364 Routing in Data Networks Chap.5 cope with link and node failures,requiring redirection of traffic and an update of the databases maintained by the system.Third,to achieve high performance,the routing algorithm may need to modify its routes when some areas within the network become congested. The main emphasis will be on two aspects of the routing problem.The first has to do with selecting routes to achieve high performance.In Sections 5.2.3 to 5.2.5, we discuss algorithms based on shortest paths that are commonly used in practice.In Sections 5.5,5.6,and 5.7 we describe sophisticated routing algorithms that try to achieve near optimal performance.The second aspect of routing that we will emphasize is broadcasting routing-related information (including link and node failures and repairs) to all network nodes.This issue and the subtleties associated with it are examined in Section 5.3. The introductory sections set the stage for the main development.The remainder of this section explains in nonmathematical terms the main objectives in the routing problem and provides an overview of current routing practice.Sections 5.2.1 to 5.2.3 present some of the main notions and results of graph theory,principally in connection with shortest paths and minimum weight spanning trees.Section 5.4 uses the material on graph theory to describe methods for topological design of networks.Finally,Section 5.8 reviews the routing system of the Codex network and its relation to the optimal routing algorithm of Section 5.7. 回+@回回回回 Packet from user n 回②+回+ 2 3 3 Figure 5.1 Routing in a datagram network.Two packets of the same user pair can travel along different routes.A routing decision is required for each individual packet.364 Routing in Data Networks Chap. 5 cope with link and node failures, requiring redirection of traffic and an update of the databases maintained by the system. Third, to achieve high performance, the routing algorithm may need to modify its routes when some areas within the network become congested. The main emphasis will be on two aspects of the routing problem. The first has to do with selecting routes to achieve high performance. In Sections 5.2.3 to 5.2.5, we discuss algorithms based on shortest paths that are commonly used in practice. In Sections 5.5, 5.6, and 5.7 we describe sophisticated routing algorithms that try to achieve near optimal performance. The second aspect of routing that we will emphasize is broadcasting routing-related information (including link and node failures and repairs) to all network nodes. This issue and the subtleties associated with it are examined in Section 5.3. The introductory sections set the stage for the main development. The remainder of this section explains in nonmathematical terms the main objectives in the routing problem and provides an overview of current routing practice. Sections 5.2.1 to 5.2.3 present some of the main notions and results of graph theory, principally in connection with shortest paths and minimum weight spanning trees. Section 5.4 uses the material on graph theory to describe methods for topological design of networks. Finally, Section 5.8 reviews the routing system of the Codex network and its relation to the optimal routing algorithm of Section 5.7. B-- Packet from user n Figure 5.1 Routing in a datagram network. Two packets of the same user pair can travel along different routes. A routing decision is required for each individual packet