Since the launch of the Home 1Mb 50:1 product, there have been serious
speed issues on some local exchanges.
A fair amount of these problems are down to the way in which the equipment
was dealing with contention, and many 1Mb users found their speeds almost
down to 512kb speeds.
It seems that the CISCO RAS (equipment that controls the flow through
the VP) installed in a lot of exchanges has no way of distinguishing
between a 512kb and 1Mb connection, and is serving all users an equal
amount of available bandwidth... regardless of connection type.
(It is the line card that determines your maximum speed).
Therefore if the Virtual Path at the exchange is coming under pressure,
the 1Mb users are seeing the effects first.... after all a 512kb user
may not notice a speed drop to say 420 kbps but a 1Mb user certainly
BTw are resolving these issues by carrying out work on exchanges which
have been identified as having a problem.
One solution is to increase the bandwidth on the VP if there is any
spare (not always possible).
Another solution would be to replace the CISCO gear with Juniper ERX's,
which are able to differentiate between a 512kb and a 1Mb connection,
and ensures that a 1Mb user would get twice the available bandwidth
than the 512kb user.
BTw released a list of exchanges which are due to be upgraded and you
can check the status of your exchange from the Plusnet checker here