NaaS Oam

      When the customers use openstack neutron to create their virtual networks, they need to know the health status of their virtual networks at running time. So it is necessary to support the mechanism of oam for virtual network. So the customers may periodly use the oam mechanism to check their VN's health status. Or, the Applications/services may use the oam mechanism to detect the SLA of endpoint to endpoint's path on-demand. According the network/path information(qos/delay/jitter/bandwidth/priority/and so on), the applications/services can adjust their policys to fit the network well. or troubleshooting the fault node/link.