e one or more ways to deal with it. Routing Responsibilities So, how are routing decisions made in a typical network? Whether con- nectionless or connection-oriented, the routers and switches in the net- work must take into account a variety of factors to determine the best path for the traffic they manage. These factors fall into a broad category of rule sets called routing protocols. For reference purposes, please refer to the "tree" shown in Figure 2-32. Once the Transport Layer has taken whatever steps are necessary to prepare the packets for their transmission across the network, they are passed to the Network Layer. Figure 2-32 Routing Protocols Routing protocol overview "tree" Dynamic Static Distributed Centralized Non-Isolated Isolated Distance Vector Link State Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Chapter 2 The Network Layer has two primary responsibilities in the name of network integrity: routing and congestion control. Routing is the process of intelligently selecting the most appropriate route through the network for the packets; congestion control is the process that ensures that the packets are minimally delayed (or at least equally delayed) as they make their way from the source to the destination. We will begin with a dis- cussion of routing. Routing Protocols Routing protocols are divided into two main categories-static routing protocols and dynamic routing protocols. Static routing protocols are those that require a network administrator to establish and maintain them. If a routing table change is required, the network administrator must manually make the change. This ensures absolute security, but is labor intensive and therefore less frequently used other than in highly secure environments (e.g. military, health care) or network architectures that are designed around static routing because the routes