Question: Which CA is responsible for issuing certificates to Network Elements (NEs) for communication within the same security domain over the Zb-interface?
Option 1: TLS Client CA
Option 2: Interconnection CA
Option 3: SEG CA of the domain's subordinate CA (implied as 'An issues certificates to NE's')
Option 4: TLS Server CA
Explanation: The correct answer is implied within the structure of telecom security domains. For NEs communicating within the domain (Zb-interface), a subordinate or another CA associated with the domain's structure, likely under the SEG CA's hierarchy or a similar domain-specific authority, issues certificates. This aligns with Option 3's implication of a domain-specific CA responsible for NE certificates within that domain.