9.2 OPEN SYSTEMS

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Open Systems Principles

Entity is a group of functions for a particular task. Accept input, and produce output.

Layer is a group of functions designed to provide a set of services related to the mission of that layer

Entities provide a set of services to the layer above. In doing this they use the services of the underlying layers.

Each layer isolates the layer above from the details of the underlying layers, and thus a lower layers characteristics can change without affecting the rest of the system.

Primitives control the layer's services and data flow. Primitives fall into 4 groups: Request, Indicate, Response, and Confirm

We can do a simple comparison of networking models