Please may I have an explanation of how the SNR affects broadband delivery?

[#1]

Quote from: Anotherone

So, are you able to borrow another modem/router (or do you have a spare) that you can use for 24-48 hours or so?

For many years, my setup was a D-Link DSL-502T router connected to a Buffalo Air Station G54 router. This setup worked well except there were some websites which I could not access... not really sure why and since I didn't find it restrictive, I did not try to identify the problem... this setup certainly ensured that several PCs on a home network easily kept connected...
I was reluctant to change over the 585v8 sent to me by Plusnet because the first thing I noticed was an inability to keep all PCs on the network connected... it is a bit better now because I have an additional hub which appears to help keep PCs connected...
Another reason why I am now using the Thomson 585v8 is because it makes it easy for other family members to connect their iPads and iPhones, etc...
I'm sure I'll be able to revert to the D-Link...
Today, the SNR has been stable at between 5 and 6 all day...

[#2]

Before you do that, I need to check how easy it will be to monitor the ADSL connection with it, otherwise it may be best to organise something else.

[#3]

This is what my ADSL stats were with auto mode which ended up on ADSL2+
[tt]US Connection Rate:    752    DS Connection Rate:    3415
DS Line Attenuation:    60.5    DS Margin:              6.2
US Line Attenuation:    36.9    US Margin:              5.0[/tt]
(and often the DS rate was closer to 3200)
These are my current ADSL stats now that I set ADSL2 mode
[tt]US Connection Rate:    882    DS Connection Rate:    3818
DS Line Attenuation:    58.3    DS Margin:              6.0
US Line Attenuation:    36.6    US Margin:              5.0[/tt]
If your exchange (or the combination of your exchange and your modem/router) doesn't automatically end up on ADSL2 (G.992.3) on a long line, and instead runs them on ADSL2+ (G.992.5), then selecting ADSL2 may well be a better setting.
Looks like the D-Link DSL-502T is based on the AR7 chipset and works with RouterStats.

[#4]

ejs, whilst changing mode may have improved your connection, there is already two major issues here (at least) affecting this connection. Introducing another variable into the situation at this time is extremely unwise especially when it's effects may be completely masked by the other issues as I've already said.in reply #59, so continuing to mention it is only detracting from the other issues.
Thanks for the info about the DSL-502T, however, there are two different models - Gen I and Gen II.  Gen I is apparently a horizontal Grey unit, whereas Gen II is Blue & Silver and can be vertical. I haven't found out if they have the same chipsets.
@Richard, can you tell us which model DSL-502T it is that you've got?

[#5]

Both AR7
http://wiki.openwrt.org/oldwiki/openwrtdocs/hardware/d_link/dsl_502t
http://wiki.openwrt.org/toh/d-link/dsl-502t-genii
Yes and one of the issues is that's it's running in suboptimal ADSL2+ mode.

[#6]

Thank you Anotherone and ejs... for your thoughts...
The RouterStats are more impressive today leading me to wonder whether the traffic at the exchange is less on a Sunday morning... 
Whilst I have been preparing the appended images, the stats for my broadband service have taken a dive... leading me to believe that all my problems are really at the local exchange... perhaps ejs's solution is the short term solution... could it be that ADSL2+ is seriously congested... and that the ADSL2 equipment would serve my needs better?
The Cabinet which serves my line is due to be upgraded to FTTC by the end of November... this might lead to less ADSL congestion at the exchange as subscribers nearer to the cabinet upgrade their service...

[#7]

What a difference 80 minutes makes... lol...
Uptime: 0 days, 4:57:36
DSL Type: G.992.5 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 18,487 / 1,492
Bandwidth (Up/Down) [kbps/kbps]: 444 / 1,144
Data Transferred (Sent/Received) [MB/MB]: 12.94 / 39.46
Output Power (Up/Down) [dBm]: 12.5 / 16.0
Line Attenuation (Up/Down) [dB]: 37.0 / 64.5
SN Margin (Up/Down) [dB]: 15.5 / 3.0
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 13 / 0
FEC Errors (Up/Down): 6,272 / 1,397,108
CRC Errors (Up/Down): 12,944 / 47
HEC Errors (Up/Down): 2,220 / 41

[#8]

