Peer to Peer Airplay

If you have a TV connected to an AppleTV and an iPhone, iPad, or a Mac computer, you can use the built-in Airplay feature to have the TV display exactly what is displayed on the iPhone or iPad. In short, what you see on the iDevice (a generic name for any portable device that runs iOS), you can see on the TV.

There are 2 ways to setup this projection: Infrastructure and Ad-hoc.

Infrastructure is when both the AppleTV and iDevice are connected through a middleman such as a wireless router. This means all Airplay traffic between the AppleTV and iDevice go through the centralized controller that is the router. While this certainly makes setting up easier and consistent, it does require an extra piece of hardware and the speed decreases because of the connection between the AppleTV and iDevice is indirect. There is also a slight performance degradation as well if you plan to project a video, resulting in some stuttering. Therefore, if you plan to stream videos that are already stored locally on the iDevice, then an ad-hoc or peer to peer connection is recommended.

The article below from Apple explains in technical details what is happening during a peer to peer Airplay connection between an AppleTV and an iOS portable device.

http://help.apple.com/deployment/ios/#/apd8fc751f59

Basically, for peer to peer Airplay to work, you need to have the required hardware. On the AppleTV end, it has to be a 3rd generation rev A Model A1469 or later with AppleTV software 7.0. On the iDevice end, it has to be a model made in 2012 or later with iOS 8. If you want to use a Mac computer instead of an iOS 8 device, then the requirement is a Mac computer made in 2012 or later with OS X Yosemite version 10.10.

Basically the AppleTV and iDevice use Bluetooth to make the initial connection. After that, wifi is used to do the actual mirroring. This means the iDevice cannot connect to another wifi signal that has Internet access. Therefore, if you want to play a video from the iDevice and have it be seen on the TV, then this video must be stored locally on the iDevice. If the device is a Mac computer running Yosemite, this is not a problem in terms of simultaneous Internet access because the computer has both wifi and wired connection. The wired connection is used for the Internet connection while the wifi one is used for the Airplay.

If you must use an iOS8 device and still need Internet access at the same time, then you have to use a physical adapter such as one below. Then it's no longer Airplay but just a wired connection to the TV directly bypassing the AppleTV altogether. This wired connection obviously removes the benefit of mobility of the iDevice. It has to stay fixed next to the TV.

http://store.apple.com/us/product/MD826ZM/A/lightning-digital-av-adapter

http://store.apple.com/us/product/MD098ZM/A/apple-digital-av-adapter

Incidentally, the Lightning or 30-pin female connector on this adapter is used to charge the iDevice while it is being used to project the video. This is recommended if the video is played for hours so there is a drain in battery power on the iDevice.

For those technically minded, the wifi channel used during mirroring is 149 in the 5 GHz band and channel 6 in the 2.4 GHz band. Given that video streaming takes up a lot of bandwidth, during the streaming, any other wifi devices that use these frequency will see a major degradation in their usage. This is not a problem because if you have the required hardware listed to do this peer to peer connection, then the AppleTV and iDevice will be using the 5GHz band to do the transmission instead of the 2.4GHz. The fact that there are 8 non-overlapping channels (compared to 3 channels for the 2.4GHz) to choose from for the 5GHz band, interference with other wifi devices in the area is minimal.