This document provides an overview of the OSI reference model, which is an internationally standardized architecture for how network communication should work. It describes the seven layers of the OSI model from the physical layer up to the application layer. Each layer provides services to the layer above it and receives services from the layer below. The layers relate to either communication technologies (layers 1-4) or user applications (layers 5-7). The document also discusses how the OSI model differs from Internet protocols and covers concepts like connection types, reliability, and the relationship between services and protocols.