Inadequate Reliability

Abstract

In chapter 16, the twin questions of reliability and security were discussed. A failure to attend to these points (and especially reliability) has spelled doom for too many data communications systems. The first point that needs to be highlighted is that reliability is a design feature. It is no use building some ‘back-up’ into a system after it has been designed. To take a simple example, the data communications links in a network may be planned to account for both normal and peak-load traffic, and the development and running costs may be justified on this basis. Subsequent analysis may reveal that to achieve the level of reliability required using the links provided by the telecommunications authorities requires additional links to be established purely for ‘back-up’ purposes. It is a natural reaction for management in these circumstances to continue to support the basic investment, but not to approve the ‘back-up’ investment. The network (and the systems that use it) are therefore not able to provide the degree of reliability required. The consequence — inevitably — is a failure of the system to meet its reliability criteria and the loss of credibility by the management services department.