |           |
+------------------------------------------------------------------------------+
 
                +---------------------------------------------+
                | Upstream            | Bonding Channel Value |
                |---------------------+-----------------------|
                | Channel ID          | 2                     |
                |---------------------+-----------------------|
                | Frequency           | 31000000 Hz           |
                |---------------------+-----------------------|
                | Ranging Service ID  | 7829                  |
                |---------------------+-----------------------|
                | Symbol Rate         | 2.560 Msym/sec        |
                |---------------------+-----------------------|
                | Power Level         | 49 dBmV               |
                |---------------------+-----------------------|
                |                     | [3] QPSK              |
                | Upstream Modulation | [2] 16QAM             |
                |                     | [3] 64QAM             |
                |                     |                       |
                |---------------------+-----------------------|
                | Ranging Status      | Success               |
                +---------------------------------------------+
 
+------------------------------------------------------------------------------+
| Signal Stats (Codewords) | Bonding Channel Value                             |
|--------------------------+---------------------------------------------------|
| Channel ID               | 205        | 206        | 207        | 208        |
|--------------------------+------------+------------+------------+------------|
| Total Unerrored          | 414084481  | 414084690  | 414084780  | 414084869  |
| Codewords                |            |            |            |            |
|--------------------------+------------+------------+------------+------------|
| Total Correctable        | 46         | 1          | 1          | 0          |
| Codewords                |            |            |            |            |
|--------------------------+------------+------------+------------+------------|
| Total Uncorrectable      | 1468       | 1417       | 1470       | 1525       |
| Codewords                |            |            |            |            |
+------------------------------------------------------------------------------+
 

And error logs:
+---------------------------------------------------------------------------------- ----------------------------+
|Time    |Priority  |Code  |Message                                                                            |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|17:52:14|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jan 01  |          |      |Unicast Ranging Received Abort Response - initializing                             |
|1970    |3-Critical|R07.0 |MAC;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|00:00:17|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jan 01  |          |      |Cable Modem Reboot due to T4 timeout                                               |
|1970    |6-Notice  |      |;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;        |
|00:00:12|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Unicast Ranging Received Abort Response - initializing                             |
|2012    |3-Critical|R07.0 |MAC;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|17:47:54|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Received Response to Broadcast Maintenance Request, But no Unicast Maintenance     |
|2012    |3-Critical|R04.0 |opportunities received - T4 time                                                   |
|17:47:54|          |      |out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|17:47:24|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |DCC-ACK not                                                                        |
|2012    |4-Error   |C401.0|received;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|17:47:15|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|17:47:15|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jan 01  |          |      |Unicast Ranging Received Abort Response - initializing                             |
|1970    |3-Critical|R07.0 |MAC;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|00:00:18|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jan 01  |          |      |Cable Modem Reboot due to T4 timeout                                               |
|1970    |6-Notice  |      |;CM-MAC=[----REDACTED---];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;        |
|00:00:12|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Unicast Ranging Received Abort Response - initializing                             |
|2012    |3-Critical|R07.0 |MAC;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|09:09:09|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Received Response to Broadcast Maintenance Request, But no Unicast Maintenance     |
|2012    |3-Critical|R04.0 |opportunities received - T4 time                                                   |
|09:09:08|          |      |out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|09:08:38|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |DCC-ACK not                                                                        |
|2012    |4-Error   |C401.0|received;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|09:08:29|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|09:08:29|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jan 01  |          |      |Cable Modem Reboot due to T4 timeout                                               |
|1970    |6-Notice  |      |;CM-MAC=[----REDACTED---];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;        |
|00:00:12|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Lost MDD                                                                           |
|2012    |5-Warning |T202.0|Timeout;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0; |
|01:45:41|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |Received Response to Broadcast Maintenance Request, But no Unicast Maintenance     |
|2012    |3-Critical|R04.0 |opportunities received - T4 time                                                   |
|01:45:39|          |      |out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;     |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 05  |          |      |SYNC Timing Synchronization failure - Loss of                                      |
|2012    |3-Critical|T05.0 |Sync;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;    |
|01:45:17|          |      |                                                                                   |
|--------+----------+------+---------------------------------------------------------------------------------- -|
|Jul 04  |          |      |No Ranging Response received - T3                                                  |
|2012    |3-Critical|R02.0 |time-out;CM-MAC=[----REDACTED---];CMTS-MAC=[----REDACTED---];CM-QOS=1.1;CM-VER=3.0;|
|22:11:49|          |      |                                                                                   |
+---------------------------------------------------------------------------------- ----------------------------+
 

So it looks like everything is within spec, but I'm still getting these dropouts. It doesn't seem like they are tied to any specific usage pattern (i.e. heavy loads) because they occur at night when there's no traffic.

