Efficiency is a nebulous term. In general, it measures how thoroughly one manages to achieve some desired result as a function of the required resources. The biggest problems in implementing efficiency in a computer network are essentially matters of definition. What is the desired result for a network, and what resources are actually required?
With a relatively narrow view of the desired results in network design, it essentially comes down to the factors that I mentioned earlier when talking about network reliability. The network must deliver data to the destination. It must do so within the required application constraints. In most networks, the desired result is effectively quantified with just four parameters: latency, jitter, throughput, and dropped packets. I will define these terms when I come to talk about Quality of Service later in this chapter.
The hard part of describing efficiency is actually in defining the resources. Which resources should the definition include? Some resources are obvious. Everybody would agree that it's necessary to worry about CPU and memory utilization in their routers. The same is true for the bandwidth utilization on the various links that connect network devices. But some resources are harder to quantify or harder to see. How do you compare the relative importance of these resources? Do you want to save bandwidth, for example, at the expense of CPU load?
The ultimate resource for any organization comes down ...