Cloud computing has become a signi cant technology trend. With the cloud computing technology, users use a variety of devices to access programs, storage, and application- development platforms over the Internet, via services offered by cloud computing providers. Advantages of the cloud computing technology include cost savings and high availability. Access to the infrastructure in Cloud Computing incurs payments. To design and develop Cloud technologies focus on defining novel methods, policies and mechanisms for efficiently managing Cloud infrastructures. To test these newly developed methods and policies, researchers need tools that allow them to evaluate the hypothesis prior to real deployment in an environment where one can reproduce tests free of cost. Simulation- based approaches offer significant benefits. CloudSim enables seamless modeling, simulation, and experimentation of emerging Cloud computing infrastructures and application services. In the CloudSim simulator there are two problems: Lack of links between Datacenters and no possibility to create a virtual machine (VM) in more Datacenters. In this paper we propose a ring topology to allow the exchange and the sharing of information and services between different Datacenter, and we improve the method of creating VMs to allow the creation of VMs in several Datacenter, which improves fault tolerance in this type of environment.