Question: What is the nature of Sidelink Relay UE operation support in User Equipment (UE) as per E-UTRA specifications?
Option 1: Mandatory for all UEs to ensure seamless relay functionality.
Option 2: Conditional, based on the specific frequency band used by the UE.
Option 3: Optional, as specified in the Radio Resource Control (RRC) protocol specification.
Option 4: Dependent on the UE's capability to support a minimum of two simultaneous radio links.
Explanation: The correct answer is Option 3 because, according to E-UTRA specifications, particularly those related to Radio Resource Control (RRC) protocol, supporting sidelink relay UE operation is not obligatory for all User Equipment. This means manufacturers have the flexibility to choose whether to include this feature in their UEs, making it an optional capability. This aligns with efficient resource allocation and tailored functionality based on anticipated use cases or market requirements.