Question: In accordance with Network Domain Security (NDS) Authentication Framework (AF), how should a Network Element (NE) be identified, and what is the signing requirement for its certificate within an operator domain?
Option 1: An NE uses multiple certificates to identify itself, each signed by a different trusted Certificate Authority (CA) outside the operator's domain.
Option 2: An NE uses exactly one certificate to identify itself, which must be directly signed by a CA within the operator domain that the NE belongs to.
Option 3: An NE can choose to use either one or multiple certificates for identification, with the option to be signed by any public CA.
Option 4: Identification is not required through certificates; alternative methods are permissible without direct signing from within the operator's domain.
Explanation: The correct answer reflects the requirement that for Network Domain Security (NDS) and Authentication Framework (AF), each Network Element (NE) must be identified with a single certificate. Moreover, this certificate needs to be directly signed by a Certificate Authority (CA) that is within the same operator domain as the NE. This ensures security, trust, and uniformity across the network elements within an operator's domain, adhering to the specified NDS/AF guidelines.