Chapter 6: Using the Availability Level as a Decision Criterion

Overview

In Chapter 4 the application of queuing theory to determining transmission delays through remote bridges and routers was examined. As noted in that chapter, you can use queuing theory to compare the use of single versus multiple circuits used to connect remote bridges and routers. In doing so, you examined the use of single and multiple circuits from a performance perspective, leaving until this chapter a discussion of availability issues.

One of the more important decisions that network managers and LAN administrators face is determining whether to install single or multiple port devices such as remote bridges and routers. By understanding how availability is computed, you obtain the knowledge necessary to determine whether or not the cost of additional bridge or router ports, communications equipment, and transmission facilities is worthwhile with respect to the additional level of network availability obtained through the use of different communications configurations.

This chapter focuses attention on the use of the availability level of different network configurations as a decision criterion. That decision criteria can range from the direct selection of one configuration over another based upon their level of availability to the use of several selection parameters, to include such additional parameters as performance and cost.