Junhua Tang

Gossip-based scalable directed diffusion for wireless sensor networks

Directed diffusion (DD) is a promising data-centric routing scheme for wireless sensor networks (WSNs). But the heavy flooding overhead involved in interest propagation causes scalability issues when DD is applied in large scale, interactive and dynamically changing sensor networks. To solve this problem, we propose a scalable version of DD called gossip-based scalable directed diffusion (GSDD) in this paper. GSDD uses the same routing framework as DD but integrates gossiping in interest propagation and employs dynamic regional gossiping in path exploration phase to reduce the flooding overhead. Our analysis and simulation results demonstrate that GSDD is able to reduce the data delivery cost of DD by up to 25%; thus, significantly reduce energy consumption and prolong the lifetime of sensor nodes. Therefore, GSDD overcomes the scalability problem of DD and is suitable for large-scale WSNs. Copyright

Optical nonlinear effects on the performance of IP traffic over GMPLS-based DWDM networks

With the introduction of Generalized multiprotocol label switching in the common control plane for optical crossconnects and electrical switching devices, the integration of IP and dense wavelength division multiplexing can be efficiently achieved. When IP traffic flows are directly mapped to optical channels without SDH inter-layer, the bursty nature of IP traffic may have significant effect on the performance of the optical channel. On the other hand, the nonlinear effects of the optical channel may also have significant effect on the performance at IP level. This paper focuses on the effect of fiber nonlinearities on the performance of IP traffic. Numerical results including IP packet error probability and high-order distribution functions of IP packet error are presented in terms of IP traffic load, input light signal power and the frequency space between the optical wavelengths. It is demonstrated that when IP traffic load is light in such systems, the effect of either four-wave mixing (FWM) or stimulated Raman scattering (SRS) is much less serious than the worst-case assumption, and the limitation on allowable power of input light is also relaxed. The obtained numerical results demonstrated that FWM and SRS are both sensitive to power level of input light and frequency spacing, but each in a unique way. Effort must be taken in system design to avoid improving the performance of one effect at the expense of deteriorating the other.

The effect of IP traffic on WDM-based networks

In this letter me show that when IP traffic is loaded directly over WDM-based networks, the burstiness of the IP packets can have significant effects on the network performance through its influence on the fiber nonlinear effects, mainly the four-wave mixing effect provided the fiber input light power is high, the frequency spacing is narrow and IP traffic load is heavy.

Providing Differentiated Services Over Shared Wireless Downlink Through Buffer Management

In this paper, we present an opportunistic packet scheduling algorithm based on buffer management (OSBM) over the downlink of a packet cellular network. OSBM is a channel-dependent scheduling algorithm with a provable delay bound. It is able to provide differentiated services to both real-time and nonreal-time applications. Particularly, these features of OSBM are achieved through a novel buffer management scheme. Since this buffer management scheme does not involve any complex online computation, OSBM is very efficient and easy to implement in an operational environment. We also present a new analytical approach for performance analysis of opportunistic scheduling in wireless networks based on the proposed concept of effective downlink capacity (EDC). This approach attempts to adapt the service curve tool for deterministic quality-of-service analysis to the wireless environment, and the concept of the EDC serves to bridge the deterministic method and the stochastic nature of the wireless link. Using this approach, the explicit expression of the delay bound of the OSBM algorithm is obtained. Simulation results are presented to demonstrate the effectiveness of the proposed opportunistic scheduling algorithm.

An Opportunistic Scheduling Algorithm for MPEG Video Over Shared Wireless Downlink

This paper presents a novel video scheduling algorithm for streaming MPEG video over multi-user shared wireless link, in which video sessions are scheduled based on both location-dependent channel condition and instantaneous frame delay. This algorithm also employs a pro-active frame discard mechanism to discard potential problematic frames. The numerical results show that the proposed algorithm is able to significantly improve link throughput and guarantee long-term fairness.

Optimal power allocation policy over two identical Gilbert-Elliott channels

We study the fundamental problem of optimal power allocation over two identical Gilbert-Elliott (Binary Markov) communication channels. Our goal is to maximize the expected discounted number of bits transmitted over an infinite time span by judiciously choosing one of the four actions for each time slot: 1) allocating power equally to both channels, 2) allocating all the power to channel 1, 3) allocating all the power to channel 2, and 4) allocating no power to any of the channels. As the channel state is unknown when power allocation decision is made, we model this problem as a partially observable Markov decision process(POMDP), and derive the optimal policy which gives the optimal action to take under different possible channel states. Two different structures of the optimal policy are derived analytically and verified by linear programming simulation. We also illustrate how to construct the optimal policy by the combination of threshold calculation and linear programming simulation once system parameters are known.

Note on Studying Change Point of LRD Traffic Based on Li's Detection of DDoS Flood Attacking

Distributed denial-of-serviceDDoSflood attacks remain great threats to the Internet. To ensure network usability and reliability, accurate detection of these attacks is critical. Based on Lis work on DDoS flood attack detection, we propose a DDoS detection method by monitoring the Hurst variation of long-range dependant traffic. Specifically, we use an autoregressive system to estimate the Hurst parameter of normal traffic. If the actual Hurst parameter varies significantly from the estimation, we assume that DDoS attack happens. Meanwhile, we propose two methods to determine the change point of Hurst parameter that indicates the occurrence of DDoS attacks. The detection rate associated with one method and false alarm rate for the other method are also derived. The test results on DARPA intrusion detection evaluation data show that the proposed approaches can achieve better detection performance than some well-known self-similarity-based detection methods.

A Grid Trust Model Based On MADM Theory

In this paper, we propose a trust model for the open Grid market. Our trust model emphasizes the importance of both direct trust and indirect trust/reputation when evaluating the trustworthiness of a Grid service provider. Since many factors contribute to the direct and indirect trust, we propose a novel method based on multiple attribute decision making (MADM) theory to determine the objective weights of both direct and indirect trust. The simulation results demonstrate that our trust model reflects the trustworthiness of a service provider more accurately than the weighted feedback model and eBay trust model, and thus improves user satisfaction in the open Grid environment.

An opportunistic video scheduling algorithm over shared wireless downlink

This paper presents a novel video scheduling algorithm for streaming MPEG video over multi-user shared wireless link, in which video sessions are scheduled based on both location-dependent channel condition and instantaneous frame delay. This algorithm also employs a pro-active frame discard mechanism to discard potential problematic frames. The numerical results show that the proposed algorithm is able to significantly improve link throughput and guarantee long-term fairness.

Characterization and performance study of IP traffic in WDM networks

This paper investigates the characteristics of network performance, when IP traffic is directly mapped into WDM networks using multi-protocol label switching (MPLS) techniques. The performance analysis focuses on the burstiness of IP traffic that may have a remarkable effect on the network performance. On the other hand, the inter-channel interferences caused by fiber nonlinear effect such as four wave mixing are also considered in the performance analysis. The statistics of network performance in terms of packet error probability, packet error free-run distribution and packet error-pattern distribution are presented. These illustrative results provide valuable information to the network designers.