One other thing I will mention is that I no longer have the original power adapter that came with the modem, and so I am using a "universal" type adapter that is +12 v and 1200 mA. The power rating on the modem itself says +12 v, .75 A. I used a multimeter to confirm that the universal adapter is providing +12 v and .75+ A at the tip (and I have been using it ever since I moved into this house) but I mention it just in case.

I have also tried moving the modem to different locations and plugging it into different outlets.

I'm looking for suggestions of things I can do to rectify the problem without contacting Comcast. This includes possible remedies within the outdoor termination box (which I am in the process of figuring out how to open non-destructively).

Can anyone suggest anything? I've tried everything I can think of. Thanks!


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

1 edit

Re: [Connectivity] T3/T4 dropouts, signal appears to be within s

At 57 dB the upstream power level is way out of spec. Are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured ?

if there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then putting them back together again, then perhaps it's best to book a tech visit to investigate and correct.


Chet9

join:2012-07-05
Jackson, MS
reply to Chet9

Thanks for the reply, but as I explained in the OP, I did eliminate all splitters, connectors, and cable bends, so the modem is now connected directly to the outside termination box. I am getting +2 dBmV down, +49 dBmV up, and SNR 38 dB. As I understand it, this is within spec. But I'm still getting dropouts as reflected in the logs posted in the OP.

Also, I am looking for things to try that do not include booking a tech visit or otherwise contacting Comcast.



flwpwr

@comcast.net

49 with no splitters is not normal.

Things you can try:
Go to your comcast shop, or stop a tech you see out and about and ask for a piece of cable long enough to run temporarily from your dmarc [ground block where the drop comes in at/near the house] to your modem basically bypassing your in house wiring. Check the modem levels then, if they are in the return range of 43 then your house wiring is suspect, if its still 48/49 the drop or plant has some sort of issue and a tech visit is likley the only way to fix it. You can try store bought cable but a machine puts the ends on those and it does not certify them in any way, often I find thermal regression or shorts just looking at them and there is a chance you will buy solid core which is bad instead of foam core. If you know how to ensure you do not, then have at walmart or home depot.



tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
Reviews:
·Comcast
reply to Chet9

Can you call and ask about your upstream SNR, the entries in the logs look like a possible noise problem.

You say you've tried different outlets which means there must be additional splitters involved, maybe hidden in the walls, which might imply the cable wiring (or parts of it) is as old as the house and may have hidden damage.
I'm certainly not recommending you break in to the terminal box but having/testing a direct line from the ground block might give better results (you would learn something just from the experiment)
Not sure I understand your reluctance to call in a ComCast tech, part of your bill covers part of the cost for a trained professional with tools, and most don't bite.


Chet9

join:2012-07-05
Jackson, MS
reply to Chet9

Thanks guys. I didn't know that 49 with no splitters is not normal, so that's helpful.

Some points of clarification may be in order:

First, unless I'm misunderstanding, I believe that in my current configuration, the modem is connected directly to the outside box where the drop comes in. There is a cable coming in from the pole, and running to the box. A second cable runs from the box, and the modem is connected directly to that cable, which appears to be new (the house was renovated in 2009, and the F connector on the cable coming from the box appears to be brand new).

Second, when I said I had tried different outlets, I was referring to electrical outlets, as I have read that sometimes ground loops in the electrical line can cause RF noise that disrupts cable modems.

Third, the reason I do not want to contact Comcast is that they stopped sending me bills nearly a year ago after a series of customer-service deficiencies that were particularly grievous, even for Comcast. I'm not entirely certain that was intentional on their part, and I don't really want to find out.

In light of all that, I think the house cabling probably can be ruled out. In previous locations, connectivity problems have been corrected by a tech replacing connectors and/or splitters inside the box, so I'm inclined to take a look in there and see if that's something I can do myself. Alternately, I can try to test the signal strength on the line coming directly from the pole.

Failing that, it may be time to start looking at DSL. :-(



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

said by Chet9:

Third, the reason I do not want to contact Comcast is that they stopped sending me bills nearly a year ago after a series of customer-service deficiencies that were particularly grievous, even for Comcast. I'm not entirely certain that was intentional on their part, and I don't really want to find out.

You haven't paid for service in a year?
I'm done helping.