*2.4.2 Platform-as-a-service (PaaS)*

The capability provided to the consumer is the deployment of consumer-created or acquired applications created by means of programming languages, libraries, services, and tools supported by the PaaS provider. The consumer does not manage or control the underlying cloud infrastructure, including network, servers, operating systems, or storage, but has control over the deployed applications and possibly the configuration settings for the application-hosting environment.

**Figure 4.** *A hybrid cloud composed of an on-premise private cloud and a public cloud.*

*Network Function Virtualization over Cloud-Cloud Computing as Business Continuity Solution DOI: http://dx.doi.org/10.5772/intechopen.97369*

#### *2.4.3 Software-as-a-service (SaaS)*

Within a SaaS context, the consumer can run SaaS provider's applications in a cloud infrastructure. The applications are accessible from various client devices through either a thin client interface, such as a web browser (for example, webbased email), or a program interface. The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings.

In the SaaS model, a provider hosts an application centrally in the cloud and offers it to multiple consumers for use as a service. The consumers do not own or manage any aspect of the cloud infrastructure. In a SaaS context, a given version of an application, with a specific configuration (hardware and software) typically provides services to multiple consumers by partitioning their individual sessions and data. SaaS applications execute in the cloud and usually do not need installation on end-point devices. This enables a consumer to access the application on demand from any location and use it through a web browser on a variety of end-point devices. Some SaaS applications may require a client interface to be locally installed on an endpoint device. Customer Relationship Management (CRM), email, Enterprise Resource Planning (ERP), and office suites are examples of applications delivered through SaaS. **Figure 5** illustrates the three cloud service models.

### *2.4.4 Mobile "backend" as a service (MBaaS)*

In the mobile "backend" as a service (m) model, also known as backend as a service (BaaS), web app and mobile app developers are provided with a way to link their applications to cloud storage and cloud computing services with application programming interfaces (APIs) exposed to their applications and custom software development kits (SDKs). Services include user management, push notifications, integration with social networking services [6] and more. This is a relatively recent model in cloud computing [7] with most BaaS startups dating from 2011 or later [8] but trends indicate that these services are gaining significant mainstream traction with enterprise consumers.

**Figure 5.** *Cloud service models.*
