Dark Servant wrote:

I'm running a Billion 5100 router with a 256/64 Dodo ADSL plan and I've noticed 
that every now and then disconnection occurs

Hi Ruben,

How often? Once a day, once a week, less often? 1 or 2 disconnections a month is normal. Disconnections can occur for the following reason
- Telstra doing work at the exchange
- Unplanned/planned issues at the ISP
- Interference on your specific telephone line
- Busted modem/router
- Busted ADSL port on the DSLAM at the exchange

If the disconnection is more regular, ie every few minutes, then I would look at something local, ie damaged phone cable, no filters on phones, dodgy filters.

Most of the time the PPP light just goes out and doesn't come back on till 
later but this time it was alternating to being on and off every now and then.

Again, how often is "now and then"? Do you lose sync as well, or just PPP connection? If just PPP connection, the logs on your router should tell you why it disconnected.

Only real reason for that setting is to save on costs though. I'm assuming 
while I'm disconnected the router is continually dialling up trying to get me a 
connection

ADSL does not make telephone calls, thus there is no charges for connecting/disconnecting. ADSL works on a different frequency to normal telephone calls.

--
Regards

Trevor Lee
Highway 1 Internet Solutions