Each virtual network in a network virtualization environment is a set of virtual nodes and virtual links. Essentially, a virtual network is a subset of underlying physical network resources. Network virtualization provides a decoupling of functionality in a network environment by separating the role of traditional ISPs between InPs (infrastructure providers) who manage the physical infrastructure and SPs (service providers) who create virtual networks by aggregating the resources of several InPs and offer end-to-end services. end network services. In order to create networks compatible with a virtual network, the following specifications must be met. Robustness: the network must continue to function in the event of a node or link failure. Manageability: The InP must have a view of the underlying physical topology, status, and other parameters associated with the equipment providing the virtual network. Network Traffic and Resource Control: Traffic engineering and management techniques performed by the InP must not restrict the basic operation of a virtual network. Isolation: Isolation mechanisms between virtual networks must be provided. It must be ensured that malfunctions of virtual networks do not affect the performance of other virtual networks sharing the same resources. Scalability: Any technical solution must be scalable to accommodate an unlimited number of virtual networks. On-demand provisioning: It must be possible to create, modify, and delete virtual networks dynamically on demand. In general, a virtual network will have a limited lifetime.6.2 Virtual Network ID, Virtual Link ID: In order to control virtual networks spanning multiple infrastructure domains, virtual networks must be identified by a virtual network ID. Addit...... middle of article...... Conference, vol.2 1998.[6] Rob Sherwood, Glen Gibb- “Flow visor: A network virtualization layer” OPENFLOW- TR-2009-1.[7] White Paper - “Network Functions Virtualization” from October 22 to 24, 2012 during the “SDN and Openflow World Congress”, extracted from portal.etsi.org/nfv/nfv_white_paper.pdf.[8] “Network Virtualization - The New Building Blocks of Network Design” – Cisco White Paper http://www.cisco.com/c/en/us/solutions/enterprise-networks/network-virtualization-solutions/white- paper-listing. html[9] Aun Haider, Richard Potter, Akihiro Nakao- “Challenges in Resource Allocation in Network Virtualization”- at the 20th ITC Seminar, 18-20, May 2009.[10] Gregor Schaffrath, Anja Feldmann, Mario Kind, “Network virtualization architecture: proposal and initial prototype”, August 2009.[11] Frank Yue- “Network Functions Virtualization – Everything Old is New Again”, f5 networks