DOCSIS 3.1 and 4096 QAM attenuation - technical question

[ST4]

I have recently had a problem. 

I upgraded my M500 to 1GB and am not getting any think like the speeds that I should and am just getting over 535mb

Strangely my upload speeds are 50 to 52mb so in the right provisioning band for 1GB product and they if I am correct in my thinking on DOCSIS 3.0 (and the D/L on 3.1) 

I have had two engineer visits and still no further on, equipment and FTTP are okay

I am using a HUB4 which has been changed, but no change in speeds.

The provisioning appears to be correct and the levels are ok

My question is this, has anyone got a HUB4 with a wideband -3db attenuator that is getting 1GB+ 

On rebooting my Hub4  the QAM starts at 4096 and within 20 minutes drops to 2048, my speeds never seem to go above 550mb(measured direct at the HUB with 1GB nic and cat6 cable. (this happens with or without the attenuator in place)

I have ruled out everything else and am coming to the conclusion that it might be something with the attenuator or a miss match from the cabinet. 

Unfortunately there is no one else on my cabinet on 1GB so can't even find out if it is a local issue which is starting to get frustrating

Any help or idea appreciated

[ST4]

3.1 Downstream channels

Channel Channel Width (MHz) FFT Type Number of Active Subcarriers Modulation (Active Profile) First Active Subcarrier (Hz)

159

96

4K

1880

QAM2048

424

error occurring after 12 mins

DBC-REQ Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=ac:f8:xx:xx:xx:xx;CMTS-MAC=00:eb:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;

[gitty]

The change of modulation profile is a way to protect you from data loss. If the loss only happens on the highest profile, you are protected from it. By itself, it cannot explain why you cannot go above ~500 Mbps.

[ST4]

All the levels and stats look fine, the line has been tested, the router changed the only thing I can think of is that there is an incorrect provision somewhere on the network as the router has been changed and is showing the correct provision

Refresh data

Cable Modem StatusItem Status CommentsChannel Overview Downstream Upstream

Cable Modem Status	Online	DOCSIS 3.1
Primary downstream channel	Locked	SC-QAM
DOCSIS 3.0 channels	31	4
DOCSIS 3.1 channels	1	0

Refresh data

3.0 Downstream channels

Channel Frequency (Hz) Power (dBmV) SNR (dB) Modulation Channel ID

25	331000000	1.2	39	QAM256	25
1	139000000	2.7	39	QAM256	1
2	147000000	2.6	39	QAM256	2
3	155000000	2.7	39	QAM256	3
4	163000000	2.7	39	QAM256	4
5	171000000	2.8	39	QAM256	5
6	179000000	2.9	39	QAM256	6
7	187000000	2.9	39	QAM256	7
8	195000000	3	39	QAM256	8
9	203000000	3	39	QAM256	9
10	211000000	2.9	40.4	QAM256	10
11	219000000	2.9	40.9	QAM256	11
12	227000000	2.9	40.4	QAM256	12
13	235000000	2.8	39	QAM256	13
14	243000000	2.9	40.9	QAM256	14
15	251000000	2.7	39	QAM256	15
16	259000000	2.7	40.4	QAM256	16
17	267000000	2.2	40.4	QAM256	17
18	275000000	2	40.4	QAM256	18
19	283000000	2	40.4	QAM256	19
20	291000000	2.3	40.4	QAM256	20
21	299000000	2.6	40.4	QAM256	21
22	307000000	2.1	40.4	QAM256	22
23	315000000	1.8	40.4	QAM256	23
24	323000000	1.3	39	QAM256	24
26	339000000	1.5	40.4	QAM256	26
27	347000000	1.6	39	QAM256	27
28	355000000	1.3	40.4	QAM256	28
29	363000000	1.3	39	QAM256	29
30	371000000	1.5	40.4	QAM256	30
31	379000000	1.4	39	QAM256	31

[ST4]

