What's causing iMac to seemingly randomly come out of sleep mode?
Ever since I first got my Mavericks iMac, which was about a year ago now, and set it up, it's had the annoying habit of coming out of Sleep mode occasionally all by itself. When it does so the screen remains black but the iMac re-establishes its Ethernet connection with the router. To date, I've never found a convincing explanation for this. I find it somewhat concerning. But possibly the way it's working is correct? So, I'm wondering if anyone else has observed this.
There are several forms of Sleep mode, I gather (I've read Apple's notes on Sleep mode). This is the one where, having finished a session on the Mac, I select the Apple menu and, rather than clicking on Shut Down or Restart, I click Sleep. This blanks the screen and, as I understand it, leaves the machine in an activated but low-power condition. It also, after a delay of about 7 secs, automatically disconnects from the Ethernet interface (wired, in this case) with the router. This is observed by means of the Ethernet port indicator on the router. To resume work on the machine, a press of a keyboard key or a click of the mouse is all that's needed, and the Ethernet connection then also automatically resumes.
It all works okay, apart from the Mac from time to time coming out of sleep mode all by itself, including re-establishing the Ethernet connection - but with the screen still blank. As an on-the-spot remedy I then use the mouse to bring the Mac fully out of sleep, ie. I bring the screen back, then put it back to sleep again. This oddity happens completely randomly (or so it seems), about twice a week on average.
I've analysed all my power, UPS and screensaver settings and I use no remote services, but have thus far failed to pinpoint the cause. I've also read Apple's published notes on Sleep mode but none of their suggested possible causes seem to fit.
The only explanation I can come up with is that perhaps from time to time the Mac decides to do a backup, despite being in the Sleep state. I run Time Machine, backing up to an external USB-connected SSD. But if that's correct and valid, why should it also re-activate the Ethernet connection to the router?
Can anyone come up with a better explanation?
iMac (27-inch, Late 2013), OS X Mavericks (10.9.2)