The document provides an overview of the OSI model, which is a standard communication architecture for connecting devices. It describes the seven layers of the OSI model from physical to application layer and their functions. Each layer provides services to the layer above it and communicates with the same layer on other systems. Data is encapsulated with protocol information as it moves down the layers before being transmitted over the network.

6. OSI Reference Model: 7 Layers OSI Model

17. OSI & TCP/IP Models TCP/IP Model

18. TCP/IP Model TCP/IP Model Application Layer Application programs using the network Transport Layer (TCP/UDP) Management of end-to-end message transmission, error detection and error correction Network Layer (IP) Handling of datagrams : routing and congestion Data Link Layer Management of cost effective and reliable data delivery, access to physical networks Physical Layer Physical Media