irtualization. 2 Virtualization and Cloud Computing used as long as the intermediate switches support it. For example, MPLS or GRE tunneling are good choices. Thus, the underlying network only needs to perform routing based on destination address, which is no different than ordinary IP networks. The logical data path is completely implemented in source virtual switch. The source virtual switch usually has multiple tables for the controller to install different logical hops. The destination VM decapsulates the packet and forwards it to the right VM according to the inner packet header. While the design is simple, the main challenges for this design include the data path performance, the ease of management, and the scalability. Managing all pair tunneling itself is a challenging. Because the entire data path is implemented in the source virtual switch, the virtual switch's rule space management is also a key factor to the overall performance. Finally, providing a declarative management interface for the tenants' to flexibly specify their topology and policy is important for its deployment. Wireless Virtualization As a natural extension of wired network virtualization, wireless net- works virtualization is motivated by the observed benefits of that in wired networks. However, while virtualization of wired networks and computing systems has become a trend, much less virtualization has occurred in infrastructure-based wireless networks [33]. Yet, the idea of virtualizing wireless access has recently attracted substantial atten- tion in both academia and industry. It is one of the frontier research areas in computer science [23, 33, 34]. Wireless virtualization may refer to wireless access virtualization, wireless infrastructure virtualization, wireless network virtualization, or even mobile network virtualization [23, 34]. It is about the abstrac- tion and sharing of wireless resources and wireless network devices among multiple users while keeping them isolated. Wireless resources may include low-level PHY resources 