it seems that tp-link didn't enable this on C3200.
for the disconnection, it happens on all the devices? wireless or wired?
any new device joining before problem happens?

Thanks for the reply. Shame TP-Link didn't enable this on the C3200, wish I'd never sold my Asus!

Its actually the C3200 that disconnects, I can be see the orange internet light come on every time it happens, I'm pretty sure the modem DSL light goes out too. I've noticed my download speed has dropped from nearly 74Mbps, to just over 59Mbps. There have been no new devices connected to my network either, no network configuration changes, I'm pretty sure there is a problem with the line, for which I'm waiting a reply about from my ISP.

if the dsl light goes out too at that time, there is something related to the isp side, i think