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.