What is l3 in 5G?

The 5G layer-1 is PHYSICAL Layer. The 5G layer-2 include MAC, RLC and PDCP . The 5G layer-3 is RRC layer as shown in 5G protocol stack. The Figure-1 depicts 5G Protocol Stack consisting of both User Plane and Control Plane protocol layers.

5G Toolbox and the 5G NR Protocol Layers

5G-NR Layer 3 (RRC) Functions: Establishment, maintenance, and release of an RRC connection between the UE and NG-RAN including Addition, modification, and release of carrier aggregation, Addition, modification, and release of Dual Connectivity in NR or between E-UTRA and NR.4 Eyl 2017