The QOS Tools

As with any technology, as QOS matures and evolves, new developments always occur and features are always being added. However, before diving deeply into the specifics and all possible variations and evolutions of each QOS tool, the first step is to understand the basic structure of each tool. This chapter presents a high-level view of the fundamental QOS tools. The complexities and specifics of these tools are explained in Part Two of this book.

In a general sense, a QOS tool is simply a building block. It receives input, processes it, and produces specific output. The relationship between the input and output depends on the internal mechanisms of the QOS tools.

Examining each QOS building block separately, focusing on the results each one delivers, allows us to determine how to combine them to achieve the desired behavior.

To explain the QOS building blocks, this chapter focuses on a single router that is part of a network in which QOS is implemented. The router has an ingress interface on which traffic arrives at the router, and an egress interface from which traffic departs the router. It is between these two interfaces that QOS tools are applied to the traffic.

2.1 Classifiers and Classes of Service

Classifiers perform a task that is somewhat analogous to an “identification” process. They inspect the incoming traffic, identify it, and then decide to which class of service it belongs.

The basis of QOS is traffic differentiation, and the concept of a class of ...

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