3.4 Developing Service Metrics

After gathering requirements for the network, the next step is to analyze these requirements so that you can distinguish between various performance levels in the network. We will develop and use performance thresholds and limits to distinguish between low and high performance and will also use performance characteristics to identify predictable and guaranteed performance levels. Performance thresholds, limits, and characteristics are measured in the system with service metrics.

Service metrics either are actual measurable quantities in the network or are derived from measured quantities. These service metrics are important; they are where "the rubber meets the road" where requirements from all layers in the system are distilled into configurable and measurable quantities.

Recall from Chapter 2 that for a performance characteristic to be useful, it must be configurable, measurable, and verifiable within the network. This is particularly true when parts of the network are outside the control of the network administrator, for example, when a service provider is contracted to supply a service such as ATM or frame relay in the network or when parts of the network (or the entire network) are outsourced. In such cases, service metrics can be used to ensure that you are getting the service you are requesting (and paying for) from the service provider or outsourcing agent.

The types of service metrics you will use will depend on your design and the types of equipment (network devices) you implement in the network, but at this point in the analysis process,...