Cloud computing is an IT concept that offers cloud services from one or more service providers on distributed resources. Cloud services are hierarchically divided into three levels: The infrastructure level for hardware, the platform level for software development and the application level.
The lowest level comprises the infrastructure. This level is about hardware, computing capacities, storage space and the communication links with the underlying network infrastructure. The cloud services available are Infrastructure-as-a-Service( IaaS), Storage-as-a-Service( SaaS) and Communication-as-a-Service( CaaS).
The layer above is about the middleware with the software development components for the system integrators. At this level are the cloud services Platform-as-a-Service( PaaS) and Software Infrastructure-as-a-Service( SIaaS). And the upper level is about business applications, unified communications as a service( UCaaS), software as a service (SaaS), business as a service( BaaS), mobile backend as a service ( MBaaS), video as a service ( VaaS), document management and compliance. Applications at this level tend to be standardized, with few options for integration or customization into non- standard solutions. However, there are numerous services that can be offered as a service. In this context, we speak of Anything-as-a-Service(XaaS).
The complete range of cloud services is rounded off by the security and management aspects: Firewall-as-a-Service( FWaaS), Security-as-a-Service (SaaS), Encryption-as-a-Service( EaaS) and Monitoring-as-a-Service( MaaS).