Internet of things technology is delivering new experiences to the people by connecting devices, people and networks together. Examples include smart grid, smart health, smart home, smart offices, smart manufacturing, e-commerce, e-governance and smart industrial control. More and more devices are connecting every day resulting in more security threats and issues. We need a robust IoT security model to support resource constrained IoT devices, and end to end security. In this paper, we have discussed the entities involved in providing IoT based services for example IoT devices, applications and networks.