Question: Which of the following protocols is NOT used for header compression/decompression by the PDCP layer, as per its supported functions?
Option 1: ROHC (Robust Header Compression) protocol
Option 2: EHC (Enhanced Header Compression) protocol
Option 3: UDC (Uplink Data Compression) protocol
Option 4: IPComp (IP Payload Compression) protocol
Explanation: According to the PDCP layer's functions, ROHC and EHC are used for header compression/decompression. UDC is used for uplink data compression/decompression, not header compression/decompression, making it the correct answer due to its different application.