#mdns

MDNS

MDNS is Multicast DNS - a local-network, decentralized, DNS. What this allows for is things like routing http://AppleTV.local calls to the Apple TV on the local network. How? All the devices that want to allow access via this URL broadcast to a known location, saying they will be known as DeviceName.local - When a call needs to be made to DeviceName.local, there is a local resolution of the IP address: “Hey, raise your hand if you are DeviceName!”

DNS-SD

This is similar to the MDNS setup, but instead devices announce capabilities. Devices or applications will again broadcast to a known location on the network and say what they support: HTTP Server, Printer, AirPlay, AirPlayAudio, etc. When something like a printer discovery service or an iPhone needs to find a certain type of service, they ask: “Who here can print things?”

AirPlay

AirPlay servers announce two things, their name on the network and their capabilities. Your phone then jumps through the hoops to find the devices that can accept airplay and their location on the network (IP and Port of the service). Once the resolution has been made, the fin begins. Simple things like playing a video are just a HTTP POST - http://AppleTv.local/play with a payload specifying the URL of the video.

Light Reading

ZeroConf/DNS-SD

Multicast DNS