An SD-WAN is managed across existing Internet and MPLS VPN WANs between two sites. This use case enables the subscriber to use an encrypted SD-WAN tunnel over the Internet to augment their site-to-site MPLS VPN bandwidth and achieve higher resiliency using two WANs. 

This use case illustrates the different LSO RA interfaces between the different SD-WAN service components. Both sites are using an SD-WAN Edge CPE. The CSP or MSP delivers the SD-WAN service over existing Internet and MPLS VPNs which may be provided by a different CSP or MSP. 

This is perhaps one of the most popular use cases because many enterprise subscribers have both Internet and MPLS WANs to interconnect their sites so the SD-WAN managed service enables them to take advantage of the benefits that SD-WAN provides over multiple WAN connections.