Question: What is the requirement for a transmitter compliant with the current version of the 3GPP RRC protocol specification regarding the setting of spare bits and the extension part of a PDU (Protocol Data Unit)?
Option 1: Set spare bits to one and the extension part to non-empty, unless explicitly indicated otherwise on a PDU type basis.
Option 2: Set spare bits to zero and the extension part empty, unless explicitly indicated otherwise on a PDU type basis for transmitters of later versions.
Option 3: Choose either zero or one for spare bits, and set the extension part based on transmitter version without specific guidelines.
Option 4: Ignore spare bits but set the extension part according to the transmitter's compliance version.
Explanation: A transmitter compliant with the current specification must set spare bits to zero for compatibility and set the extension part empty, unless otherwise indicated for certain PDU types, to prevent backwards compatibility issues with later-version transmitters.