DOCSIS 3.1 OFDM

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I'm a Trusted Contributor
Posts: 339

DOCSIS 3.1 OFDM

I am on 300/20 plan and was getting advertised speeds consistently until about 5 days ago, when my download speeds went from about 280 to 94 and still do not exceed 94. Here is what happened 5 days ago:

 

- ROGERS and BELL trucks spent two days on a street near my home.

- about 2 days ago download LED indicator on my CODA-4582 went from solid blue to solid cyan. 

 

As I never saw solid cyan light before on my modem I went to see in the gateway manual what it was. HITRON manual says that solid cyan means "DOCSIS 3.1 OFDM". I went into my modem DOCSIS status page and saw 1 available OFDM channel in one section and "OFDM disabled" in another one.

 

Can someone tell me what is going on and if there is anything to worry about?

 

 

Resident Expert
Resident Expert
Posts: 6,154

Re: DOCSIS 3.1 OFDM

@TeDD13 OFDM DOCSIS 3.1 is normal ops for the CODA-4582.  Running a single OFDM channel is the current configuration for the CMTS and modem.  Your current download speeds are not normal.  With that in mind, can you log into the modem and:

 

1.  Confirm what Sofware Version (firmware) is currently loaded, as indicated on the STATUS tab that is displayed when you log into the modem;

 

2.  Navigate to the DOCSIS WAN tab and copy the Downstream Overview, all the way down to the bottom of the OFDM/OFDMA section.  Select or highlight that entire table, right click ..... Copy.  Then paste that into a new post, right click ..... Paste.  That will paste the table into a post.  

 

With the signal levels available, the cause of the slow data rates might be evident. 



I'm a Trusted Contributor
Posts: 339

Re: DOCSIS 3.1 OFDM

1. Firmware: 2.0.10.36T6

2.

Downstream Overview
Port IDFrequency (MHz)ModulationSignal strength (dBmV)Channel IDSignal noise ratio (dB)
1609000000256QAM1.5001037.356
2849000000256QAM5.600238.605
3855000000256QAM5.400338.605
4861000000256QAM5.500438.605
5579000000256QAM0.300537.356
6585000000256QAM0.100636.610
7591000000256QAM0.500737.356
8597000000256QAM1.000837.356
9603000000256QAM1.300937.356
10279000000256QAM-4.400137.356
11615000000256QAM1.4001137.356
12621000000256QAM1.6001237.636
13633000000256QAM2.2001337.636
14639000000256QAM2.1001437.636
15645000000256QAM2.2001537.636
16651000000256QAM2.1001637.636
17657000000256QAM2.3001737.636
18663000000256QAM2.4001837.356
19669000000256QAM3.0001938.605
20675000000256QAM2.9002038.605
21681000000256QAM2.9002137.636
22687000000256QAM2.8002237.356
23693000000256QAM2.8002337.636
24699000000256QAM3.1002437.636
25705000000256QAM3.3002538.605
26711000000256QAM3.2002638.605
27717000000256QAM3.2002737.636
28723000000256QAM3.2002837.356
29825000000256QAM4.9002938.605
30831000000256QAM5.4003038.605
31837000000256QAM5.6003138.605
32843000000256QAM5.6003238.605
OFDM Downstream Overview
ReceiverFFT typeSubcarr 0 Frequency(MHz)PLC lockedNCP lockedMDC1 lockedPLC power(dBmv)
0NANANONONONA
14K275600000YESYESYES-3.099998
Upstream Overview
Port IDFrequency (MHz)ModulationSignal strength (dBmV)Channel IDBandwidth
122100000ATDMA - 64QAM45.75013200000
236996000ATDMA - 64QAM43.75046400000
330596000ATDMA - 64QAM42.50036400000
425300000ATDMA - 64QAM45.75023200000
OFDM/OFDMA Overview
Channel IndexStatelin Digital AttDigital AttBW (sc's*fft)Report PowerReport Power1_6FFT Size
0DISABLED0.50000.00000.0000-inf-1.00004K
1DISABLED0.50000.00000.0000-inf-1.00004K

 

Resident Expert
Resident Expert
Posts: 6,154

Re: DOCSIS 3.1 OFDM

@TeDD13 Your DOCSIS 3.0 channels (1 to 32) don't look too bad.  Port 10 is worth noting as its below 0 dBmV.  For DOCSIS 3.0 its livable, but, its odd compared to the other channels.  That channel happens to be just above the first sub-carrier of the DOCSIS 3.1 OFDM channel.  There isn't enough data to determine the health of the OFDM channel but, there is most definitely a signal ramp up from 275.6 Mhz upwards to the end point of the OFDM channel which will be at 467.6 Mhz.  How that ramp up will affect the channel performance is anyone's guess.  

 

The DOCSIS 3.0 upstream levels are within spec, but, that modem typically runs in the neighbourhood of 30 to 32 dBmV for the upstream transmit power.  so, your modem is running about 10 to 15 dB higher than normal.  

 

Personal opinion, there's some issue within the lower 500 Mhz region on your cable.  The signal levels aren't where they normally are, although yes, arguably their within spec.  Your download speeds are also way off of where they should be.  

 

Call tech support and ask the Customer Service Rep to run a signal check on your modem.  See if it passes.  Based on the DOCSIS 3.0 numbers it probably would.  The unknown factor here is the DOCSIS 3.1 data.  Ask the CSR what the OFDM signal to noise ratio number happens to be and what the QAM number is.  In a normal environment, that QAM number should be 1024.  It will drop if there are problems in that channel, with 64 QAM being the lowest supportable level.  Below that, the modem will bail out of the OFDM channel and switch to the DOCSIS 3.0 channels.  I'll be interested in that QAM number, just to see where you're at. 

 

Note that it might take the CSR a minute or two to find the OFDM numbers.  Their either at the bottom of the page that shows the modem's data, out of view, or on the next page.  You might surprise the CSR when you ask for those numbers.  The follow on question is, "are the numbers within spec?"