Islamic Azad University
Cloud computing plays a vital role in todays distributed systems widely used by internet users. It provides a flexible and consistent environment in which the data, devices and services can be shared among end users in order to save the time and cost. The advanced computing is the most important service provided by this technology. Due to the complexity and difficulty of services requested by IT industries and organizations, cloud computing has become a widely adopted technology to expedite and facilitate the process of service delivery through internet. In the last decade, quite many researchers have focused on structures and fundamentals of cloud computing resulted in various definitions, requirements and models.