1.6 Determining Availability Levels

Depending on the activities performed by your organization, you may be required to incorporate a degree of redundancy into your network structure . To do so you can simply acquire additional pairs of remote bridges or routers and connect them through the use of separate transmission facilities. As an alternative to duplicating certain network components , you can also consider the use of multiport bridges and routers, the cost of which is considerably less than separate devices. However, what is the difference in the level of availability provided by the use of dual port devices versus the use of separate devices? The answer to this question, as well as a detailed examination of the concept of availability, are the focus of Chapter 6.

Chapter 6 explains how mean time before failure (MTBF) and mean time to repair (MTTR) information ” usually available from vendor product specification sheets ” is used to determine both component and system availability levels. Concerning the latter, a portion of Chapter 6 illustrates how the availability level of a complex network can be reduced to a series of simple computations . Chapter 6 also includes the use of BASIC language programs and Excel templates to facilitate tedious computations and provides you with the ability to compute the availability level of devices and transmission facilities connected in series or in parallel. These programs and templates also serve as a mechanism to compute the availability level of a mixed topology network, or you can even use the information in this chapter to compare and contrast redundant and nonredundant computer hardware configurations. Using these programs, templates, or the calculation methods described in Chapter 6, you can obtain the information necessary to determine whether or not the cost of one network configuration versus another is worthwhile with respect to the additional level of network availability obtained through the use of different communications configurations.