Hi Graham.
Try Wikipedia for “Wake on LAN”: the article is quite good.
Some comments on the Wikipedia article:
"E_nsuring the magic packet travels from source to destination:_
For example, in the router, the computer to be controlled needs to have a dedicated IP address assigned (aka a DHCP reservation). Also, since the controlled computer will be “sleeping” except for some electricity on to part of its LAN card, typically it will not be registered at the router as having an active IP lease."
NOTE that DHCP reservation != manually allocating a static address to the NAS (static != reserved).
I guess “the router” for you is the Swisscom Box…does it do “reservations” (my router does, but is not Swisscom so I can’t answer).
“Other machine states…”
My NAS, 20cm from my non-Swisscom router (and around 900cm from where I usually sit) REGULARLY appears to fail to wake on LAN…but it is only the NAS wake-up delay: if I try again N seconds later it works fine. (N seems to be some positive exponential function of my blood-pressure).
“Wake on Internet”
A short section that might suggest a solution to your issue.
For humour (???), this section includes “some routers permit a packet received from the Internet to be broadcast to the entire LAN.”…mmm, that would be outright stupid, but would probably solve your issue for the 20 minutes before you lost everything.
Chris
EDIT corrected forgotten-italic & "