Towards user-centric metrics for denial-of-service measurement

To date, the measurement of user-perceived degradation of quality of service during denial of service (DoS) attacks remained an elusive goal. Current approaches mostly rely on lower level traffic measurements such as throughput, utilization, loss rate, and latency. They fail to monitor all traffic parameters that signal service degradation for diverse applications, and to map application quality-of-service (QoS) requirements into specific parameter thresholds. To objectively evaluate an attack's impact on network services, its severity and the effectiveness of a potential defense, we need precise, quantitative and comprehensive DoS impact metrics that are applicable to any test scenario. We propose a series of DoS impact metrics that measure the QoS experienced by end users during an attack. The proposed metrics consider QoS requirements for a range of applications and map them into measurable traffic parameters with acceptable thresholds. Service quality is derived by comparing measured parameter values with corresponding thresholds, and aggregated into a series of appropriate DoS impact metrics. We illustrate the proposed metrics using extensive live experiments, with a wide range of background traffic and attack variants. We successfully demonstrate that our metrics capture the DoS impact more precisely than the measures used in the past.