Data exchanges between diffrent layers

The difference between southbound and northbound plugins is that the southbound plugins talk protocols to network nodes and northbound plugins talk application APIs to the controller applications. As far as the SAL is concerned, there is really no north or south. The SAL is basically a data exchange and adaptation mechanism between plugins. The plugin SAL roles (consumer or producer) are defined with respect to the data being moved around or stored by the SAL. A producer implements an API and provides the data of the API: a consumer uses the API and consumes the data of the API.

While 'northbound' and 'southbound' provide the view of the SAL of a network engineer, 'consumer' and 'producer' provide the view of the SAL of a software engineer, and is shown in the following figure: