Question: What types of data can be included in a compressed PDCP SDU within the Data field of a PDCP PDU?
Option 1: Both User Plane and Control Plane data
Option 2: Only Control Plane data
Option 3: Only User Plane data
Option 4: Neither User nor Control Plane data
Explanation: A compressed PDCP SDU (within the Data field) is limited to containing only User Plane data. This distinction is crucial for efficient network operation, as compression is typically more beneficial for the generally larger payloads of user plane data, whereas control plane data, being smaller and more time-sensitive, may not benefit as significantly from compression.