An Automatic and Dynamic Parameter Tuning of a Statistics-Based Anomaly Detection Algorithm

The detection of anomalies in network traffic is a crucial issue affecting the security of Internet users. A statistical network anomaly detection algorithm is a promising way of detecting such anomalies, however, it has to be given appropriate parameters for accurate detection and identification. In general, it is very difficult to obtain appropriate parameter settings a priori, because network traffic is not stable in time or space. Thus, although many anomaly detection methods have been proposed, there has been little discussion about their parameter tunings. In this paper, we investigate an automatic and dynamic parameter tuning of a statistical network traffic anomaly detection method. In particular, we clarify whether one can consistently use the best parameter fixed for a certain instance; this choice clearly depends on the macroscopic and dynamic behavior of Internet traffic anomalies. We ascertain the appropriate learning period for setting a parameter of an anomaly detection algorithm based on a sketch and multi-scale gamma-function model by using real network traces measured in a trans-Pacific link over a period of six months. The main results of our study are as follows: (1) Without learning, the best parameter varies day by day. (2) With a longer learning period, the best parameter setting is affected by significant data during the learning period. (3) The appropriate period of the learning is about 3 days. (4) The performance degradation from introducing dynamic parameter tuning is 17% in the best case.