OSI Reference Model

OSI is an abreviation of Open System Interconnection.
It has got a seven layer architecture.
Layer 1: Physical Layer
It defines the physical, mechanical and electrical charecteristics such as voltage, current, transmission distance, physical connectors etc.
Layer 2: Data Link Layer
Data Link Layer is devided into two. LLC(Logical Link Control), MAC(Mediam Access Control)
Layer 3: Network Layer
Routing related informations
Layer 4: Transport Layer

Layer 5: Session Layer
Layer 6: Presentation Layer
Layer 7: Application Layer