Back on-topic....
I think there's a bug in the version of f/w for the SR102 I listed earlier in the thread.
We'll see in a couple of days but I reckon that after a certain amount of time connected the WAN port no longer has the IP address lease renewed. After six consecutive attempts (IIRC) have failed then the router will tear down the MER interface (ptm0.1) and reconnect (holds sync throughout). It fails to get an IP lease & then sits there "sulking" until you reboot the router. Looks like a buffer overflow issue to me but with no ssh access to the router who knows?
I hear "rumours" that there's also issues with the DSL firmware as well but I'm not totally clear as to whether the issues are with ADSL, VDSL or both or in fact whether that's limited to the Sagems.