By default, Windows 7 supports network card offloads —Address Resolution Protocol (ARP) and Neighbor Solicitation (NS)— that allow the network card to maintain and renew the address lease and routing information about that PC while the PC is in a low-power sleep state. Unlike when using Wake on LAN (WOL), the PC is addressable via its IP address and does not require data be sent to the broadcast address before it gets routed to the sleeping host. Hence, when the ARP and NS offloads are active, a remote desktop connection can be made to a sleeping host with only an IP address – the same information normally used to establish a remote desktop connection! Please note that this is not simply a windows feature but it is support for a hardware feature that has been standard on all new PCs since 2011. This feature is supported in some machines going back almost circa 2006 and most systems purchased since 2010.
Look here for more information on this feature .