Protocol stack: RRC, SDAP, PDCP, RLC, MAC, PHY

Six Layers from Air to Application

The NR radio protocol stack comprises six layers stacked from the physical interface up to connection management. At the top, RRC manages connection establishment, handover decisions, and measurement configuration for mobility. Immediately below sits SDAP, the only protocol layer new to NR, responsible for mapping 5GC QoS flows onto data radio bearers. PDCP provides ciphering, integrity protection, robust header compression, packet reordering, and duplicate detection across split bearers. Together these three upper layers run on the CU, separated from the time-critical lower layers.