We are hearing from more and more users who are experiencing very slow Broadband, particularly users who connect to the Corfe Castle exchange — we have had reports from PlusNet, Mad as a Fish and Virgin users in Church Knowle, Kimmeridge and Harmans Cross — they’re at least 2+ miles away from the Corfe Castle Exchange, and have also reported random noise on their telephone lines.

A helpful support person confirmed that they have had to turn on ‘Interleaving’, which appears to help, but there are several drawbacks to using this.

What is Interleaving?

Interleaving is a form of error correction that can help reduce the number of ‘errors’ on a line. This will be activated by default on new broadband services and where a fault has previously been reported. It helps to stabilise a line that might otherwise suffer frequent disconnections. One drawback of interleaving is that it can increase ping times, which may cause problems for people that play online games. Whilst we’d recommend against it, if it is switched on, interleaving can be turned off if you ask us.
Source: PlusNet

Traditionally adsl used what is known as “FAST” method for transmitting data.
MaxDSL & LLU can make use of a technology called Interleaving to help maintain the tolerance against noise on longer length lines.

If during transit more than a certain amount of data has been lost then the data cannot be correctly decoded by your router. Short bursts of noise on the line can cause these data packets to become corrupt and the modem has to re-request data which in turn can slow down the overall rate at which data is transmitted.

Interleaving is a method of taking data packets, chopping them up into smaller bits and then rearranging them so that once contiguous data is now spaced further apart into a non continuous stream. Data packets are re-assembled by your modem.

If your line is particularly susceptible to bursts of noise then interleaving should improve your adsl experience simply because if you lose a whole batch of data then this could cause your modem to loose sync with the exchange.

By now you may be asking if interleaving is so good, then why isn’t it used by default?
The answer to that is that it can also have a downside – chopping up, rearranging and decoding of the data adds a small amount of additional time it takes for data transmission. Forward Error Correction will also add to the delay, since the check bytes will take additional transmission time.

BT state that interleaving can increase latency by an additional 20-40ms. Whilst this will not be noticeable to the vast majority of users, ardent gamers are the ones most likely to complain about additional latency and therefore prefer a slower synch speed than higher latency.

It should also be pointed out that whilst BTw state that applying interleaving shouldn’t reduce your line speed, it does reduce the maximum line rate achievable from 8128kbps to 7616kbps due to the additional overhead required for check bytes.
Source: kitz.co.uk

We would be interested to hear from anybody who is experiencing very slow Broadband in Purbeck. We would also be interested to hear what ISPs are saying is causing the problem(s) and how they are fixing them.

Note: Remember to turn your Router off/on and check all cabling before calling your ISP, you can guarantee they will ask you to do this first before they investigate the problem!