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XDGFX
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Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Hi all,

I've seen similar posts to this one before, but they all either end without resolution, or after a VM member starts a private chat with the OP.

I get intermittent slow speeds on my VM 350 connection. Some days this will happen every 5-10 minutes, dropping the speed down to ~0.5Mbps, before returning back to ~full speed. Some days are without issue.

This happens on wired connections as well as WiFi.

I'm using Modem Mode, the router is an EdgeRouter X. Speedtests on the ER also show the same slowdown, so I'm fairly confident it's the VM hub.

As suggested in other threads I've set up a Broadband Quality Monitor here. So far it shows nothing too unexpected.

I have been getting critical errors in the VM hub network log (note MAC addresses have been redacted):

Time	Priority	Description
05/07/2021 16:58:16	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 16:46:17	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 10:49:29	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 08:32:43	critical	SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 08:23:39	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 08:04:22	notice	LAN login Success;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
05/07/2021 08:04:14	Warning!	LAN login FAILED : Incorrect Username / Password / ConnectionType;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
04/07/2021 12:27:28	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
04/07/2021 10:46:6	critical	SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:51:40	Warning!	RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:37:55	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:37:31	critical	Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:37:31	critical	Ranging Request Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:31:6	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:30:42	critical	Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:30:42	critical	Ranging Request Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:24:18	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:23:54	critical	Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:23:54	critical	Ranging Request Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
03/07/2021 10:17:29	critical	No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

 

Most notably No Ranging Response received and SYNC Timing Synchronization failure

Upstream and downstream bonded channels are shown below, I'm not sure if these indicate an issue but each channel looks relatively consistent at least.

 

Downstream bonded channels
Channel	Frequency (Hz)	Power (dBmV)	SNR (dB)	Modulation	Channel ID
1	474250000	8	38	256 qam	9
2	410250000	9.6	38	256 qam	1
3	418250000	9.3	38	256 qam	2
4	426250000	8.9	40	256 qam	3
5	434250000	8.5	38	256 qam	4
6	442250000	8.3	40	256 qam	5
7	450250000	8	38	256 qam	6
8	458250000	7.9	38	256 qam	7
9	466250000	7.9	38	256 qam	8
10	482250000	8.1	38	256 qam	10
11	490250000	8	38	256 qam	11
12	498250000	7.8	38	256 qam	12
13	506250000	7.5	38	256 qam	13
14	514250000	7.5	38	256 qam	14
15	522250000	7.8	38	256 qam	15
16	530250000	7.5	38	256 qam	16
17	538250000	7	38	256 qam	17
18	546250000	6.6	38	256 qam	18
19	554250000	6.6	38	256 qam	19
20	562250000	6.8	38	256 qam	20
21	570250000	7	38	256 qam	21
22	578250000	6.6	38	256 qam	22
23	586250000	6.4	38	256 qam	23
24	594250000	6.5	38	256 qam	24


Downstream bonded channels
Channel	Locked Status	RxMER (dB)	Pre RS Errors	Post RS Errors
1	Locked	38.9	771	789
2	Locked	38.9	2346	452
3	Locked	39.3	2215	469
4	Locked	40.3	2000	522
5	Locked	38.9	2040	703
6	Locked	40.3	1805	712
7	Locked	38.9	1656	798
8	Locked	38.9	1338	875
9	Locked	38.9	991	1035
10	Locked	38.9	587	586
11	Locked	38.9	543	485
12	Locked	38.9	483	601
13	Locked	38.9	337	348
14	Locked	38.9	286	143
15	Locked	38.9	295	27
16	Locked	38.6	256	6
17	Locked	38.6	307	0
18	Locked	38.9	444	4
19	Locked	38.6	508	20
20	Locked	38.9	558	30
21	Locked	38.9	553	15
22	Locked	38.9	511	52
23	Locked	38.9	494	42
24	Locked	38.6	465	33


Upstream bonded channels
Channel	Frequency (Hz)	Power (dBmV)	Symbol Rate (ksps)	Modulation	Channel ID
1	39400000	39.2	5120	16 qam	2
2	25800024	32.5	5120	16 qam	4
3	32600380	33.2	5120	16 qam	3
4	46200000	35	5120	16 qam	1


Upstream bonded channels
Channel	Channel Type	T1 Timeouts	T2 Timeouts	T3 Timeouts	T4 Timeouts
1	ATDMA	0	0	0	0
2	ATDMA	0	0	2	0
3	ATDMA	0	0	0	0
4	ATDMA	0	0	0	0

 

Any suggestions on fixing this issue?

My Broadband Ping - VM Quality
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lotharmat
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Hiya,

Usually the private chat is a VM forum rep confirming identity and then booking an engineer - which you will need! 😉

Your upstream is out of spec which will need to be put right by said engineer!

Hang tight for forum staff!



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Hub 3 - Modem Mode - TP-Link Archer C7

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XDGFX
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Hey!

Gotcha. What signifies it's out of spec? Could you please point me towards what it should look like or some information for me to learn more about what it means?

Thanks

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lotharmat
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Helpful Answer

Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Basically - Downstream should be between -6 and +10dBmV with an SNR above 34 and RxMER similar!

Upstream power should be between 34 and 51 dBmV at 64 QAM

There is a really good 'sticky' post that goes into all the technical side of it - but this is generally what VM looks for! - If your network log or BQM (see my signature) looks horrendous and all the levels look OK - they will usually still book an engineer as there is clearly a problem!
This is why it is good practice to keep a BQM going!



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Hub 3 - Modem Mode - TP-Link Archer C7

lotharmat
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Here you go:

https://community.virginmedia.com/t5/QuickStart-set-up-and/POWER-LEVELS-amp-SNR-A-TECHNICAL-PRIMER-u...



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Hub 3 - Modem Mode - TP-Link Archer C7

XDGFX
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Ah perfect, thanks a lot. I'll see if I can contact them by phone tomorrow and I'll update here if I get the issue resolved.

My Broadband Ping - VM Quality
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lotharmat
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Definitely keep us posted!



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Hub 3 - Modem Mode - TP-Link Archer C7

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XDGFX
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Gave them a call, apparently there's a local issue currently due to performance improvements in my area. I doubt this is affecting the issue as I've had it for months, but they said no tests could be performed reliably while this work is taking place.

I'll try again on the 9th when it should be completed, if a rep doesn't appear here sooner.

My Broadband Ping - VM Quality
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Zoie_P
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Hi XDGFX,

Thanks for your post 🙂
I have managed to locate your account.

Yes, there is an outage in your area, this is a congestion outage and it can last a while.

If you are still having issues after the estimated fix date please let us know and we can help

Zoie

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XDGFX
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Re: Intermittent slow speeds (~0.5Mbps) for 30s, Modem Mode, Normally 300Mbps+

Hi Zoie,

Still having issues I'm afraid. The reboot seemed to help temporarily, though I restarted yesterday after the issue happened around 10am and problems persist today.

Running a traceroute on the Ubiquity Edgerouter (connected right to the VM router in modem mode) shows dropped packets in the same pattern as running it on my desktop connected to the ER, so I don't believe the ER is contributing to the issue.

Screenshot from 2021-08-06 11-07-27.jpg

Looking at the VM logs there are the same errors I've mentioned previously, but these have appeared intermittently over the last few days. The issue is present now and there are no error logs at this time.

Not too sure where to go from here, any help is appreciated!

 

Note: Ignore the big block of red in my BQM - I'd accidentally removed the ICMP response firewall rule 😉

My Broadband Ping - VM Quality
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