After you have designed and built your internetwork, there is no time to rest on your laurels. The priority must now shift to maintaining acceptable levels of performance across the internetwork. This requires the collection, and continuous monitoring, of performance metrics.
Many different criteria, or metrics, can be applied to measuring the performance of an existing WAN. Many of these are fairly objective and can be automatically extracted from the network monitoring protocols native to virtually every network device. Others are subjective and can be next to impossible to determine in advance.
Some of the most common metrics are the following:
Resource utilization rates