Intermittent T3 Timeouts

[DeadSignal]

Hi all,

TL;DR - Shibboleet help please! Am I being a muppet or is this upstream?

For background - I'm a Linux analyst and CCNA qualified but know very little about DOCSIS.

I'm getting occasional T3 (and previous T4) dropouts plus a bunch of Post-RS errors. I understand this is bad! 🤔

VM Superhub 3.0
Hardware version : 11
Software version : 9.1.2109.200
Last reboot: 06/02/2023 ~18:40

My first concern is that the superhub was delivered without a coax cable so currently have no primary isolator (I have the PSU into the VM wall-box setup... I'd love to know how this works!)

I'm currently using about 5m of CT100 cable, kept from last year's VM subscription.

Secondly, I noted a kernel panic in the logs when I first booted it! This has since disappeared.

Here's the log. 23:43 was when my Twitch broadcast dropped for a few seconds:

Time Priority Description

11/02/2023 01:25:37	notice	LAN login Success;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
10/02/2023 23:43:22	Warning!	Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
10/02/2023 23:43:17	critical	SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
10/02/2023 23:43:16	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
10/02/2023 23:43:16	critical	SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
10/02/2023 13:11:38	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
09/02/2023 15:49:5	Error	DHCP RENEW WARNING - Field invalid in response v4 option;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
06/02/2023 18:43:51	notice	LAN login Success;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

Up/Down metrics in comments due to character limit.

TIA. Rich.

[DeadSignal]

Here's the Metrics:

Downstream:

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

1	426250000	5	34	256 qam	9
2	362250000	4	34	256 qam	1
3	370250000	4.4	34	256 qam	2
4	378250000	4.5	34	256 qam	3
5	386250000	4.5	34	256 qam	4
6	394250000	4.9	34	256 qam	5
7	402250000	5	34	256 qam	6
8	410250000	5	34	256 qam	7
9	418250000	5	34	256 qam	8
10	434250000	5	34	256 qam	10
11	442250000	5.3	34	256 qam	11
12	450250000	5.1	34	256 qam	12
13	458250000	4.9	34	256 qam	13
14	466250000	5	34	256 qam	14
15	474250000	4.8	34	256 qam	15
16	482250000	4.6	34	256 qam	16
17	490250000	4.5	34	256 qam	17
18	498250000	4.4	34	256 qam	18
19	506250000	4.3	34	256 qam	19
20	514250000	4.1	34	256 qam	20
21	522250000	4	34	256 qam	21
22	530250000	3.9	34	256 qam	22
23	538250000	4	34	256 qam	23
24	546250000	3.9	34	256 qam	24

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

1	Locked	34.4	154939	6519
2	Locked	34.4	182167	6062
3	Locked	34.3	346294	6061
4	Locked	34.3	280815	5980
5	Locked	34.4	284593	6431
6	Locked	34.9	179684	6656
7	Locked	34.4	166645	6647
8	Locked	34.4	263489	6408
9	Locked	34.4	158990	6862
10	Locked	34.9	107150	6441
11	Locked	34.9	98195	6398
12	Locked	34.4	201984	6314
13	Locked	34.3	193419	6179
14	Locked	34.4	135915	6478
15	Locked	34.9	150725	6554
16	Locked	34.9	155710	6611
17	Locked	34.4	246839	6512
18	Locked	34.3	141611	6566
19	Locked	34.3	185919	6557
20	Locked	34.4	226785	6648
21	Locked	34.4	341202	6559
22	Locked	34.3	290900	6489
23	Locked	34.4	189801	6580
24	Locked	34.4	116016	6531

Upstream:

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

1	46200000	36	5120	64 qam	3
2	39399965	36	5120	64 qam	4
3	60299951	35.8	5120	64 qam	1
4	53699971	36	5120	64 qam	2

Channel Channel Type T1 Timeouts T2 Timeouts T3 Timeouts T4 Timeouts

1	ATDMA	0	0	0	0
2	ATDMA	0	0	0	0
3	ATDMA	0	0	1	0
4	ATDMA	0	0	0	0

[Andrew-G]

Possibly the cable you're using is not adequate for cable internet, which is hugely vulnerable to radio interference if the wrong cables are used.  VM normally use their own triple shielded  RG6 for that reason.  I'd suggest you're looking at booking a £25 non-fault call out to have the connection looked at, the hub connected with the right cable, and SNR checked.

[DeadSignal]

Thanks for the info.

Do you have the specs for this cable?

Standard RG6 is single aluminium shielded. That's why I've always used CT100. Same impedance, same attenuation but duofoil shielded and harder to kink.

[DeadSignal]

Quick update. 

I've put it on a 0.5m cable cut from a fresh reel and I'll contact support on Monday to get a VM supplied one.

[Client62]

If the PSU into the VM wall box is like this, it is an RFoG / FTTP area.

The PSU via the coax is powering an ONU in the external OMNI box. 

[DeadSignal]

Nice one. Thank you @Client62.

That's my exact setup. 

I guessed it was FTTP

I assume the external piece of kit is effectively an ER fibre to RF modem.

Seems kinda mad that it isn't simply converted to copper ethernet.

Thanks for the details. I'm going to have some fun on Google this afternoon 😁

[Client62]

I agree with the comments about coax cable quality being suspect for the following reasons ...

We are an RFoG area with a 10dB attenuator on the Hub3's coax - our Downstream Power levels are about 8 dB below those shown above.

But our Hub3's Downstream SNR figures are higher (read better) , and the number of Pre RS & Post RS errors are minimal.

If the Post RS (Reed-Solomon) i.e. the uncorrectable errors can be sorted a smoother connection should be possible.

PS ... for primary isolation, the 50+ meters of fibre cable will see to that.

[Client62]

Reading materials

https://www.commscope.com/globalassets/digizuite/1641-arris-hfctofttp-whitepaper-final.pdf 

https://www.profiber.eu/files/produkty/aktivne_prvky/HFC_Hlavne_stanice_opticke_node/BOOSTRAL_711/16...

[DeadSignal]

I think you may both be bang on about the cable.

4h after swapping to a short cable - Zero Post RS errors and zero warnings.

I'll keep an eye on it for a couple of days and do some reading so that I can understand the power and SNR thresholds.

To be fair, I should have just run a longer ethernet cable in the first place, I was just being lazy 😁

Thank you very much for the docs and technical info.