Max Available FTTC Broadband Speed decreased by nearly 25%

I've been with PlusNet since October 2012. I signed up for their £19.99 Fibre package. I was told that the maximum available speed would be 48mb/s from my Haywards Heath exchange.

My fibre was installed in October and it has been running a 48mb/s up until a month ago. The ping rate has doubled and my speed tests reveal my connection is running at 37mb/s.

Having raised this with PlusNet they have advised that the maximum available speed has now been reduced from 48mb/s to 37mb/s. Currently they are not able to tell me why this is the case other than it is like to be line degradation.

Don't get me wrong 37mb/s is a good speed, it's more the principle of the matter that the speed I'm now getting is not what I was promised by PlusNet 8 months ago. Who is to say BT won't reduce it further?

PlusNet made it clear when I signed up that my connection speed would be much more reliable and the speed quoted is the speed I would get.

Does anyone on here have a view as to the above?

The sales people should perhaps have been a bit more circumspect on the estimate

If lower speed and higher latency looks like the DLM system that ISP has no control over has decided to slow you down to reduce errors

Thank you for your reply. If I understand your reply about errors. In the 8 months I've had FTTC its been a very reliable service, no cause to complain and very happy. I'm always streaming radio or TV and it has been excellent, no problems with the service at all.

I'm just not happy that they can lower the speed without notifying customers. You've paid for a promised service/speed and now not getting it. These companies make a big deal of telling you what speed you will obtain and that it is accurate to +1/-1 mb/s on the availability checker, but when it drops by 11mb/s thats a substancial amount.

Sorry, a little frustrated with the way these large companies can do what they like!

Please can you run this speed test, make a note of the latency figure, then clck the Further Diagnostics at the bottom.

That will ask for your phone number then give you the old style text boxes with download and upload speeds and IP Profiles. Please copy and paste the full contents of each of those boxes .

It will be to keep your line stable, if they send say a 100mbps down your line and it can only take 50mbps you will get packet loss high jitter disconnections, if you use a headset for gaming it would be popping and cracking the game would lag, it would disconnect all the time, it would be unusable so they slow it down to keep your line running smooth.

Hi.

Below is the output. Hopefully this is what you require. The ping used to be 8ms but its now at 22.38ms

Results.

1. Best Effort Test: -provides background information.

Download Speed
38.26 Mbps

0 Mbps 40.78 Mbps
Max Achievable Speed

Download speedachieved during the test was - 38.26 Mbps
For your connection, the acceptable range of speedsis 16 Mbps-40.78 Mbps .
Additional Information:
IP Profile for your line is - 40.78 Mbps

2. Upstream Test: -provides background information.

Upload Speed
10.19 Mbps

0 Mbps 20 Mbps
Max Achievable Speed

Upload speed achieved during the test was - 10.19Mbps
Additional Information:
Upstream Rate IP profile on your line is - 20 Mbps


We were unable to identify any performance problem with your service at this time.
It is possible that any problem you are currently, or had previously experienced may have been caused by traffic congestion on the Internet or by the server you were accessing responding slowly.
If you continue to encounter a problem with a specific server, please contact the administrator of that server in the first instance.

In reply to a post by prayme68:

I'm just not happy that they can lower the speed without notifying customers. You've paid for a promised service/speed and now not getting it.

You've paid for an "up to" speed not a guaranteed speed.

As mentioned, they haven't lowered your speed it's all done automatically to maintain line stability. Generally the speed will drop as more people get connected and the effect of crosstalk start kicking in.

In reply to a post by prayme68:

I was told that the maximum available speed would be 48mb/s from my Haywards Heath exchange.

Were you told a "maximum available speed", or given an estimated speed?

The term "maximum available" or "maximum attainable" speed is something very specific, and indicates what the modem thinks is the maximum speed it is capable of at any moment in time. It is NOT generally the same as the estimated speed given to you by an ISP at the time of sign-up.

What is your estimated speed at the moment?

You can get one answer from this Plusnet portal page, and you might as well post the "current line speed" too.

You can get another answer from BT Wholesale, on their DSL checker. These estimates are actually the source of the Plusnet estimates, and BT have recently reduced them all a little.

The ping rate has doubled and my speed tests reveal my connection is running at 37mb/s.

It looks like your line has indeed had DLM (dynamic line management) intervention, after the cabinet has detected errors on your line. You probably won't have been aware of these errors, but the modems *are* aware, and keep track of the numbers.

When DLM intervenes, the first step it takes is usually to turn on two processes known as "interleaving" and "forward error correction". The aim is to get rid of the errors - but the effect is that it uses around 20% of your line's capacity (ie reduces speed by 20%) and adds at least 8ms to the latency. If enough errors still exist on the line, the level of interleaving and FEC are turned up, but at the cost of even more speed and latency.

Where have these errors come from?

You may have been suffering from some errors all the time, or they may have increased gradually. One source - the major source now - is from other subscribers to FTTC (whose signals to their modems act as extra noise to your modem). It is generally expected that speeds will drop as take-up increases - and in a very random way.

This effect is known as crosstalk.

Currently they are not able to tell me why this is the case other than it is like to be line degradation.

Good job we're here to help then. You'd probably get similar information by posting on the Plusnet community forum too.

Who is to say BT won't reduce it further?

Absolutely nothing. BT runs the system to get rid of errors as much as possible - they are very much aiming at stability over out-and-out speed.

On the upside, BT are starting to trial some new technology that aims to remove the effect of crosstalk from the FTTC lines. watch out for news on vectoring, but don't expect this to appear anytime in the next 2-3 years.

PlusNet made it clear when I signed up that my connection speed would be much more reliable and the speed quoted is the speed I would get.

They're almost certainly right with the reliability, but no-one can yet do anything about the crosstalk.

In reply to a post by prayme68:

Sorry, a little frustrated with the way these large companies can do what they like!

There isn't a lot the companies, large or small, can do about the laws of physics.

On my first line, DLM kicked in on day 3, because from day 1 it encountered 4-5% errors packet loss due to errors. That rate of errors was enough to reduce throughput speeds by 10-15%, so the reduction in sync speed caused by the DLM intervention didn't actually have any impact on the overall throughput I saw during speedtests.

At our new house, the line has stayed in better shape. However, over 18 months the "maximum attainable" value reported by the modem has gradually dropped over time, starting at 90Mbps and dropping as low as 73Mbps.

Edited by deleted (Fri 07-Jun-13 00:52:52)

Yes . Just what I asked for.

Those figures show that the speed decrease is due to the Openreach FTTC system itself, as your sync (connection) speed is now approximately 42.13Mbps. (Calculated from the IP Profile). We can also see that you are still on the PlusNet "up to" 80/20 product and have not been restricted or downgraded for any reason or by mistake.

The two intermediate posters have covered the typical reasons fro this sort of speed loss. I lost about 10Mbps and gained an extra 8ms latency just over a year ago, because interleaving was introduced on my line after 12 months at the higher performance.

Another point is that at the time you got your orignal estimate I believe those were based by (Openreach) on sync speeds. I think the ASA or Ofcom now require them to be based on speedtest type figures, which are always lower.

So bad news, but the same for many of us. Part of the downside of us getting this sort of speed down copper wires that 10 years ago couldn't go at a tenth of what they do now.