Question: In the 3GPP Network Domain Security (NDS) Authentication Framework (AF) PKI architecture, how are trust relationships typically established between different security domains?
Option 1: Through a centralized Trust Anchor shared among all domains
Option 2: Using direct cross-certifications between the security domains
Option 3: Relying on a hierarchical structure with subordinate CAs for each domain
Option 4: Employing a third-party Trusted Service Manager (TSM) for brokerage
Explanation: The correct answer reflects the approach in the NDS/AF PKI architecture, utilizing direct cross-certifications between security domains. This facilitates straightforward policy configurations within Security Gateways and TLS entities, enhancing interoperability and simplicity.