Broadcast: Periodic MIB/SIB (e.g., cell ID, PLMN).
Paging: UE notification in IDLE/INACTIVE (e.g., incoming call).
ETWS/CMAS: Emergency alerts (e.g., tsunami warning).
Dedicated signalling: RRC messages for a specific UE (e.g., RRCReconfiguration).
Positioning assistance: Assistance data for location (e.g., OTDOA).
App layer measurement: UE collects app‑layer data (e.g., QoE).
Integrity protection: Prevents tampering of RRC/NAS messages.
Ciphering: Encryption of user/data plane.
Loss‑less in‑sequence: PDCP reordering & retransmission.