2. A model for a WAN design

In this section, a model for the design of a WAN is introduced. The model tries to show the most essential aspects which are considered when designing access and backbone networks. In this model, some parameters are not considered: the operation probability of the lines and equipment, the number of equipment ports, and the memory capacity of the equipment. The objective is to design a WAN with the smallest possible installation cost, so that the constraints are satisfied.

In what follows, the data of the model are presented as well as its formalization as a combinatorial optimization problem on weighted graphs. The goal is to find the optimal topology that satisfies the imposed constraints to the access and backbone networks. Figure 1 shows an example of a wide area network. The information available for each type of equipment (switch and concentrator) and each type of connection line, as well as the line laying, is the following:

	- ce is the cost by kilometer of the line type e. Here the laying cost is not included.
	- ve is the speed in Kbits/s of the line type e.

Figure 1. WAN example.

	- cw is the installation cost of the switcher type w.
	- vw is the speed in Kbits/s of the switcher type w.

In terms of graph theory, a model for the design of a WAN, based on the problem, is presented as follows. Some notation is introduced next, that is then used to formally define the problem.


Definition 1 (WANDP—wide area network design problem). Let G ¼ ðS; EÞ be the graph of feasible connections on the WAN. The wide area network design problem ðS; E;K;W; Ea;C; DST ;VST Þ consists in finding a subnetwork of G of minimum cost which satisfies the following points:

1. The backbone network topology must be at least 2-node-connected.

2. The access and backbone networks must be able to support the demand of connection and traffic required by the terminal sites.

Given the complexity of the WANDP, to facilitate its solution, the topological design problem is divided into three subproblems:


Topological Properties and Dynamic Programming Approach for Designing the Access Network DOI: http://dx.doi.org/10.5772/intechopen.86223

3.The routing (or flow assignment) and capacity assignment problem (RCAP)

The remainder of this work concentrates only in the first problem (ANDP).
