Mine: A1427. Software 7.2 (7512). Connected via Wi-Fi.
I usually put mine to sleep manually, but I have also observed it when ATV puts itself to sleep (set to sleep after 1 hour.) Does not seem to make any difference how it sleeps.
Once mine goes into this "deep sleep", I cannot "see" it in Airplay on any of my iOS devices, or in iTunes on the PC. Sometimes it does show up in iTunes, but when I connect, it fails, and when I deselect ATV, it then disappears from the airplay list in iTunes.
If I ping it with a -t and then use a WOL program to send Wake on LAN command, then it wakes up. The blue light stays off, and there is no video output. So it is like there are 3 different levels of "awake-ness" on the ATV:
1) Full power
2) regular sleep (no blue LED on front, no video output, but visible in Airplay, and responds to ping)
3) "deep sleep", which is the one where it is not ping-able, will not be visible in Airplay, cannot connect to it with itunes. The "deep sleep" mode requires me to ping and use WOL to wake (or use ATV silver remote to wake it up to full power.)
I just want the ATV to never go into deep sleep. I want it to stay pingable, and visible in Airplay, just like it used to before one of the ATV software updates changed the behavior. The fact that it responds to WOL when in deep sleep is interesting. It's almost like Apple wants it to to that?
Also, I used the command dns-sd -B _raop._tcp in windows cmd line, and it shows the Instance Name of the ATV, but the MAC address is off by one digit! (Last digit in Instance Name is "8", but on ATV unit, in settings-> about, it shows a "7", and the arp table shows "7" as the last digit as well. Weird.
My router is a Linksys E1700.