The IOT Internet of things is rapidly moving towards reality. It is broadly applied to plenty of areas which includes healthcare, smart homes, smart cities, energy management, logistics and to forth. Smart homes are distinct class of IOT environments with a variety of connected heterogeneous devices. Daily life entities connected to the internet are enriched with the capabilities of identifying, sensing and processing. The heterogeneous entities require to execute mutual performance of activities effectively & rapidly. However, with the huge growth of connected devices, the ability of interoperation among devices is going to be a challenge. In this paper a state of the art on interoperability in smart homes is presented. The detailed discussion is given on numerous feature of connectivity protocols used for interoperation, limitation of existing solutions encounters in research.