Virtualization in Software - Defined Networks

H osted cloud computing has signif icantly lowered the barrier for creating new networked services. Likewise, experimental facilities such as the Global Environment for Network Innovations (GENI; www. geni.net) let researchers perform largescale experiments on a “slice” of shared infrastructure. By letting tenants share physical resources, virtualization is a key technology in these infrastructures. Although virtual machines are now the standard abstraction for sharing computing resources, the right abstraction for networks is a subject of ongoing debate. Existing solutions differ in the level of detail they expose to individual tenants. Amazon Elastic Compute Cloud (EC2) offers a simple abstraction in which all of a tenant’s virtual machines can reach each other. Nicira extends this “one big switch” model by offering programmatic control at the network edge to enable, for example, improved access control (see http://nicira.com/ en/network-virtualization-platform). Oktopus exposes a network topology so tenants can perform customized routing and access control based on knowledge about their own applications and traffic patterns.1 Each abstraction is most appropriate for a different class of tenants. As more companies move to the cloud, providers must go beyond network bandwidth sharing to support a wider range of abstractions. With a flexible Network virtualization gives each “tenant” in a data center its own network