In addition, virtual networks (VNs) can share the resources in the physical substrate. Network virtualization enables the deployment of novel network architectures and services on existing Internet infrastructure. Experimental results demonstrate that FVM is more flexible and scalable, requires less system resource, incurs lower start-up and run-time performance overhead than existing hardware-level virtual machine technologies, and thus makes a compelling build- ing block for security and fault-tolerant applications. A main techni- cal challenge in FVM is how to achieve strong isolation among different virtual machines and the host machine, due to numerous namespaces and interprocess communication mechanisms on Win- dows. Through a copy-on-write scheme, FVM allows multiple virtual machines to physically share resources but logically isolate their resources from each other. The key technique behind FVM is namespace virtualiza- tion, which isolates virtual machines by renaming resources at the OS system call interface. In this paper, we intro- duce an OS level virtual machine architecture for Windows applica- tions called Feather-weight Virtual Machine (FVM), under which virtual machines share as many resources of the host machine as possible while still isolated from one another and from the host machine. Virtual machine technology meets this requirement perfectly because it provides an execution envi- ronment that is both realistic and isolated. Many fault-tolerant and intrusion-tolerant systems require the abil- ity to execute unsafe programs in a realistic environment with- out leaving permanent damages.
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