An accurate assessment of the requirements for continuous service at full performance level must be included in the requirements analysis process, along with a statement of specific, measurable requirements. During the architecture and design processes, tradeoffs must take into account the impact of supportability, and the concept of operations must be formulated. Last, during implementation, two major tasks must be accomplished to ensure supportability: 1. Conformance to the network architecture and design must be validated and nonconformance corrected or (at least) documented to ensure that performance is adequate and that maintenance can be performed. 2. Operations and maintenance personnel must understand and be trained in the technologies that are being deployed, including how to operate the network and system properly, when to perform maintenance, and how to most quickly restore service in the event of a fault. A detailed discussion of how supportability fits into the overall architecture and design processes is provided in Chapter 2. 1.11 Conclusion In this chapter you learned definitions of network analysis, architecture, and design; the importance of network analysis in understanding the system and providing a defensible architecture and design; and the model for the network analysis, architecture, and design processes. You have also learned that networks are not independent entities but rather a part of the system and that the delivery of network services is a goal of the system. Network services consist of performance and function and are offered to users, 54 CHAPTER 1 Introduction applications, and devices so that they can accomplish their work on the system. In order to architect and design a network to support services, you need to know what they are, how they work together, and how to characterize them. Once you do this, you will have a broad view of what the network will need to support, which you can take to the next levels of detail as you proceed with the network analysis. By describing the system as a set of components (e.g., user, application, device, network), you can apply interfaces between these components to help understand the relationships, inputs, and outputs between each of the components. You have also learned about different types of services, from besteffort, unpredictable, and unreliable service to predictable, bounded, and somewhat predictable service, to guaranteed services with accountability. To go to a level deeper in the discussion about services, we considered the service performance characteristics capacity, delay, and RMA (reliability, maintainability, and availability). These characteristics are useful only if we can measure and verify their values in the system. We discussed these values, as well as service metrics, thresholds, and boundaries. We learned that performance characteristics can be combined into a performance envelope.