Hi
in case of MPLS, you also sometimes need overhead based on security and routing for direct-to-direct communication (spoke-to-spoke lets say).
In SD-WAN, you may define different VRF for VOIP or filter non-VOIP subnets and let go to Hub if it is not VOIP network, define simplified control/ data policy for site. But in any case BFD sessions between routers are needed.
Question: how many branches do you have?
HTH,
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