Sizeable difference between Actual and Attainable Rate on FTTC/vDSL

[#1]

Hi all,

I've been looking at my parent's FTTC connection as they've said it feels slower in recent times than it used to be. I've had a look at the DSL stats on the modem (a Draytek Vigor 167) and it is showing the actual rate of 32942kbps but an attainable rate of 49347kbps. This seems quite a sizeable difference as I'd expect these to normally be fairly close. Does this look like a banding issue on the line and could they get a DLM reset to see if we can get the downstream actual rate back up? A speed test is showing 30mb which seems an unusually rounded number!

Cheers,

Jeremy

[#2]

@jeremyphillips Sight of the full DSL stats would be useful. Please attach them (using the 'paper clip' icon) rather than as an embedded image. 

[#3]

@jab1 I've asked the mods to 'approve' the image half an hour ago !

[#4]

Yes of course, sorry didn't realise the image wasn't showing! Now added as an attachment 

Cheers,

Jeremy

[#5]

Thanks, @jeremyphillips . The SNR margin, which is what I was concerned about, looks OK, so that is one thing out of the equation.

I know little about the capabilities of the Draytek, but does it have a useful event log?

[#6]

Thanks @jab1 

Whilst you can set monitoring logs on the modem, this isn't running by default so nothing on there I'm afraid. It is being used as a bridge modem for a Unifi router (been in place for several years with no issues). The connection seems pretty stable from the logs on the router - there are no disconnections showing for the previous 30 days.

From what I can see (and what my parents tell me) it's been completely stable, it just seems to be running slower than it used to which led me to looking at the DSL stats directly!!

Cheers,

Jeremy

[#7]

OK, @jeremyphillips . As the SNR  margins look good (although I understand from previous comments about Draytek kit that they are not always 100% reliable), maybe if your parents contacted PN and asked for a reset, they may get a speed increase, but something has obviously happened to lose them a chunk of speed, so there are no guarantees that whatever caused the drop won't occur again.

[#8]

@jeremyphillips 

Those stats are a bit disappointing, but I doubt if the line is 'banded'.

Are the error counters (under the "Line Statistics") clocking up more errors than usual ?.

When I first had my Vigor 167, my sync vs attainable wasn't great (but wasn't as bad as your parent's)

I got some improvement by experimenting with the different "modem code" versions.

It might be worth you trying the other codes, in case something different better suits the chipset in the FTTC cabinet.

To change the settings, I did a recent post here

[#9]

@jeremyphillips 

It might be worth setting up a (free) ThinkBroadband "Broadband Quality Monitor" so you can watch a chart to see whether the VDSL connection is suffering packet loss or unusual latency patterns.

It is easiest to use if your parent's Plusnet account has a static IP address, but if they don't then you should still be able to get it to work by configuring DDNS in the Unifi router, and configuring the BQM with their hostname.

[#10]

@ExForce9 It is a long time since I had FTTC, but the d/s interleave depth looks a bit strange to me?

[#11]

The “attainable” metric is an estimate of what the line (based on its attenuation) might achieve in ideal conditions.

The “actual” metric is the real world capability of the circuit dealing with physics.  The interleaving depth (error correction) is quite significant here.  That could be to deal with cross talk.  It is worth raising a fault report on, but I suspect the line is working above the guaranteed minimum so getting traction on BTOR might be difficult.

Folks get really anal about speed in circumstances where they have no discernible issues with their use of the internet.  Is a real operational issue being experienced here?

[#12]

Hi everyone,

Thanks for all the replies so far!

@ExForce9 thanks for the suggestion for the Think Broadband Quality Checker. They do have a static IP so I've set that up and will monitor that to see if that shows anything particular

@Townman I will look at raising a fault to see if there is any issues with the line at all. I do agree that speed isn't everything and there really isn't any major issue with the speed as it is. The connection is stable and works absolutely fine, my parents had mentioned that it didn't feel as fast as it had been which is what prompted me to take a look, and then more curious about the different rates and interested to understand what that actually meant for a FTTC connection.

Out of interest I had a look back at when the connection was installed back in 2013 and found a speed test screenshot showing the download speed at 57.29mb so it has definitely declined over the years (appreciate with additional connections/demand but still seems quite a change!)

[#13]

The “physics of the environment” can change …

• cross talk from adjacent circuits (especially if they are iffy too)
• degraded crimp joints (especially if damp)
• RFI from innocuous electrical equipment (especially PSU “bricks”)
• deteriorating CFL lights (used as replacements for tungsten filament lights)

You note that it is stable - that is the consequence of the interleaving depth (at the cost of raw speed).  Note in some situations higher sync speeds can lead to lower data throughout speeds because of the increased retransmission rates to deal with error packets.  High seed is only “better” if there’s a very low error rate.

Ultimately the speed is a function of the quality of the line, the biggest challenge being the distance to the greet cabinet.