1.5 Summary

The OSI reference model is used for building communications systems and networks. Each device implements standard or proprietary protocols for the various layers that it implements. Each layer can be implemented via hardware and/or software. Hosts or end nodes originate and terminate communication, while network nodes like switches and routers transport the corresponding data.

The software implementation for a communications device involves two types of components: protocol software and infrastructure/systems software. Protocol software implements the software as detailed in the specification with higher layer and lower layer interfaces as well as state machines. System software includes the RTOS, drivers, buffer/timer management and other infrastructure functions.