OSI Reference Model Diagram
(Illustrated Diagram)

Open Systems Interconnection (OSI) is a standard reference model for communication between two end users in a network. It is used in developing products and understanding networks. This figure shows where commonly-used Internet products and services fit within the model. Also see the notes below the figure.

Notes: The OSI Reference Model describes seven layers of related functions that are needed at each end when a message is sent from one party to another party in a network. An existing network product or program can be described in part by where it fits into this layered structure. For example, TCP/IP is usually packaged with other Internet programs as a suite of products that support communication over the Internet. This suite includes the File Transfer Protocol (FTP), Telnet, the Hypertext Transfer Protocol (HTTP), e-mail protocols, and sometimes others. Although TCP fits well into the Transport layer of OSI and IP into the Network layer, the other programs fit rather loosely (but not neatly within a layer) into the Session, Presentation, and Application layers.

In this figure, we include only Internet-related programs in the Network and higher layers. OSI can also be applied to other network environments. A number of boxes under the Application and the Presentation layers do not fit as neatly into these layers as they are shown. A set of communication products that conformed fully to the OSI reference model would fit neatly into each layer.