III. WHAT is CLOUD COMPUTING?
Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction [11],
Cloud computing represents a major shift in information technology (IT) architecture, altering the way IT services are sourced and delivered. Software and information are provided to computers and other devices on-demand, like a public utility. Consumption is billed on a utility or subscription basis with little or no upfront cost, creating a low barrier to entiy. This new approach reduces upfront capital expenditures but there may be extra cost for operating expenses.
A. Cloud Computing Service Layers
Cloud computing providers provide different kinds of services to cloud computing consumers. The cloud computing service model has three different service layers (See Fig. 2) or categories also known as the cloud stack [12]. The cloud computing service layers are briefly explained in the following: