Community Forum

downstream OFDM SNR????

Highlighted
Frequent Visitor

downstream OFDM SNR????

I just connected a new netgear CM1000V2 because my old zoom modem had to be rebooted about once a day to to lock-up (would lose connection completely).  Netgear seems to have solved the loss of connectivity.  I pay for 300mbps plan and comcast speed test shows my downstream is 200mbps +/-.  House desktops and TVs all hardwired with home run connections to aggregating PCs<->Gig-E switch <-> router<->cblmodem.  After a lot of reading-up on modem signal levels, I am questioning my downstream OFDM SNR - its 30-31 db.  All other downstream channels are 35-39 SNR. Power levels look good (downstream running 0-4dbmv). Uncorrectables are very small.

 

 

 

 

Highlighted
Frequent Visitor

Re: downstream OFDM SNR????

Tried to insert image of modem status page with channels/levels etc, no go. So, below is a text paste.... See RED line near bottom.

 

Also, I tried plugging coax enetering home straight to modem to bypass splitter that splits TV/internet and there was no improvement to SNR or download speed.

 

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

<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 579000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Security Enable BPI+
IP Provisioning Mode Honor MDD IPv6 only

<tabindex=-1>Downstream Bonded Channels</tabindex=-1>
Channel Lock Status Modulation Channel ID Frequency Power SNR / MER Unerrored Codewords Correctable Codewords Uncorrectable Codewords
1 Locked QAM256 13 579000000 Hz 1.0 dBmV 38.1 dB 3253066445 0 0
2 Locked QAM256 10 561000000 Hz 1.5 dBmV 38.1 dB 3252151242 0 0
3 Locked QAM256 11 567000000 Hz 1.4 dBmV 38.1 dB 3252155575 0 0
4 Locked QAM256 12 573000000 Hz 1.4 dBmV 38.1 dB 3252158984 0 0
5 Locked QAM256 14 585000000 Hz 1.2 dBmV 38.0 dB 3252162445 0 0
6 Locked QAM256 15 591000000 Hz 1.1 dBmV 38.0 dB 3252166076 0 0
7 Locked QAM256 16 597000000 Hz 0.4 dBmV 37.7 dB 3252169819 0 0
8 Locked QAM256 17 603000000 Hz 0.0 dBmV 37.6 dB 3252174714 0 0
9 Locked QAM256 18 609000000 Hz -0.3 dBmV 37.4 dB 3252182066 0 0
10 Locked QAM256 19 633000000 Hz 1.2 dBmV 37.3 dB 3252184269 13 19
11 Locked QAM256 20 615000000 Hz -0.4 dBmV 37.2 dB 3252189855 0 0
12 Locked QAM256 21 621000000 Hz -0.1 dBmV 37.3 dB 3252192232 0 0
13 Locked QAM256 22 627000000 Hz 1.1 dBmV 37.4 dB 3252196705 0 0
14 Locked QAM256 23 639000000 Hz 1.9 dBmV 37.2 dB 3252178876 3 31
15 Locked QAM256 24 645000000 Hz 1.3 dBmV 37.1 dB 3252179190 6 28
16 Locked QAM256 26 651000000 Hz 1.2 dBmV 36.8 dB 3252174005 7 28
17 Locked QAM256 27 657000000 Hz 0.4 dBmV 36.6 dB 3252191404 12 28
18 Locked QAM256 28 663000000 Hz -0.1 dBmV 36.4 dB 3252193947 8 31
19 Locked QAM256 29 669000000 Hz 0.2 dBmV 36.3 dB 3252197864 10 30
20 Locked QAM256 30 675000000 Hz 0.3 dBmV 35.8 dB 3252202244 12 28
21 Locked QAM256 31 681000000 Hz 0.8 dBmV 36.1 dB 3252203872 11 30
22 Locked QAM256 32 687000000 Hz 1.3 dBmV 36.0 dB 3252209285 10 28
23 Locked QAM256 33 693000000 Hz 2.4 dBmV 36.0 dB 3252212822 14 26
24 Locked QAM256 34 699000000 Hz 3.1 dBmV 36.1 dB 3252217002 7 26
25 Locked QAM256 35 705000000 Hz 3.9 dBmV 36.4 dB 3252220387 0 0
26 Locked QAM256 36 711000000 Hz 3.9 dBmV 36.2 dB 3252224000 0 0
27 Locked QAM256 37 717000000 Hz 2.9 dBmV 36.1 dB 3252227924 0 0
28 Locked QAM256 38 723000000 Hz 2.7 dBmV 36.0 dB 3252230639 0 0
29 Locked QAM256 39 729000000 Hz 2.2 dBmV 35.8 dB 3252236420 0 0
30 Locked QAM256 40 735000000 Hz 2.7 dBmV 35.9 dB 3252238115 0 0
31 Locked QAM256 41 741000000 Hz 2.6 dBmV 35.7 dB 3252241795 0 0
32 Not Locked Unknown 0 0 Hz 0.0 dBmV 0.0 dB 0 0 0

