Question: For a User Equipment (UE) that supports S1-U data transfer or User plane CIoT EPS Optimisation, what does the `maxNumberROHC-ContextSessions-r13` field specifically define, in relation to header compression?
Option 1: The minimum number of uncompressed header context sessions required for UE operation.
Option 2: The maximum number of header compression context sessions supported by the UE, excluding those leaving all headers uncompressed.
Option 3: The total number of header compression and non-compression context sessions a UE can handle simultaneously.
Option 4: The threshold for switching between compressed and uncompressed header modes based on session load.
Explanation: This is correct because the `maxNumberROHC-ContextSessions-r13` field is defined to specify the upper limit of header compression context sessions that a UE can support, with the explicit exclusion of sessions where no headers are compressed. This directly relates to managing and optimizing data transfer (e.g., S1-U) and specific optimizations like CIoT EPS, ensuring efficient use of resources for supported UEs, especially those categorized under `ue-Category-NB`.