A data aggregation function in Internet-of-Things (IoT) systems summarizes a large amount of small segments of sensor data, and is effective for saving limited communication resources such as radio frequency and sensor node energy. In a previous study, we analyzed two fundamental statistical data aggregation schemes--constant interval and constant number schemes--and derived the Laplace-Stieltjes transforms of the system time and latency distributions for each scheme. Moreover, we derived simple and accurate estimation formulae for the optimal aggregation interval and number. In this paper, we analyze nonstatistical data aggregation with the constant number scheme. We analytically derive the Laplace-Stieltjes transforms and the averages of the system time and latency distributions. We find that the average latency can be minimized by tuning the traffic intensity in the transmission process that depends on the aggregation number, arrival rate, and transmission time of the data unit. Based on the clarified characteristics, we derive estimation formulae for the optimal aggregation number and optimal latency according to the traffic intensity that minimizes the average latency. Our main contribution is the theoretical basis for further research on the performance evaluation and design of communication devices, such as IoT gateways, which will be essential to realize latency- critical IoT applications.

Particle swarm optimization is very simple algorithm. However, the trajectory of each particle becomes pretty complicated because each particle is affected by the information of the other particles. In order to analyze the dynamics of the PSO rigorously, we propose the canonical deterministic PSO (CD-PSO). The CD-PSO is described by a canonical form, and the dynamics is characterized by the damping factor and the rotational angle. The dynamics of the CD-PSO can be analyzed theoretically, however, the solution search performance is worse than the conventional PSO. The reason why the performance of the CD-PSO is poor, is the rotation radius of the particle is decreased with the change of the best position. The small rotation radius contributes to the local search ability, but the global search ability is spoiled. Therefore, we propose a method to sustain the global search for the CD-PSO. The function is realized by maintaining the rotation radius. Applying the proposed method for the CD-PSO, the solution search performance improves that of the conventional CD-PSO.

In this paper, we analyze by theoretical calculation of the proposed scheme for collision detection in wireless local area networks (WLANs). The proposed scheme utilizes the medium access control (MAC) procedure of multiple input multiple output (MIMO) transmission technology, which is used to achieve high-speed transmission in WLANs in recent years; however, the transmission efficiency degrades at the MAC layer level, although a high transmission link rate is achieved at the physical (PHY) layer. The proposed scheme were performed high transmission efficiency of approximately 90% by the computer simulation in our previous work. In this paper, the results of our theoretical calculations correspond with the computer simulation results, indicating that the proposed scheme is indeed efficient and reliable.

Recently, the demand for content delivery in wired/wireless heterogeneous networks is increasing at a rapid pace. Content Distribution/Delivery Networks (CDNs) are considered to be one of the best solutions for dealing with this increasing demand. In this paper, we point out that the performance of a CDN typically degrades in such heterogeneous environments due to the changes in not only user demand but also wireless mobility, which triggers unexpected fluctuations in traffic. Wireless users, roaming between different access networks, may contribute to sudden and unexpected demand spikes in certain parts of the content delivery system. To address this issue, we develop a cooperative server selection scheme, which is designed to maximize robustness to such changes with the cooperation between the content delivery system and its users. The performance of our proposal is evaluated by extensive computer simulations. The evaluation results demonstrate that our proposed scheme effectively makes the considered content delivery system resilient against request fluctuations while minimizing system overloading.

Internet traffic volumes continue to increase rapidly with the spread of the broadband access and the increase in internet backbone capacities. Moreover, the applications provided over the internet have become more diverse. Adequately supporting the QoS requirements for these diverse applications requires measuring traffic volumes by application type(file transfer, broadcast and so on). Therefore, methods for classifying applications become extremely important for multi QoS environment. In some application traffic classification methods, the applications are analyzed on the basis of statistics for the traffic characteristics, such as the packet inter arrival time and packet size. In this paper, we propose application traffic classification method applying LPC cepstrum. The proposed method enables to treat the traffic data as a time series signal and to separate spectral envelope information and spectral fine structure information from spectrum. We show that it is effective to use the LPC cepstrum to classify internet traffic by comparing LPC cepstrum with flow and raw data in this paper.

When a link or node failure occurs in a network, flows are detoured and therefore the hop counts of the flows increase. This increase could drastically deteriorate the quality of a network. The flow hop length stability as well as network connectivity is important for network reliability. We investigate a network design method that improves stability and connectivity of a network during a failure with a limited investment cost. We formalize a network design problem, prove that this problem is NP-complete, and propose an approximation algorithm. In addition, we evaluate the performance of the algorithm by using publicly available data for 39 backbone networks of commercial ISPs and networks generated by two well-known models. The results show that the proposed algorithm provides effective solutions from a practical viewpoint in sufficiently small computation time.

