L 1-7 (Layer 1-7)
The OSI (Open System Interconnection) model defines a networking framework to implement protocols in seven layers (Ls). Layer 1 (L1) is the physical layer that conveys the bit stream through the network at the electrical and mechanical level. Layer 2 (L2) is the data link layer, where data packets are encoded and decoded into bits. Layer 3 (L3) is the network layer, which provides switching and routing technologies. Layer 4 (L4) is the transport layer, which provides transparant transfer of data between end systems. Layer 5 (L5) is the session layer, which establishes, manages and terminates connections between applications.