Introduction

Routing is a critical function in the global switched telephone network.

The routing architecture in the switched telephone network is based on the notion of hierarchical routing that was originally designed a half a century ago, and the hierarchical concept as it was thought of is still in place in the overall global switched telephone network architecture. In addition, dynamic call routing schemes have been introduced in the past 25 years that can function in this hierarchical architecture.

In this chapter, we will present both hierarchical routing and dynamic routing.

The reader might want to note that the term dynamic routing used in this chapter refers to dynamic call routing in the telephone network; it should not be confused with dynamic routing in IP networks.

It is possible to have routing functionalities in a network without introducing loops even in the absence of any information exchange as long as nodes are labelled differently; this is the case with hierarchical routing; in a sense, this is a remarkable achievement. Most dynamic call routing schemes for the telephone network require exchange of link state information—such information exchange does not use flooding; instead separate dedicated channels or a signaling network are used.

Introduction

The route computation is primarily based on bandwidth availability while the exact computation is different for different routing.

There is, however, at least one Dynamic Routing Scheme (DAR) that does not require any information exchange to do route computation. While routing can address certain congestion issues in a network, it cannot by itself take care of all types of congestion; rather, a good network requires proper control schemes in addition to routing schemes for efficient workings.