Airplay doesn`t work on my Macbook Air (mid 2011)

Please help me.. No icon showing up on status bar, no airplay icon in iTunes. But everything works fine mirroring iPhone and iPad to Apple TV on exact same network. and music airplay from itunes on my old 2007 iMac also working.

When i look up specs on my MBA it says (mid 2011) this should work. What can be the problem??