Wake On LAN (WoL)

Some time ago, a hardware capability named “Wake On LAN”, or ‘WoL’ was explained to me, which was based on an Ethernet network. According to that explanation, a number of computers at a workplace could be powered down – shut down – but their Ethernet cards would still be receiving a trickle of current from their power supplies. And then, just before the workforce would show up to begin their day, their switches and routers would send out a so-called “Magic Packet”, which would cause all the computers to boot up, and then to be ready for the workforce when it arrives for work.

Well I was recently surprised – though pleasantly surprised – to find out that a homologous feature does after all exist for WiFi, which has also been referred to as Wake On LAN, or WoL, even though the WiFi version of it does not work exactly the same way. For our WiFi-connected phones and tablets, when they are in standby, their WiFi antennae are typically still powered up, and when those receive their magic packet, it wakes them up from standby.

This is a hardware capability, which also explains why such devices are really able to receive push notifications.

I had previously explained to my friends, that with Android or iOS, instead of each app listening forever on a port number for a push notification, this capability has been centralized into the Application Framework, as part of the O/S effectively. But this being centralized to one port number for the device, would still not have been completely enough to explain push notifications.

Well apparently, in the WiFi version of this feature, the magic packet is also sent to a specific port number, which means that it can wake up a device which is behind a firewall.

And then that way, cell phones on their broadband data instead of on WiFi, also retain their IP numbers, and can thus also receive push notifications easily.