OSI Protocols - Overview

Overview

OSI protocols stacks are split into seven layers. The layers form a hierarchy of functionality starting with the physical hardware components to the user interfaces at the software application level. Each layer receives information from the layer above, processes it and passes it down to the next layer. Each layer adds its own encapsulation information (header) to the incoming information before it is passed to the lower layer. Headers generally include address of destination and source, check sums (for error control), type of protocol used in the current layer, and other options such as flow control options and sequence numbers (used to ensure data is sent in order).

The Manufacturing Automation Protocol (MAP) user group, focused on real-time control of manufacturing robots of various types, implements layer 1 (physical), a two-sublayer layer 2 (data link) with LLC Type 3 on top of the medium access layer, and then the layer 7 Manufacturing Message System on top. Layers 3 to 6 are not present. This stack is intended just for the robots themselves; the robot controller would load files with a full seven-layer stack with FTAM file transfer on top. Parts of the Signaling System 7 stack are OSI derivatives.