由于flowvisor只有4个版本， 最新更新都是2013年的， 跟底层ovs版本不跟进， 最近斯坦福post一个 ovx， 猜测是flowvisor的加强版， 所以看一下文档说明
文档详见http://ovx.onlab.us/about/
OpenVirteX is a network virtualization platform which allows you to specify your own topology and addressing while retaining control of your virtual OpenFlow network. In essence, we are introducing the concept of programmable virtual networks.
ovx是一个网络虚拟化平台， 允许指定拓扑与寻址，同时可以控制底层基于openflow的网络。
ovx位于上层虚拟网络控制器与底层网络设备之间，具有以下功能：
1 创建指定的虚拟网络拓扑
2 使用自己的网络操作系统
3 可以使用整个地址空间
4 可以随意在运行时，更改虚拟网络，自动从物理失效中恢复
http://ovx.onlab.us/documentation/faq/
这里讲述了ovx的相关问题
我们看一下ovx与flowvisor的区别与相同点：
相同：都是基于openflow1.*版本，都是提供网络虚拟化
不同点：目前没看懂~~~好忧桑 还有神马怎么隔离的 等我研究一下
flowvisor直接根据节点信息建立流表，进行转发流表，顺便带宽隔离， 但是ovx更接近VNE，有做VNE的组件，只要存储节点的MAC地址，有利于部件损坏后的迁移
The best way to understand this is to see what both do to the packet header space (flowspace).
In short, OpenVirteX gives you a full packet header space (a virtual copy for your own virtual network), whereas FlowVisor lets you divide up a single packet header space into subsets to assign to your slices.
So, if you want whole new virtual networks, use OpenVirteX, and if you just want to group hosts based on specific header field values (IP addresses, TCP/UDP port values, etc), use FlowVisor
While similar in the ability to allow multiple tenants to coexist, this differs from network slicing, which splits up portions of a single header space amongst all of the tenants. For example, two tenants in their own virtual networks can use the same IP subnets and TCP/UDP ports, while in two slices, this will cause traffic to leak between the slices. Another difference is in possible topologies – virtual networks need not correspond to the topology of the underlying network, while a slice is restricted to an isomorphic subgraph.
放弃flowvisor， 投入ovx的怀抱