We present a method to detect anomalies in a time series of flow interaction patterns. There are many existing methods for anomaly detection in network traffic, such as number of packets. However, there is non established method detecting anomalies in a time series of flow interaction patterns that can be represented as complex network. Firstly, based on proposed multivariate flow similarity method on temporal locality, a complex network model (MFS-TL) is constructed to describe the interactive behaviors of traffic flows. Having analyzed the relationships between MFS-TL characteristics, temporal locality window and multivariate flow similarity critical threshold, an approach for parameter determination is established. Having observed the evolution of MFS-TL characteristics, three non-deterministic correlations are defined for network states (i.e. normal or abnormal). Furthermore, intuitionistic fuzzy set (IFS) is introduced to quantify three non-deterministic correlations, and then a anomaly detection method is put forward for single characteristic sequence. To build an objective IFS, we design a Gaussian distribution-based membership function with a variable hesitation degree. To determine the mapping of IFS's clustering intervals to network states, a distinction index is developed. Then, an IFS ensemble method (IFSE-AD) is proposed to eliminate the impacts of the inconsistent about MFS-TL characteristic to network state and improve detection performance. Finally, we carried out extensive experiments on several network traffic datasets for anomaly detection, and the results demonstrate the superiority of IFSE-AD to state-of-the-art approaches, validating the effectiveness of our method.
Network traffic anomalies are instances in data that do not conform to the behavior exhibited by normal traffic. Traffic anomalies in a network can be defined as any network events or operation that deviate from the normal network behavior. They happen due to the growing number of network-based attacks or intrusions. Nowadays, the network anomaly detection methods can be classified into the statistic-, classification-, clustering-, soft computing-, fuzzy set theory-, and combination learners-based @cite_21 @cite_42 . In general, the first step is that the raw data is reduced by one of the three important strategies, i.e. dimensionality reduction (e.g. feature selection and feature extraction), clustering, and sampling, on packet-level, flow-level or host-level. However, the selected features or quantified metrics are usually used as the individual indicator @cite_55 @cite_41 @cite_45 @cite_32 .
@cite_41 @cite_55 @cite_21 @cite_42 @cite_32 @cite_45
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The increasing practicality of large-scale flow capture makes it possible to conceive of traffic analysis methods that detect and identify a large and diverse set of anomalies. However the challenge of effectively analyzing this massive data source for anomaly diagnosis is as yet unmet. We argue that the distributions of packet features (IP addresses and ports) observed in flow traces reveals both the presence and the structure of a wide range of anomalies. Using entropy as a summarization tool, we show that the analysis of feature distributions leads to significant advances on two fronts: (1) it enables highly sensitive detection of a wide range of anomalies, augmenting detections by volume-based methods, and (2) it enables automatic classification of anomalies via unsupervised learning. We show that using feature distributions, anomalies naturally fall into distinct and meaningful clusters. These clusters can be used to automatically classify anomalies and to uncover new anomaly types. We validate our claims on data from two backbone networks (Abilene and Geant) and conclude that feature distributions show promise as a key element of a fairly general network anomaly diagnosis framework. We introduce an Internet traffic anomaly detection mechanism based on large deviations results for empirical measures. Using past traffic traces we characterize network traffic during various time-of-day intervals, assuming that it is anomaly-free. We present two different approaches to characterize traffic: (i) a model-free approach based on the method of types and Sanov's theorem, and (ii) a model-based approach modeling traffic using a Markov modulated process. Using these characterizations as a reference we continuously monitor traffic and employ large deviations and decision theory results to ldquocomparerdquo the empirical measure of the monitored traffic with the corresponding reference characterization, thus, identifying traffic anomalies in real-time. Our experimental results show that applying our methodology (even short-lived) anomalies are identified within a small number of observations. Throughout, we compare the two approaches presenting their advantages and disadvantages to identify and classify temporal network anomalies. We also demonstrate how our framework can be used to monitor traffic from multiple network elements in order to identify both spatial and temporal anomalies. We validate our techniques by analyzing real traffic traces with time-stamped anomalies. With the rapid growth and the increasing complexity of network infrastructures and the evolution of attacks, identifying and preventing network abuses is getting more and more strategic to ensure an adequate degree of protection from both external and internal menaces. In this scenario many techniques are emerging for inspecting network traffic and discriminating between anomalous and normal behaviors to detect undesired or suspicious activities. Unfortunately, the concept of normal or abnormal network behavior depends on several factors and its recognition requires the availability of a model aiming at characterizing current behavior, based on a statistical idealization of past events. There are two main challenges when generating the training data needed for effective modeling. First, network traffic is very complex and unpredictable, and second, the model is subject to changes over time, since anomalies are continuously evolving. As attack techniques and patterns change, previously gained information about how to tell them apart from normal traffic may be no longer valid. Thus, a desirable characteristic of an effective model for network anomaly detection is its ability to adapt to change and to generalize its behavior to multiple different network environments. In other words, a self-learning system is needed. This suggests the adoption of machine learning techniques to implement semi-supervised anomaly detection systems where the classifier is trained with ''normal'' traffic data only, so that knowledge about anomalous behaviors can be constructed and evolve in a dynamic way. For this purpose we explored the effectiveness of a detection approach based on machine learning, using the Discriminative Restricted Boltzmann Machine to combine the expressive power of generative models with good classification accuracy capabilities to infer part of its knowledge from incomplete training data. Detecting and understanding anomalies in IP networks is an open and ill-defined problem. Toward this end, we have recently proposed the subspace method for anomaly diagnosis. In this paper we present the first large-scale exploration of the power of the subspace method when applied to flow traffic. An important aspect of this approach is that it fuses information from flow measurements taken throughout a network. We apply the subspace method to three different types of sampled flow traffic in a large academic network: multivariate timeseries of byte counts, packet counts, and IP-flow counts. We show that each traffic type brings into focus a different set of anomalies via the subspace method. We illustrate and classify the set of anomalies detected. We find that almost all of the anomalies detected represent events of interest to network operators. Furthermore, the anomalies span a remarkably wide spectrum of event types, including denial of service attacks (single-source and distributed), flash crowds, port scanning, downstream traffic engineering, high-rate flows, worm propagation, and network outage.