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upstream channel power levels too low - what to do.

Frequent Visitor

upstream channel power levels too low - what to do.

 

We are suffering occassional outages and some minor packet loss. Arris tells us the power levels on the upstream channels are too low. Should be 45dBmv, but it's just under. How to adjust this? 

 

Upstream Bonded Channels
Channel Channel ID Lock Status US Channel Type Frequency Width Power
1 84 Locked SC-QAM 38700000 Hz 6400000 Hz 43.8 dBmV
2 81 Locked SC-QAM 19300000 Hz 6400000 Hz 43.5 dBmV
3 82 Locked SC-QAM 25700000 Hz 6400000 Hz 43.5 dBmV
4 83 Locked SC-QAM 32300000 Hz 6400000 Hz 43.3 dBmV
Expert

Re: upstream channel power levels too low - what to do.

They are fine ! An end user can't "adjust" them anyway. Something else is going on. What do the downstream power levels and the SNR's look like ?



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Frequent Visitor

Re: upstream channel power levels too low - what to do.

@EG that’s what Arris support said:

Thank you for providing the information from your Event Log for our review. Based on the messages we see there, it appears that the modem is rebooting and registering for connection with the CMTS periodically. Ranging response errors and timeouts do indicate a probable issue with noise on the upstream which is a symptom of insufficient upstream power levels. We would recommend that you contact your service provider to make the appropriate adjustments to those levels for you. If they advise that the levels they are sending are within the range (of 45-51 dBmV), this could indicate a possible issue with a faulty cable splitter or a coaxial cable line in your area in need of maintenance.
Expert

Re: upstream channel power levels too low - what to do.

It doesn't truly matter what any manufacturer states. They are frequently incorrect.... What truly matters is the cable ISP's (in this case, Comcast's) system specs;

 

Downstream Power Levels: -8dBmV to  +10dBmV

Downstream Signal to Noise Ratio (SNR):  >35dB 

Upstream Power Level:  +25dBmV to +54dBmV

Upstream Signal to Noise Ratio (uSNR): >31dB  

Upstream Receive Power: -2dBmV to +2dBmV

 

But if you are having "outages", then obviously something is going on. As I stated, the upstream power (at that snapshot / moment in time) was o/k. But it could be fluctuating out of spec intermittently. The modem's error log entries would record these events but you did not post them here for US to see..

 

You also haven't yet posted the downstream stuff that I asked for..

 

Also, is this with a WiFi connection ?



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Re: upstream channel power levels too low - what to do.

@EG First, thank you so much for your help. Highly appreciated. It's really difficult with Comcast customer support. 

 

See below for full set of downstream and upstream values. I am also posting the event log of the last two days (did a full reset of the modem two days ago on advice by Comcast support). I put "xx" for the modem's Mac address.

 

Yes, it's a Wifi connection. Wifi is totally stable (0% packet loss over multiple days pinging the router at 10.0.1.1 or the modem at 192.168.100.1).  Here are the results from pinging various locations for 24+ hours that I ran in the last two days:

 

 

ping 10.0.1.1 (my router) 0% packet loss

ping 192.168.100.1 (the modem) 0% packet

ping 24.130.142.58 (my public IP) 0.1% packet loss

ping 24.130.142.1 (Comcast router) 0.1% packet loss

ping 8.8.8.8 (google) 0.1% packet loss

ping 2001:4860:4860::8888 (google ipv6) 0.1% packet loss

 

Noteworthy, there was not a single longer outage during that time, but every 1000 attempts or so ping returns  "request timeout for icmp_seq: network is down". And it happens between the modem (192.168.100.1 and my public IP address 24.130.142.58. By the way, does pinging 24.130.142.58 means pinging the modem or pinging a piece of Comcast equipment at the basement of the house or on the street?

 

 

 

2-13-2019, 10:10:55 Critical(3) "Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:0:38 Notice(6) "Honoring MDD; IP provisioning mode = IPv6"
1-1-1970, 0:0:33 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:0:38 Critical(3) "No Ranging Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:0:33 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"
2-11-2019, 22:22:23 Critical(3) "Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:0:33 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:1:52 Critical(3) "No Ranging Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:01:5c:63:36:5a;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:1:49 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"
1-1-1970, 0:0:33 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"
2-11-2019, 22:17:37 Critical(3) "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:01:5c:63:36:5a;CM-QOS=1.1;CM-VER=3.1;"

 

 

Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 699000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
Security Enabled BPI+
DOCSIS Network Access Enabled Allowed  

 

