tion of broadcast domains in LANs depends on the physical connection of the devices in the network. Virtual LANs (VLANs) were developed to allow a network manager to logically segment a LAN into different broadcast domains. Thus, VLANs share a same physical LAN infrastructure, but they belong to different broadcast domains. Since it is a logical, rather than a physical, segmentation, it does not require the workstations to be physically located together. They can be on different floors of a building, or even in different buildings. Further, broadcast domain in a VLAN can be defined without using routers; instead, bridging software is used to define which workstations belong to the broadcast domain, and routers are only used to communicate between two VLANs. The sharing and segmentation concept of the VLAN can be gener- alized to a broader set of networks, collectively called (VSNs). The key requirement for such networks is to share a physical infrastructure while being properly segmented [23]. For example, a large corporate may have different networks with specific permission for guests, employees, and administrators, yet all sharing the same access points, switches, router, and servers. 2.3.4 Switch-Based SDN Virtualization Network virtualization enables multiple logical networks to share the same underlying physical network infrastructure in an isolated man- ner. Each logical network can have different addressing and forward- ing schemes. The isolation and abstraction can be implemented at the switch level or the host level. First, we introduce the mechanism of implementing it at the network switch level using SDN. The advantage of this approach is that it does not rely on support from the end hosts. Once deployed, it can be used to support a large number of end hosts simultaneously. It also does not rely on specialized functionalities on the hardware, which then can be deployed on commodity switches. 2 Virtualization and Cloud Computing There are multiple requirements to support network virtualization. Autonom