DSL diagnosis

digiman · 01-12-2017 9:50pm #1

I need help with my parents broadband connection here. They are using Vodafone with a Huawei 658c over OpenEir copper line, they are about 4km exchange and their stats are as follows:

Connection Status
DSL synchronization status Up
DSL up time 00:00:29

Line Status
Line standard G.dmt
Downstream line rate (kbit/s) 7232
Upstream line rate (kbit/s) 512
Downstream SNR (dB) 6.1
Upstream SNR (dB) 24
Downstream line attenuation (dB) 32.5
Upstream line attenuation (dB) 15
Downstream output power (dBmV) 19.9
Upstream output power (dBmV) 12.1
Downstream CRC 320427
Upstream CRC 0
Downstream FEC 36397966
Upstream FEC 0

I've a constant ping going to www.rte.ie and the results are as below:

--- www.rte.ie ping statistics ---
1106 packets transmitted, 914 packets received, 17.4% packet loss
round-trip min/avg/max/stddev = 30.161/1505.009/76615.174/7191.691 ms

I've also ran a ping to 192.168.1.1 and it's perfect so looks like a WAN side issue.

--- 192.168.1.1 ping statistics ---
1661 packets transmitted, 1661 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 1.372/2.665/103.319/4.582 ms

If it was an FTTH line I would know exactly what was wrong but I'm not familiar with DSL at all really.

When it is steady for a few minutes, it will have a ping of around 32ms but then will timeout for a minute or so, when I do a speedtest it will get around 6Mb/s down and 0.5Mb/s up. Some pings results can then jump up to 300 or 400ms for a while and then fall again to 32ms again or could even jump back up again to seconds at times or just even time out for a couple of minutes.

Any thoughts, I will give Vodafone a call in the morning and I have a Huawei 659 I can swap it out for shortly as well but I don't suspect a modem fault. I just want to be as informed as I can be before calling Vodafone as they will probably just try to swap the modem or they will wait a few days for an OpenEir engineer to call and I won't be here then to quiz him about it.

shigllgetcha · 01-12-2017 11:24pm

Downstream snr is too low. I had 6 for a while and it cut out constantly.

The speed at 4km is too high call Vodafone and have it reduced. Im at 3.5km and can only have 5mbps, theirs is set to 7mbps.

There are times a fault will cause noise on the line, low snr, but theirs seems like its set far too high and that can cause lowe snr and cut outs

ED E · 02-12-2017 2:13am

Something doesnt match up here. Probably where you think the exchange is vs where it is.

Loop length above is 2600m, and they've profiled you for 8Mb OR MORE. That indicates more like a 10-12Mb line thats underperforming.

Without more info either the 658c is being **** (its the cheapest possible unit) and you are on a longer loop, or you're on a shorter loop that needs troubleshooting.

Basic questions apply:
Is the modem at MDP
Alarm?
Medi Alert
Phone handsets

Putting the line to 6Mb might get you stability/less instability, but I suspect you can do a lot better.

digiman · 02-12-2017 9:57am

ED E wrote: »

Something doesnt match up here. Probably where you think the exchange is vs where it is.

Loop length above is 2600m, and they've profiled you for 8Mb OR MORE. That indicates more like a 10-12Mb line thats underperforming.

Without more info either the 658c is being **** (its the cheapest possible unit) and you are on a longer loop, or you're on a shorter loop that needs troubleshooting.

Basic questions apply:
Is the modem at MDP
Alarm?
Medi Alert
Phone handsets

Putting the line to 6Mb might get you stability/less instability, but I suspect you can do a lot better.

How do you calculate the loop length from the stats?

What is the MDP?
A house alarm was installed in the last year, I assume medi alert is some type of medical alert, if so they don’t have.
There is a fax machine and also one portable handset in the house.

I’ve checked again and the distance to the exchange is 4.1km along the road. It is pretty rural so not many exchanges it can be. Could Vodafone verify this when I talk to them on their support?

Is the best thing now to try the 659 and disconnect everything else and see what the SNR looks like with just the broadband connected?

digiman · 02-12-2017 11:19am

Just to add here is my line stats for this morning, no changes made to anything yet.

Line standard G.dmt
Downstream line rate (kbit/s) 7040
Upstream line rate (kbit/s) 512
Downstream SNR (dB) 8.1
Upstream SNR (dB) 23
Downstream line attenuation (dB) 32.5
Upstream line attenuation (dB) 15
Downstream output power (dBmV) 20
Upstream output power (dBmV) 11.8
Downstream CRC 335190
Upstream CRC 0
Downstream FEC 36482657
Upstream FEC 0

What would have increased the SNR by so much since last night?

Also, is the line being adaptive in that the Downstream rate has also slightly changed?

digiman · 02-12-2017 1:00pm

So I've just swapped out the 658c for a 659 and the results are as below:

DSL synchronization status:
Up
Connection status:
Showtime
Upstream line rate (kbit/s):
512
Downstream line rate (kbit/s):
7712
Maximum upstream rate (kbit/s):
1276
Maximum downstream rate (kbit/s):
8464
Upstream noise safety coefficient (dB):
23
Downstream noise safety coefficient (dB):
6.1
Upstream interleave depth:
64
Downstream interleave depth:
2
Line standard:
ADSL_G.dmt
Upstream line attenuation (dB):
15
Downstream line attenuation (dB):
32.5
Upstream output power (dBmV):
12.1
Downstream output power (dBmV):
19.9
Channel type:
Interleaved
Erroneous seconds:
0 days 0 hours 0 minutes 0 seconds
DSL up time:
0 days 0 hours 5 minutes 41 seconds

Interesting that the downstream line attenuation is staying the same but the SNR is now back again to what it was last night. I'll leave this for an hour or so and check the ping results when I get back.

ED E · 02-12-2017 1:04pm

It dropped and re synchronized at a slightly lower rate. Probably not enough alone to account for the 2dB but partly. The SNRM changes from second to second but the modem only displays the last sync normally so its only a snapshot view.

The must have a bundle to themselves to get very minimal attenuation like that.

MDP = Main socket (hallway normally)

What you should do is disconnect the alarm(if you're handy with a screwdriver, itll beep at you for it) phone and fax. Then reboot the modem and check the stats.

shigllgetcha · 02-12-2017 4:11pm

When i had problems my snr went up when youd expect less people to using the internet and fall when more people were online, evenings etc and cut out far more.

digiman · 02-12-2017 4:30pm

shigllgetcha wrote: »

When i had problems my snr went up when youd expect less people to using the internet and fall when more people were online, evenings etc and cut out far more.

So I called into them there now and they dropped the profile from 8 to 7 and then I asked them to drop it to 4 and the SNR has now gone to 19.3 so will monitor it at that for a while and see how it goes for a while.

shigllgetcha · 03-12-2017 11:15pm

19.3 might be overkill, mine is good at 12 but i guess itll be really stable at that

ED E · 04-12-2017 1:42am

dB is a logarithmic scale. 9dB is 2x 6dB. Once you hit 8 with ADSL you should be in safe territory.

digiman · 05-12-2017 9:48pm

ED E wrote: »

dB is a logarithmic scale. 9dB is 2x 6dB. Once you hit 8 with ADSL you should be in safe territory.

Thanks for that, doesn't look like it's anything with the SNR then so as even at 19dB it is still dropping packets and huge variations with the latency.

ED E · 05-12-2017 10:36pm

Then we can deduce the source of the issue is variable.

If you get a tech out with a meter he'll be able to diagnose it properly.

DSL diagnosis

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