It is known that there exist Triangle Inequality Violations (TIVs) with respect to network Quality of Service (QoS) metrics such as latency between nodes in the Internet. This motivates the exploitation of QoS-aware routing overlays. To find an optimal overlay route, we would usually need to examine all the possible overlay routes. However, this requires both measuring QoS between all node pairs and investigating all the routes in the full-mesh overlay topology, which poses scalability problem in terms of both measurement cost and route calculation and dissemination cost. We thus propose a method of constructing a QoS overlay network that enables us to find a near optimal route in a cost-effective manner. Our idea is based on the finding that a small number of overlay nodes can provide the optimal routes for a large number of node pairs, which is obtained through measurement data analysis between PlanetLab nodes. Our overlay network has two layers where the upper-layer consists of such small number of overlay nodes that can provide the optimal routes while the lower-layer consists of the other overlay nodes. By allocating such overlay nodes at the upper-layer, we can provide better QoS routes for each node pair with high probability. We construct the overlay network topology where the upper-layer overlay nodes are connected in full-mesh manner while the lower-layer overlay nodes are not connected in full-mesh but only to upper-layer nodes. Through this structure, we can reduce measurement and route calculation costs. Using PlanetLab data, we show that our method can achieve almost the same performance as the optimal solution.

It is known that Internet routing policies for both intra- and inter-domain routing can naturally give rise to triangle inequality violations (TIVs) with respect to quality of service (QoS) network metrics such as latencies between nodes. This motivates the exploitation of such TIVs phenomenon in network metrics to design TlV-aware routing overlay architecture which is capable of choosing quality overlay routing paths to improve end-to-end QoS without changing the underlying network architecture. Our idea is to find quality overlay routes between node pairs based on TIV optimization in terms of the latency and packet loss ratio, and that can offer near optimal routing quality in cost-effective and scalable manner. Our intuition to do this is to choose these overlay routes from a small set of transit nodes. We propose to assign nodes with transit selection frequency scores that are computed based on previous node usage for transit, and consolidate a small set of highly ranked transit nodes. For every node pair, we choose the best transit node in this small set for overlay routing, based on TIV optimization in latency and packet loss ratio. We analyze the quality of our TlV-aware routing overlay algorithm analytically and using real Internet measurements on latency and packet loss ratio. Our results show good quality performance in improving end-to-end QoS routing.

We present a method of detecting network anomalies, such as DDoS (distributed denial of service) attacks and flash crowds, automatically in real time. We evaluated this method using measured traffic data and found that it successfully differentiated suspicious traffic. In this paper, we focus on cyclic traffic, which has a daily and/or weekly cycle, and show that the differentiation accuracy is improved by utilizing such a cyclic tendency in anomaly detection. Our method differentiates suspicious traffic that has different statistical characteristics from normal traffic. At the same time, it learns about cyclic large- volume traffic, such as traffic for network operations, and finally considers it to be legitimate.

Voice over IP (VoIP) is becoming one of the key technologies for telecommunications. Since IP networks generally do not guarantee transmission quality, it is extremely important to design and manage the quality of service (QoS) properly. To do this, it is desirable to develop an objective quality assessment method that estimates subjective quality based on the physical characteristics of the VoIP system. This paper first proposes a framework of objective models that can be applied not only to quality planning, which is an intended application of the existing standard methodology known as International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) Recommendation G.107, "the E-model," but also to quality benchmarking and management. Then, it proposes a model that complies with the proposed framework. Experimental results show that the proposed model has sufficient accuracy in the evaluation of practical VoIP systems. In addition, we attempt to integrate the opinion model with other objective quality measures, such as perceptual evaluation of speech quality (PESQ), standardized in Recommendation P.862 in ITU-T. Finally, we examine the task dependence of the performance of the proposed model

This paper clarifies the effects of multiparty audiovisual communication quality factors - the quality imbalance and conversation roles - on overall quality and proposes a method of estimating overall quality taking them into account. First, we focused on packet loss and delay as quality degradation factors and performed a subjective quality assessment. The results showed that the overall quality at a given point is strongly influenced by inferior quality at other points and that the conversation roles influence the overall quality. Validation test results verified that the overall quality was estimated by the proposed method with sufficient accuracy for practical use. As a guideline for quality management and control for multiparty audiovisual communication, we show that improving the inferior other-point quality is an effective way to improve the overall quality.