Very High SNR, therefore low sync speed

Some friends have just moved house, and are using the same t/p link router (on BT) they had at the old place

Upstream is as I'd expect, but downstream the Max Attainable rate is 14 Mb/s, but actual Sync Rate is only 4.5 Mb/s, the SNR is a ludicrous 26dB

........................ Upstream....... Downstream
Current Rate(kbps) 1279......... 4544
Max Rate(kbps) 1316........ 14140
SNR Margin(dB) 7 ........ 26.4
Line Attenuation(dB) 17.8 ......... 31

Will the line eventually train to a 6dB SNR, and therefore increase the sync rate towrads 14 Mb/s ?

FTTC or ADSL2+ ?

Suspect long line FTTC. How long has the line been active with the service? Since FTTC should pretty much start close to the max speed and only slow down if errors are bad, rather than start with a very high margin and then reduce margin slowly.

In reply to a post by MrSaffron:

FTTC or ADSL2+ ?

Suspect long line FTTC. How long has the line been active with the service? Since FTTC should pretty much start close to the max speed and only slow down if errors are bad, rather than start with a very high margin and then reduce margin slowly.

No, it's ADSL2+. Been activated 48 hours

I'd be tempted to check the socket, filter, cable, etc. since something is not seeming quite right. Unfortunately, TP-Links tend to have very limit stats available to the end user, so it might be tricky to see any obvious from this perspective. Depending on the type of socket, you may want to try the test socket to see if it makes any immediate difference (since the test socket bypasses any wiring on the faceplate). See more here.

In reference to your comment regarding your sync speed and SNR, the majority of ISPs have DLM that start off with low SNR and adjust as necessary to balance with the stability profile in place. The exception was (and probably still is) Sky (LLU) as from memory they used to start of at 4 Mbps and work way up if possible.

Edited by deleted (Sat 02-Mar-19 16:10:40)

Thanks J0el. They are 100 miles away, and non technical, but I'll monitor their router and next time I'm down there take a look. I suspect the extension sockets could be hard wired to the back of the master socket. They know to use filters on all extension devices. but I'll take down a filtered faceplate when I visit, that would be good practice regardless.

They report the connection is perfectly stable ( and I can see that too from the TB BQM graph I have running)

An update, the downstream speed is increasing, in jumps every 48 hours.

On Monday morning it jumped from 4.5 to 6.7 Megs (SNR dropped from 26 to 21 dB)
This morning (Weds) it's jumped again up to 9.8 Megs (SNR now 15dB)

Max Obtainable remains constant at just under 14 Megs, and upstream actual and max both around 1.2 Megs

No sign or evidence of connection 'distress'

....Another 48 hours, and now

D/S is 14.3 Mb/s (Max Obtainable is 16.2) SNR 8.5 dB

U/S is 1.27 Mb/s (Max Ob 1.31) SNR 7dB

The common theme is there is (according to the BQM ping graph) a brief
disconnection at around 4am every 48 hrs that seems to be the point
the d/s speed takes another upward jump.

It is good that the situation is improving without any intervention. Seems the DLM sees connection stable. Can't say for definite why SNR would have been so high on a new activiation. It is definitely BT?

In reply to a post by j0el:

It is good that the situation is improving without any intervention. Seems the DLM sees connection stable. Can't say for definite why SNR would have been so high on a new activiation. It is definitely BT?

Oh yes, it's BT, BT Retail is the ISP, on a non LLU small rural exchange.

Another step change at 4am this morning.

Max rate now 17.8 Megs, download 14.5 Megs, SNR 6dB, but the latency has doubled, so presumably
interleaving has kicked in ? Good job they're not gamers !

In reply to a post by broadbandjockey:

Max rate now 17.8 Megs, download 14.5 Megs, SNR 6dB, but the latency has doubled, so presumably
interleaving has kicked in ?

Unless the line is capable of 3 dB (is clean) then this may be around the most it'll get to. Either way, performing on par with what is expected with the attenuation.

Without seeing stats, possible that interleaving has been instated. Increase in latency is usually a sign, though sometimes it can be down to routing (can't comment on BT's routing). Perhaps there were quite a few Errored Seconds being counted, but interleaving should help stablise things.