The Internet functions through a series of network protocols that form a stack of layers, as shown in the figure (or as described in more detail in the OSI model). Once an Internet connection is established among several computers, it is possible to share services within any one of the following layers.
Cloud computing can come in many forms depending on the type of service it provides. It is broadly classified as :
Software as a Service - SaaS
Cloud application services or "Software as a Service (SaaS)" deliver software as a service over the Internet, eliminating the need to install and run the application on the customer's own computers and simplifying maintenance and support. People tend to use the terms ‘SaaS’ and ‘cloud’ interchangeably, when in fact they are two different things. Key characteristics include:
• Network-based access to, and management of, commercially available (i.e., not custom) software
• Application delivery that typically is closer to a one-to-many model (single instance, multi-tenant architecture) than to a one-to-one model, including architecture, pricing, partnering, and management characteristics
• Centralized feature updating, which obviates the need for downloadable patches and upgrades.
Example: Google Apps, Salesforce.com
Platform as a Service - PaaS
Cloud platform services or "Platform as a Service (PaaS)" deliver a computing platform and/resolution stack as a service, often consuming cloud infrastructure and sustaining cloud applications. It facilitates deployment of applications without the cost and complexity of buying and managing the underlying hardware and software layers.
Example: Google AppEngine, Microsoft Azure
Infrastructure as a Service - IaaS
Cloud infrastructure services, also known as "Infrastructure as a Service (IaaS)", delivers computer infrastructure - typically a platform virtualization environment - as a service. Rather than purchasing servers, software, data-center space or network equipment, clients instead buy those resources as a fully outsourced service. Suppliers typically bill such services on a utility computing basis and amount of resources consumed (and therefore the cost) will typically reflect the level of activity. IaaS evolved from virtual private server offerings.
Example: OpenNebula, Eucalyptus, Amazon S3, EC2
Data Storage as a Service - dSaaS
Cloud Data Storage services, also known as “data Storage as a Service (dSaaS)", delivers robust, cloud-based suite of storage - as a service.
• Reduced risk through secure backup, storage, information protection.
• Reduced costs through the elimination of capital investments for archived digital storage.
• Rapid access to information for legal discovery, regulatory compliance, audits, business continuity and disaster recovery
Everything as a Service - EaaS
Through the cloud, everything will be delivered as a service, from computing power to business processes to personal interactions. The enterprise could contact a specific vendor if they wanted to implement some cloud computing processes in their business setting. As long as the business knows what they specifically need from the vendor, the services related to cloud computing could be easily set up and launched in no time.
• Decreasing dependency on the hardware – as more and more applications are used in the cloud, it has become important for the service providers in EaaS to keep everything accessible. Any service in the cloud could be accessed online without relying on one gadget that stores the native application.
• No Specific Location – EaaS is not just an application limited to certain location and gadgets. Providers will allow access from any type of gadget from any location as long as the user has the right credential (username/password) to use the system.
• Improved Tenancy – access of the system is not only limited to a number of users. The user will have the ability to get everything done on time through collaboration.
• Extension to Consumers – this type of service is not only limited to businesses. Cloud computing through EaaS is now available to consumers.
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