The 3DS Method link runs in a hidden iframe that the 3DS Server loads in the checkout page so the ACS can load JavaScript that gathers device information tied to the 3DS Server Transaction ID; it uses a URL distinct from the challenge URL, a separate TLS link with server authentication of the ACS, and a commercial CA certificate. Links e, f and g (integrator to acquirer, acquirer to payment system, payment system to issuer) are the regular payment links with no additional 3DS requirement.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.