Incidents with availability of telecom services often happen because of component failures: an underground cable is damaged by a contractor, a power failure causes equipment to shut down. To prepare for these incidents, the organisation must first realise that the cable and equipment exist. An important part of the Raster method is therefore to draw a diagram showing all components involved in delivering the service.
Incidents can also happen when a single event leads to the simultaneous failure of two or more components. For example, two cables in the same duct can be cut in the same incident, or a software update can cause several servers to misbehave. These failures are called common cause failures, and they are dangerous because their impact can be quite large.
Major steps in the Raster method are to draw service diagrams, and to assess the likelihood and potential impact of single and common cause failures. However, unlike other methods Raster does not take a narrow numerical approach to assessing risks.
Risks with low probability and high effects are especially important. These rare but catastrophic events have been called “black swans”. Raster helps to uncover black swans in telecom services.
Risk assessments are always in part subjective, and information is hardly ever as complete as analysts would like it to be. This does not mean that biases and prejudices are acceptable. Raster tries to nudge analysts into a critical mode of thinking. Uncertainty is normal, and assessments can be explicitly marked as “Unknown” or “Ambiguous” if a more specific assessment cannot be made. Raster can be applied even when much of the desired information on the composition of telecom networks is unavailable or unknown. Missing information can be gradually added.
To avoid a narrow risk assessment, the Raster method is applied by a team of experts, each having his own area of expertise. Raster facilitates cooperation between experts of different backgrounds.
Raster facilitates the construction of a recommendation using a tested methodical analysis. This recommendation is not just based on the technical aspects of failure of telecoms services, but also takes account of the societal impact of failures, and of risk perceptions of external stakeholders.
One final remark: Raster can be deployed on its own, or as part of a company-wide risk management framework. This manual assumes a stand-alone application. When Raster is used as an element within an approach, the initiation stage (in which the scope of the study is determined) will likely need to be adapted.
The following parties are involved in applying the Raster method.
The team needs to encompass knowledge on essential business activities and technical aspects of telecommunication networks and services. Additionally, it will be useful if team members have some experience with risk assessment, and with the Raster method in particular. Because of this range of knowledge it will be necessary to include employees of the case organisation in the team of analysts.
Software tools are available to support the application of the method. Their use is strongly recommended, and this manual assumes that one of these applications is used. There are multiple versions: there is a standalone application for Windows and MacOS, and a web-based tool that requires an intranet server. All versions function almost identically. This manual uses “the application” without specific reference to indicate that either version can be read.