DOCSIS 3.1 OFDM

[TeDD13]

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?

[Datalink]

@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. 

[TeDD13]

1. Firmware: 2.0.10.36T6

2.

Downstream Overview

Port ID	Frequency (MHz)	Modulation	Signal strength (dBmV)	Channel ID	Signal noise ratio (dB)
1	609000000	256QAM	1.500	10	37.356
2	849000000	256QAM	5.600	2	38.605
3	855000000	256QAM	5.400	3	38.605
4	861000000	256QAM	5.500	4	38.605
5	579000000	256QAM	0.300	5	37.356
6	585000000	256QAM	0.100	6	36.610
7	591000000	256QAM	0.500	7	37.356
8	597000000	256QAM	1.000	8	37.356
9	603000000	256QAM	1.300	9	37.356
10	279000000	256QAM	-4.400	1	37.356
11	615000000	256QAM	1.400	11	37.356
12	621000000	256QAM	1.600	12	37.636
13	633000000	256QAM	2.200	13	37.636
14	639000000	256QAM	2.100	14	37.636
15	645000000	256QAM	2.200	15	37.636
16	651000000	256QAM	2.100	16	37.636
17	657000000	256QAM	2.300	17	37.636
18	663000000	256QAM	2.400	18	37.356
19	669000000	256QAM	3.000	19	38.605
20	675000000	256QAM	2.900	20	38.605
21	681000000	256QAM	2.900	21	37.636
22	687000000	256QAM	2.800	22	37.356
23	693000000	256QAM	2.800	23	37.636
24	699000000	256QAM	3.100	24	37.636
25	705000000	256QAM	3.300	25	38.605
26	711000000	256QAM	3.200	26	38.605
27	717000000	256QAM	3.200	27	37.636
28	723000000	256QAM	3.200	28	37.356
29	825000000	256QAM	4.900	29	38.605
30	831000000	256QAM	5.400	30	38.605
31	837000000	256QAM	5.600	31	38.605
32	843000000	256QAM	5.600	32	38.605

OFDM Downstream Overview

Receiver	FFT type	Subcarr 0 Frequency(MHz)	PLC locked	NCP locked	MDC1 locked	PLC power(dBmv)
0	NA	NA	NO	NO	NO	NA
1	4K	275600000	YES	YES	YES	-3.099998

Upstream Overview

Port ID	Frequency (MHz)	Modulation	Signal strength (dBmV)	Channel ID	Bandwidth
1	22100000	ATDMA - 64QAM	45.750	1	3200000
2	36996000	ATDMA - 64QAM	43.750	4	6400000
3	30596000	ATDMA - 64QAM	42.500	3	6400000
4	25300000	ATDMA - 64QAM	45.750	2	3200000

OFDM/OFDMA Overview

Channel Index	State	lin Digital Att	Digital Att	BW (sc's*fft)	Report Power	Report Power1_6	FFT Size
0	DISABLED	0.5000	0.0000	0.0000	-inf	-1.0000	4K
1	DISABLED	0.5000	0.0000	0.0000	-inf	-1.0000	4K

[Datalink]

@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?"