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status Modulation Channel ID Frequency Power
1 Locked ATDMA 81 36500000 Hz 45.5 dBmV
2 Locked ATDMA 82 30100000 Hz 45.5 dBmV
3 Locked ATDMA 83 23700000 Hz 44.0 dBmV
4 Not Locked Unknown 0 0 Hz 0.0 dBmV
5 Not Locked Unknown 0 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Hz 0.0 dBmV

<tabindex=-1>Downstream OFDM Channels</tabindex=-1>
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier Number Range Unerrored Codewords Correctable Codewords Uncorrectable Codewords
1 Locked 0, 1, 2, 3 25 780000000 Hz 2.8 dBmV 31.0 dB 1108 ~ 2987 346999323 318918359 3906
2 Not Locked 0 0 0 Hz 6.8 dBmV 0.0 dB 0 ~ 4095 0 0 0

<tabindex=-1>Upstream OFDMA Channels</tabindex=-1>
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked Unknown 0 0 Hz 0 dBmV
2 Not Locked Unknown 0 0 Hz 0 dBmV

Current System Time: Mon May 18 10:03:23 2020
System Up Time: 19:53:27

 

 

 

                     
                     
Highlighted
Expert

Re: downstream OFDM SNR????

It is a known issue that some makes and models of modem's measuring mechanisms do not read the power level and the SNR of the OFDM channel accurately.



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
Frequent Visitor

Re: downstream OFDM SNR????

Do we have a list of those known modems?? Based on prior posts on this forum, seems other CM1000 modems report in the correct range. See prior post https://forums.xfinity.com/t5/Your-Home-Network/Connectivity-Issues-with-Netgear-CM1000/m-p/3333159  where they show 39db on the OFDM channel. I think I'm running low at 30db??

 

Also, in my event log, I only get nags about OFDM. Not sure what they tell us if anything:

Time Priority Description
2020-05-18, 12:52:26 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:51:42 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:50:29 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:49:52 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:48:28 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:48:07 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:45:47 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:45:15 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:42:11 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:41:14 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:40:56 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:40:32 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
 
Highlighted
Frequent Visitor

Re: downstream OFDM SNR????

Well, tried comcast phone support with no result other than hearing the script, so did more debugging by reading lots of posts for CM1000 users seeing what their levels were before/after issues, developed a list of things to check, etc.

 

Rehung 70' coax run in basement to move 12"+ away from AC power lines, removed 'Y' splitter that splits TV/Modem to boost signal a bit and turned off all options on linksys router to strip/simplify everything. Performace went from 200mbps to 385mbps which is a little higher than advertised plan speed. Success.

 

Case closed for now. Thanks to all who helped and answered PMs regarding their case as it helped me move forward with debugging.