Chapter 4: Flow Analysis

The results of requirements analysis—the requirements specification and requirements map—list and describe requirements that have been gathered and derived for a network. Many of these will be performance requirements (capacity, delay, and reliability, maintainability, and availability [RMA]) for users, their applications, and devices. Such performance requirements, along with the locations of users, applications, and devices from the requirements map, form the basis for estimating where traffic will flow through the network. Flow analysis is the process of characterizing traffic flows for a network, where they are likely to occur and what levels of performance they will require.

The intent of flow analysis is not to show every possible flow in a network but rather to show those flows that will have the greatest impact on the network architecture and design. This is often a small fraction of the total set of flows for a network.

4.1 Objectives

In this chapter, you will learn how to identify and characterize traffic flows. We will discuss individual, composite, and critical flows and how to determine when each applies. You will learn mechanisms to help identify and characterize flows, including data sources and sinks and flow models. Finally, you will learn about flow specifications, where performance requirements are combined for a flow or group of flows. Flow specifications are used as input to the network architecture and design processes, covered later in this book.