Failure Criteria and the Relationship Between Quality of Service and Dependability in Telecommunications

In modern networks, quality of service and dependability play an important role. The paper examines the relationship between these concepts. The central place is given to the consideration of the failure criteria, which are necessary for the correct setting of quality of service and dependability requirements and their assessment. In telecommunications, a parametric approach is commonly used to formulate failure criteria. This means that decision parameters and thresholds for them are selected, exceeding which is considered a failure. The choice of decision parameters, their number and duration of evaluation are discussed. The failure criteria formulated in ITU-T Recommendations for a number of situations are analyzed. The presence of time over thresholds in them is shown and explained. The hysteresis effect is revealed in most of them. The shortcomings of some criteria are indicated. The expediency of the one-parameter approach is substantiated.