A VMware node can backup and restore Virtual Disks belonging to VMs or Templates using different VMware ‘Transport Modes’. The method(s) chosen for any job will depend on the system and network configurations. The choice of which to use is made by the VMware VADP VDDK library, which will first check to see whether the most efficient transport mode can be used, then backing off through the modes to the least efficient. Protector has no influence on this decision, but, if required, transport modes can be excluded.
Refer VMware's Virtual Disk Transport Methods topic available at https://developer.vmware.com/docs/16967/virtual-disk-development-kit-programming-guide/GUID-15395099-5300-4D3F-BCC3-E50DCDC954C2.html