13.2 Performance Engineering – Requirements, Targets, and Achievables

Here, performance requirements are taken to mean desired or specified performance objectives, as in Figure 13.4:

Figure 13.4: Performance requirements and achievables

The highest-level specifications, project performance requirements, are generated by the needs of the system itself. These, together with functional and other requirements, act as inputs to the system design activity. In developing system architectures to meet these needs, designers (even at this early stage) usually try to define what actually can be achieved. Take, for example, where the architectural model consists of two computers linked by a dedicated serial data link. Assume that the following items have been decided on:

• Link protocol: HDLC
• Transmission rate: 1 Megabit/sec
• Message length (minimum): 32 bytes
• Protocol overhead: 6 bytes

Elementary calculations show that it will take at least...