Changing a setting on your modem/router is not going to connect you to different equipment at the exchange. It's just going to adjust the ADSL signals transmitted over your line slightly. It may well be the best setting for a very long line such as yours, regardless of if the line is in perfect condition or in poor condition.
At the risk of getting too technical, the main difference between ADSL2 and ADSL2+ is that ADSL2 operates on frequencies up to about 1.1MHz but ADSL2+ signals go up to 2.2MHz. On a long line such as yours, none of the frequencies above 1.1MHz will be in use anyway. However that's not the only difference, and I suspect that the difference in performance between ADSL2+ and ADSL2 on long lines is just that ADSL2+ was intended for shorter lines, so the power levels on the upstream and the lower part of the downstream are reduced slightly, to reduce the impact (crosstalk) of short ADSL2+ lines on other lines when they all end up near each other at the exchange.
Some equipment, I think it depends on the exchange, would have automatically chosen to operate your line as ADSL2 (G.992.3), but yours hasn't.

[#9]

Let me explain a few things Richard as you've got the wrong end of the stick, and this has not been helped by ejs's obsession with ADSL2/2+ modes which by his own admission in reply #54 would have little effect if any at this time

Quote from: ejs

Although you wouldn't see any immediate improvement unless any banding is removed.

ADSL2 and ADSL2+ are "modes" as is ADSL1 (when all on 21CN) - the equipment at the exchange is exactly the same. Changing mode merely affects the tones that can be used and the number of bits on those tones.
Traffic at the exchange does NOT affect your SNRM - nor does your own traffic come to that.
The variations in your SNRM are symptomatic of the normal day/night variations exacerbated by the increased vulnerability due to non-twisted pair cable. There is also evidence that suggests your modem/router may be "faulty". As I have already pointed out, the standard procedure is to try another known good modem/router.
Fiddling with modes is only introducing another variable into matters and just clouds the issue.

[#10]

You would not get an immediate improvement in speed on switching to ADSL2 if the line is banded. You would probably see an improvement in the noise margin, perhaps even enough so that the line becomes more stable and holds the connection for long enough for the banding to automatically be removed. But they've probably been so many drops by now that the banding will never automatically be removed.
I don't really see what's wrong with configuring the modem/router to get the best out of the line. ADSL2 would be a better setting regardless of the presence of any other problems. Setting the D-Link to ADSL2 would probably also be a good idea. Perhaps before connecting the D-Link to the telephone line, switch it on and configure it for ADSL2, and then switch it off again before plugging it into the telephone line. And then while the 585v8 is disconnected from the line, configure it for ADSL2. That way you avoid the extra re-syncs you'd get if you had changed the mode while the modem is connected.

[#11]

To be crystal clear Richard, the only thing that ejs and myself are having a technical disagreement about at the moment is the benefit or otherwise of changing mode from ADSL2+ to ADSL2, which I'll post more about in a few minutes.
(I don't disagree btw with his suggested method of going about such a change, that is something similar to what I would suggest, I often suggest making changes to modem/router settings off-line to avoid resyncs).

[#12]

Pretty disappointing results today... I switched the router off for 20 mins at about 3:30pm...
The images herewith are not very encouraging...

[#13]

3.30 pm is too close to an hour before sunset really, background noise levels are increasing. What are your stats like?

[#14]

Quote from: Anotherone

What are your stats like?

It's difficult to know whether the stats are good or bad...
SNR is 2 and yet I have been able to download emails without the usual problem associated with low SNR, i.e. usually it is necessary to reboot the router when email fails to download...
I've also managed to download a 25mb file at 100-115 kbps...
The stats are:
Uptime: 0 days, 2:43:25
DSL Type: G.992.5 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 18,028 / 1,348
Bandwidth (Up/Down) [kbps/kbps]: 444 / 1,147
Data Transferred (Sent/Received) [GB/MB]: 89.07 / 102.98
Output Power (Up/Down) [dBm]: 12.5 / 16.5
Line Attenuation (Up/Down) [dB]: 37.0 / 64.5
SN Margin (Up/Down) [dB]: 15.0 / 2.0
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 16 / 0
FEC Errors (Up/Down): 7,905 / 1,823,040
CRC Errors (Up/Down): 145,706 / 944
HEC Errors (Up/Down): NA / 1,097

[#15]

Not good. A very high error count. Lots of errors will be reflected in poorer download speeds as well.