1.4 Design Considerations-A Prelude

• The following is an example of some of the issues faced by designers and developers of communications software. It is important that these issues are addressed early in the design for the product to meet its requirements.

• Does the hardware architecture involve one processor or multiple processors? Partitioning of functions will depend upon the number of processors.

• Has the RTOS been chosen? If so, does it provide memory protection between processes/tasks? The task partitioning and interfacing will depend upon this.

• What kind of performance is required? Can this be implemented completely in software, or does it require some hardware acceleration support?

• What are the protocols to be implemented, and how do they interface with the system software and other protocols? Can any of the protocols be accelerated via hardware?

• What kind of global data structures and tables are to be used for the implementation?

• What kinds of buffer and timer management are required?

• What kind of error notification and handling are required? Does the software require extensive configuration and control? What are the types of interfaces to be provided for such management?

• Does the RTOS provide a simulator which can be used for the development while the hardware is getting ready? What kind of testing can be done with the simulator? What kind of testing can be performed once the hardware is ready?

This book addresses these issues using the Layer 2/3 switch (or router) as an illustrative example. The aim is to provide the reader a flavor of the design considerations and tradeoffs in building communications software.