DLNA + UPnP allows you stream media from mobile phones, laptops to compatible HDTVs. But you will find plenty of steps involved. Mostly, these solutions are complex enough for any typical home user. But Chromecast uses UPnP and DIAL protocol to eradicate intrication.
DIAL (Uncover And Launch Protocol) uses UPnP (Universal Plug N Play) protocol for network element discovery. Upnp multicasts and probes for available audience and senders on the given local Wi-fi compatability network. So basically moment clicking Chromecast icon on Chrome tab or android device, it probes and finds out First screen DIAL server (Chromecast device blocked to High definition tv within this situation). Once discovered, it synchronizes information about how for connecting into it.