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which are private clouds using online virtual private networks to
provide a secure connection with this private cloud
environment.

C. The back end

As mentioned earlier, the backend represents the cloud itself,
which in turn consists of 6 layers:

(1) The physical layer:

The core component of the cloud is the physical infrastructure
of hardware, servers, CPUs, storage devices, network
communication devices and other network-related and storage
devices. Here, it should be noted that this physical network
infrastructure has a heterogeneous nature, and based on the
idea of cloud computing, it does not exist in one place, but it is
distributed in different geographical places.

(2) The virtualization layer:

It is theoretically responsible for taking all heterogeneous
devices and their physical distribution into account to create a
single, and logical view of the entire physical layer that makes
up the cloud. In practice, such a representation is done through
a program known as a virtual machine monitor (VMM) or
hypervisor. The aim of this program is to combine all the physical
devices, form a comprehensive and logical representation of
these resources, and make them available to users according to
their requests.

(3) Cloud services layer:

Here are the types of services provided by cloud service
providers which are mainly three types: Infrastructure as a
service (IaaS), Platform as a service (PaaS), and Software as a
service (SaaS).

(4) Scheduling, provisioning, and pricing layer:

This layer is concerned with the management and coordination
services for the cloud environment. These are basic services

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