 
Downstream Bonded Channels
Channel ID Lock Status Modulation Frequency Power SNR/MER Corrected Uncorrectables
25 Locked QAM256 699000000 Hz 3.4 dBmV 39.6 dB 0 0
2 Locked QAM256 519000000 Hz 2.6 dBmV 40.4 dB 0 0
3 Locked QAM256 525000000 Hz 2.3 dBmV 40.4 dB 0 0
4 Locked QAM256 531000000 Hz 2.4 dBmV 40.4 dB 0 0
5 Locked QAM256 537000000 Hz 2.7 dBmV 40.4 dB 0 0
6 Locked QAM256 543000000 Hz 2.8 dBmV 40.6 dB 0 0
7 Locked QAM256 549000000 Hz 2.9 dBmV 40.6 dB 0 0
8 Locked QAM256 555000000 Hz 2.7 dBmV 40.3 dB 0 0
9 Locked QAM256 561000000 Hz 2.5 dBmV 40.4 dB 0 0
10 Locked QAM256 567000000 Hz 2.8 dBmV 40.4 dB 0 0
11 Locked QAM256 573000000 Hz 2.7 dBmV 40.3 dB 0 0
12 Locked QAM256 579000000 Hz 2.6 dBmV 40.4 dB 0 0
13 Locked QAM256 585000000 Hz 2.5 dBmV 40.3 dB 0 0
14 Locked QAM256 591000000 Hz 2.4 dBmV 40.3 dB 0 0
15 Locked QAM256 597000000 Hz 2.6 dBmV 40.2 dB 0 0
16 Locked QAM256 603000000 Hz 3.0 dBmV 40.2 dB 0 0
17 Locked QAM256 609000000 Hz 2.6 dBmV 40.0 dB 0 0
18 Locked QAM256 615000000 Hz 2.5 dBmV 39.9 dB 0 0
19 Locked QAM256 621000000 Hz 2.4 dBmV 39.9 dB 0 0
20 Locked QAM256 627000000 Hz 2.2 dBmV 39.7 dB 0 0
21 Locked QAM256 633000000 Hz 2.5 dBmV 39.8 dB 0 0
22 Locked QAM256 639000000 Hz 2.8 dBmV 39.9 dB 0 0
23 Locked QAM256 645000000 Hz 2.6 dBmV 39.8 dB 0 0
24 Locked QAM256 651000000 Hz 2.4 dBmV 39.6 dB 0 0
26 Locked QAM256 657000000 Hz 2.3 dBmV 39.6 dB 0 0
27 Locked QAM256 663000000 Hz 2.5 dBmV 39.8 dB 0 0
28 Locked QAM256 669000000 Hz 3.1 dBmV 40.0 dB 0 0
29 Locked QAM256 675000000 Hz 3.2 dBmV 39.9 dB 0 0
30 Locked QAM256 681000000 Hz 3.0 dBmV 39.7 dB 0 0
31 Locked QAM256 687000000 Hz 3.0 dBmV 39.5 dB 0 0
32 Locked QAM256 693000000 Hz 3.0 dBmV 39.6 dB 0 0
48 Locked Other 850000000 Hz 4.9 dBmV 37.2 dB 0 0

 

 
Upstream Bonded Channels
Channel Channel ID Lock Status US Channel Type Frequency Width Power
1 83 Locked SC-QAM 32300000 Hz 6400000 Hz 43.0 dBmV
2 81 Locked SC-QAM 19300000 Hz 6400000 Hz 43.0 dBmV
3 82 Locked SC-QAM 25700000 Hz 6400000 Hz 43.0 dBmV
4 84 Locked SC-QAM 38700000 Hz 6400000 Hz 43.5 dBmV
Expert

Re: upstream channel power levels too low - what to do.

As stated, the signals are fine but something intermittent may be going on. 

 

Since this is a WiFi connection, for a test, does a computer hardwired directly to the router have the same "outages" ?



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Frequent Visitor

Re: upstream channel power levels too low - what to do.

@EG yes, I did the testing with hardwired computer also, same result. The packet loss is between the modem (192.168.100.1) and the external IP. Really strange.

 

I have spend now about a week looking into eliminating all kinds of possibilities, speaking with Comcast phone support, speaking and emailing with Arris customer support, and it's really difficult. Any suggestions welcome & thanks again for your help.

Expert

Re: upstream channel power levels too low - what to do.


@holunder wrote:

@EG yes, I did the testing with hardwired computer also, same result. The packet loss is between the modem (192.168.100.1) and the external IP. Really strange.

 

FWIW, it's not really "strange", it's fairly common here.

 

The signal stats are o/k but the error log entries indicate that something is going on. Perhaps there is noise ingress into the line(s) somewhere.

 

There are other signal stat figures that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.

 

I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They will be able to poll the CMTS to see whether or not everything is in the green zone, see your node / cable plant and modem health, and also see a history plot for the modem. You should get a reply here in your topic. Good luck !


 



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Official Employee

Re: upstream channel power levels too low - what to do.

Hi, holunder. Thanks for reaching out here for support. If you can please send me private message with your name, I will be more than happy to look into this for you. Like EG stated, I can take a look at the node's health that supplies service to your home, as well as review the signal levels and modem diagnostics from this end. On a purchased modem I will have limitations with manually viewing your additional modem logs, but we can work together on that portion. Please start by sending me a private message with your name and then we can continue publicly afterward if you'd like. 

 

To send a private message, please click my name "ComcastMorgan" then select "Send a Message" on the right side.
 

We will continue digging into this from there. Thank you. 


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Frequent Visitor

Re: upstream channel power levels too low - what to do.

ok, thank you, @EG. I sent a private message to @ComcastMorgan

Expert

Re: upstream channel power levels too low - what to do.

Quite welcome. Good luck with this !



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Official Employee

Re: upstream channel power levels too low - what to do.

Hi again, holunderg. I am glad that the modem swap rectified the issues that you were experiencing. It was great working with you, I appreciate you staying in touch on everything. Take care, have a good one.


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