OSI Model

In the early years of networking, sending and receiving data across a network was confusing, because large companies such as IBM, Honeywell, and Digital Equipment Corporation had individual standards for connecting computers. It was unlikely that applications operating on different equipment from different vendors could communicate. Vendors, users, and standards bodies needed to agree upon and implement a standard architecture that would allow computer systems to exchange information even though they were using software and equipment from different vendors.

In 1978, the International Standards Organization (ISO) introduced a networking model, called the Open Systems Interconnection (OSI) model, as a first step toward standardizing data communications standards to promote multi-vendor network interoperability.

The OSI model consists of layers, each with a specific set of network functions. The model specifies the set of protocols and interfaces to implement at each layer and provides guidelines for implementation of the interfaces between layers.

In This Appendix

OSI Layers

Data Flow in the OSI Model

Vertical Interface Terminology in the OSI Model