Which of the following examples best describes the SaaS service model?

A. A company obtains a subscription to use a service provider’s infrastructure, programming tools, and programming languages to develop and serve cloud-based applications.
B. A company moves all company-wide policy documents to an internet-based virtual file system hosted by a service provider.
C. A company hires a service provider to deliver cloud-based processing and storage that will house multiple virtual hosts configured in a variety of ways.

D. A company licenses an office suite, including email service, that is delivered to the end user through a web browser.

Explanation:
A company that licenses an office suite, including email service, that is delivered to the end user through a web browser is an example of the Software as a Service (SaaS) service model. The National Institute of Standards and Technology (NIST) defines three service models in its definition of cloud computing: SaaS, Infrastructure as a Service (IaaS), and Platform as a Service (PaaS). Cloud computing offers several benefits over traditional physical infrastructure and software licensing, including a reduction in downtime and administrative overhead.
The SaaS service model enables its consumer to access applications running in the cloud infrastructure but does not enable the consumer to manage the cloud infrastructure or the configuration of the provided applications. A company that licenses a service provider’s office suite and email service that is delivered to end users through a web browser is using SaaS. SaaS providers use an Internet-enabled licensing function, a streaming service, or a web application to provide end users with software that they might otherwise install and activate locally. Web-based email clients, such as Gmail and Outlook.com, are examples of SaaS.
The PaaS service model provides its consumer with a bit more freedom than the SaaS model by enabling the consumer to install and possibly configure provider-supported applications in the cloud infrastructure. A company that uses a service provider’s infrastructure, programming tools, and programming languages to develop and serve cloud-based applications is using PaaS. PaaS enables a consumer to use the service provider’s development tools or Application Programming Interface (API) to develop and deploy specific cloud-based applications or services. Another example of PaaS might be using a third party’s MySQL database and Apache services to build a cloud-based customer relationship management (CRM) platform.
The IaaS service model provides the greatest degree of freedom by enabling its consumer to provision processing, memory, storage, and network resources within the cloud infrastructure. The IaaS service model also enables its consumer to install applications, including operating systems (OSs) and custom applications. However, with 1aaS, the cloud infrastructure remains in control of the service provider. A company that hires a service provider to deliver cloud-based processing and storage that will house multiple physical or virtual hosts configured in a variety of ways is using IaaS. For example, a company that wanted to establish a web server farm by configuring multiple Linux Apache MySQL PHP (LAMP) servers could save hardware costs by virtualizing the farm and using a provider’s cloud service to deliver the physical infrastructure and bandwidth for the virtual farm. Control over the OS, software, and server configuration would remain the responsibility of the organization, whereas the physical infrastructure and bandwidth would be the responsibility of the service provider.
A company that moves all company-wide policy documents to an Internet-based virtual file system hosted by a third party is using cloud storage. Cloud storage is a term used to describe the use of a service provider’s virtual file system as a document or file repository. Cloud storage enables an organization to conserve storage space on a local network. However, cloud storage is also a security risk in that the organization might not have ultimate control over who can access the files.

Reference:

Cisco Press CCNA Data Center DCICT 200-155 Official Cert Guide, Chapter 15: Cloud Computing, Cloud Computing Service Models, pp. 574-577