3.0 Downstream channels

Channel Lock Status RxMER (dB) Pre RS Errors Post RS Errors

25	Locked	38.983261	0	0
1	Locked	38.983261	0	0
2	Locked	38.983261	0	0
3	Locked	38.983261	0	0
4	Locked	38.983261	0	0
5	Locked	38.983261	0	0
6	Locked	38.983261	0	0
7	Locked	38.983261	0	0
8	Locked	38.983261	0	0
9	Locked	38.983261	0	0
10	Locked	40.366287	0	0
11	Locked	40.946209	0	0
12	Locked	40.366287	0	0
13	Locked	38.983261	0	0
14	Locked	40.946209	0	0
15	Locked	38.983261	0	0
16	Locked	40.366287	0	0
17	Locked	40.366287	0	0
18	Locked	40.366287	0	0
19	Locked	40.366287	0	0
20	Locked	40.366287	0	0
21	Locked	40.366287	0	0
22	Locked	40.366287	0	0
23	Locked	40.366287	0	0
24	Locked	38.983261	0	0
26	Locked	40.366287	0	0
27	Locked	38.983261	0	0
28	Locked	40.366287	0	0
29	Locked	38.983261	0	0
30	Locked	40.366287	0	0
31	Locked	38.983261	0	0

3.1 Downstream channels

Channel Channel Width (MHz) FFT Type Number of Active Subcarriers Modulation (Active Profile) First Active Subcarrier (Hz)

159

96

4K

1880

QAM2048

424

3.1 Downstream channels

Channel ID Lock Status RxMER Data (dB) PLC Power (dBmV) Correcteds (Active Profile) Uncorrectables (Active Profile)

159

Locked

43

2.5

498358109

0

[ST4]

Refresh data

3.0 Upstream channels

Channel Frequency (Hz) Power (dBmV) Symbol Rate (ksps) Modulation Channel ID

1	60300000	36	5120 KSym/sec	64QAM	1
2	39400000	35.3	5120 KSym/sec	64QAM	4
3	46200000	35.3	5120 KSym/sec	64QAM	3
4	53700000	36	5120 KSym/sec	64QAM	2

3.0 Upstream channels

Channel Channel Type T1 Timeouts T2 Timeouts T3 Timeouts T4 Timeouts

1	US_TYPE_STDMA	0	0	0	0
2	US_TYPE_STDMA	0	0	0	0
3	US_TYPE_STDMA	0	0	1	0
4	US_TYPE_STDMA	0	0	1	0

[ST4]

Refresh data

General Configuration

Network access	true
Maximum Number of CPEs	1
Baseline Privacy	true
DOCSIS Mode	3.1
Config file	87dsfd;kfoA,.iyewrkldJKDHSUBs

Primary Downstream Service Flow

SFID	28819
Max Traffic Rate	1200000450
Max Traffic Burst	42600
Min Traffic Rate	0

Primary Upstream Service Flow

SFID	29465
Max Traffic Rate	55000270
Max Traffic Burst	42600
Min Traffic Rate	0
Max Concatenated Burst	16320
Scheduling Type	bestEffort

[ST4]

error log (same event every reboot)

Fri 04/03/2022 17:32:41	5	MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=ac:f8:xx:xx:xx:xx;CMTS-MAC=00:eb:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Fri 04/03/2022 17:44:57	5	DBC-REQ Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=ac:f8:xx:xx:xx:xx;CMTS-MAC=00:eb:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;

MAC ac:f8:xx:xx:xx:xx  ARRIS Router (HUB4)

MAC 00:eb:**:**:**:** CISCO (Cabinet)

[Hayley_S]

Hello @ST4,

Welcome back, thanks for posting.

I am sorry for any issues with your broadband.

I have checked our system, I am not able to see any known issues causing any problems.

How is your service for you today?

Many thanks,

[ST4]

No further on, I have applied to cancel my line

Thanks

[Tom_W1]

Hi @ST4, thanks for your reply and I'm very sorry to hear that.

We have exhausted all of our checks at the moment and there is no reason you should still be getting just 500mbps or under. I'll leave this thread open in case you need our support until you disconnect, or we can provide any further support.

Sincere apologies.

Many thanks