TCP deadlock due to coarse timer granularities in Unix-basedsystems

While it is usually assumed that packet schedulers in routers have sufficiently fine-grain timers, network systems frequently have timers of coarse granularity. An investigation into QoS failures that occur due to coarse timer granularities is presented. Based on the investigation, two methods for solving the problems are presented     

Resource management policies for fixed relays in cellular networks

Mobile stations in the cell boundary experience poor spectral efficiency due to the path loss and interference from adjacent cells. Therefore, satisfying QoS requirements of each MS at the cell boundary has been an important issue. To resolve this spectral efficiency problem at the cell boundary, deploying fixed relay stations has been actively considered. In this paper, we consider radio resource management policies concerned with fixed relays that include path selection rules, frequency reuse pattern matching, and frame transmission pattern matching among cells. We evaluate performance of each policy by varying parameter values such as relay station’s position and frequency reuse factor. Through Monte Carlo simulations and mathematical analysis, we suggest some optimal parameter values for each policy and discuss some implementation issues that need to be considered in practical deployment of relay stations.     

Relationship between prolonged standing and symptoms of varicose veins and nocturnal leg cramps among women and men

The relationships between occupational characteristics and symptoms of varicose veins and nocturnal leg cramps and their gender differences were explored in a Korean population. The study population was 2165 workers from various occupations (55.6% female). Multiple logistic regression analyses were conducted to reveal factors related to symptoms of varicose veins and nocturnal leg cramps. The prevalence of varicose veins and nocturnal leg cramps was higher among women than men. The characteristics of standing work were different according to gender. In gender stratified analysis, the odds ratio of varicose veins was significantly high for prolonged standing for male and female workers. However, the odds ratio of nocturnal leg cramps was only significant among prolonged standing male workers. The models including gender, prolonged standing and occupations in this order presented that gender is not significantly associated with varicose veins after occupations were added to the model. Prolonged standing at work may be a more important risk factor for varicose veins and nocturnal leg cramps than biological differences between women and men. Therefore, effective interventions to interrupt or reduce prolonged standing at work should be implemented for the prevention of varicose veins and nocturnal leg cramps. PRACTITIONER SUMMARY: This paper shows associations between occupational characteristics and symptoms of varicose veins and nocturnal leg cramps and their gender differences. These findings will contribute to knowledge of gender-specific occupational risk factors for symptoms in the distal lower extremities.     

Optimal Hop Extended MAC protocol for wireless sensor networks

In wireless sensor MAC protocols, duty cycling has been exploited to put sensor nodes into sleeping state most of the time, thereby saving the limited battery efficiently. In this paper, we present a MAC protocol called Hop Extended MAC (HE-MAC) that enables a source node to transmit a data packet for multiple hops in a single duty cycle. It employs an EXP (Explorer) frame to set up the path for multiple hop transmission, which contains the information about the maximum number of hops that a packet can travel through in a single duty cycle. Using this information and an internal state of Ready-to-Receive (RTR), HE-MAC relays the packet beyond the termination of the data period. Along with our adaptive sleeping method, it additionally reduces power consumption. Then, we analytically obtain the packet latency of HE-MAC and find its optimal wakeup duration with respect to packet latency. Through ns-2 simulations, we observe that HE-MAC achieves 42.2% less power consumption and 23.6% less packet delay on average compared to RMAC [9] for a random topology of 300 nodes. With the allocated optimal wakeup duration, the latency of HE-MAC is reduced by 54.3% at maximum and 41.1% on average, compared to the case of default setting.     

Origin of inhomogeneity in spark plasma sintered bismuth antimony telluride thermoelectric nanocomposites

Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices. However, the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far. Herein, we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride (BiSbTe) thermoelectric nanocomposites fabricated from solution-synthesized nanoplates. The figure of merit can reach 1.18, which, however, can be overestimated to 1.88 without considering the inhomogeneity. Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity, textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations. This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.

     

Profit-Based Routing for Multihop Coverage Extension in Wireless Networks

In future wireless systems, the coverage of a base station will decrease due to the characteristics of the channel at high-frequency bands. To expand the service coverage, a hybrid network that combines an ad hoc network with a cellular (or wireless LAN) network, appears to have great potential. In such systems, some mobile users outside the service area can access the network with the aid of other intermediate mobiles. However, this method incurs energy consumption in routing users, which could be a serious obstacle for wide-spread deployment of multihop wireless networks. Therefore we consider a revenue-cost model and propose a profit-based routing strategy that encourages routing users to actively participate in the relaying service because they are compensated for their energy consumption cost. Our strategy enables each mobile node to find an appropriate multihop path to a base station (or access point) that satisfies the interests of the service provider and the users. Numerical results show that our model successfully expands the network coverage area while ensuring the profit of each system involved.     

Real-time visualization of network attacks on high-speed links

This article shows that malicious traffic flows such as denial-of-service attacks and various scanning activities can be visualized in an intuitive manner. A simple but novel idea of plotting a packet using its source IP address, destination IP address, and the destination port in a 3-dimensional space graphically reveals ongoing attacks. Leveraging this property, combined with the fact that only three header fields per each packet need to be examined, a fast attack detection and classification algorithm can be devised.     

Utility-based downlink power allocation in multicell wireless packet networks

This paper introduces a utility-based radio resource management technique in multicell wireless packet networks. In terms of allocation of base station (BS) downlink transmit power and assignment of resource to users in each cell, we formulate a problem of maximizing system utility which is defined as the sum of cell utilities. The problem, however, is not solvable due to its non-convex property. Thus, we propose a heuristic algorithm based on an intuition obtained from analyzing a simple two-cell problem. Though the heuristic approach also incurs signaling overhead for power coordination between neighboring base stations, it is much less than that of the original approach. Simulation results show the performance of our proposed algorithm compared with two competitive schemes: optimal and maximum power allocation schemes. As expected, the optimal allocation scheme shows the best performance but can not be employed in a real network due to intractable complexity. Our heuristic algorithm performs reasonably well with very low complexity.