The document discusses the 7 layers of the OSI model: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has a specific function and protocol data unit (PDU). The Physical layer deals with physical components like cables. The Data Link layer handles framing and MAC addressing. The Network layer deals with IP addressing and routing between devices. The Transport layer focuses on reliability and flow control of data segments. Above this are the Session, Presentation and Application layers which handle user sessions, data translation and different application protocols.