@Marvin_S many thanks for the reply, and apologies for the delayed reply.

The DSL light stays lit at all times, and the Mikrotik firewall/router on my side of the TD-W9960 never shows the PPPoE link going down. 

All I see (and the ISP sees) is occasional 5 second outages.

I haven't tried putting the TD-W9960 in router mode, as I've not yet had the time.  I've previously reset the modem, and the splitter is build into the wall port.  The VDSL service worked perfectly with the previous ISP who supplied their own router; I've had to supply my own bridge to work with the new ISP.

Thanks again.

Paul

  @Marvin_S 

 Thought I'd just follow this up. 

It's definitely the TD-W9960 at fault, having replaced it with a DrayTech in bridge mode which does not exhibit the fault.  Putting the TD-W9960 back in circuit, the issue reappears within 24 hours.  Going back through my ISP's logs, the TD-W9960 was fine for the first 4 months of service, and this issue has only started in the last 50 days and only affects the TD-W9960.

As the TD-W9960 is less than a year old, I'm assuming TP-Link will will replace, or similar.

Thanks again for your input.

P