Installation guide

Network Infrastructure for EtherNet/IP™
B-1
Appendix B Overview of the OSI Model, EtherNet/IP and CIP
Appendix B Overview of the OSI Model, EtherNet/IP
and CIP
The Open System Interconnection (OSI) Reference Model describes how information from a
software application in one computer moves through a network medium to a software application in
another computer. The OSI Reference Model is a conceptual model composed of seven layers, each
specifying particular network functions as shown in Figure B-1. The International Organization for
Standardization (ISO) developed the model in 1984, which is now considered the primary architectural
model for inter-computer communications.
The OSI Model divides the tasks involved in moving information between networked computers into
seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the
seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be
implemented independently. This enables the solutions offered by one layer to be updated without
adversely affecting the other layers.
Figure B-1 The OSI Reference Model’s Seven Independent Layers.
Characteristics of the OSI Layers
The seven layers of the OSI Reference Model can be divided into two categories: upper layers and lower
layers as shown in Figure B-2.
Figure B-2 The OSI Model’s Two Sets of Layers.