Receiver-Based Flow Control for Networks in Overload

We consider utility maximization in networks where the sources do not employ flow control and may consequently overload the network. In the absence of flow control at the sources, some packets will inevitably have to be dropped when the network is in overload. To that end, we first develop a distributed, threshold-based packet dropping policy that maximizes the weighted sum throughput. Next, we consider utility maximization and develop a receiver-based flow control scheme that, when combined with threshold-based packet dropping, achieves the optimal utility. The flow control scheme creates virtual queues at the receivers as a push-back mechanism to optimize the amount of data delivered to the destinations via back-pressure routing. A novel feature of our scheme is that a utility function can be assigned to a collection of flows, generalizing the traditional approach of optimizing per-flow utilities. Our control policies use finite-buffer queues and are independent of arrival statistics. Their near-optimal performance is proved and further supported by simulation results.Comment: 14 pages, 4 figures, 5 tables, preprint submitted to IEEE INFOCOM 201

Throughput-Optimal Multihop Broadcast on Directed Acyclic Wireless Networks

We study the problem of efficiently broadcasting packets in multi-hop wireless networks. At each time slot the network controller activates a set of non-interfering links and forwards selected copies of packets on each activated link. A packet is considered jointly received only when all nodes in the network have obtained a copy of it. The maximum rate of jointly received packets is referred to as the broadcast capacity of the network. Existing policies achieve the broadcast capacity by balancing traffic over a set of spanning trees, which are difficult to maintain in a large and time-varying wireless network. We propose a new dynamic algorithm that achieves the broadcast capacity when the underlying network topology is a directed acyclic graph (DAG). This algorithm is decentralized, utilizes local queue-length information only and does not require the use of global topological structures such as spanning trees. The principal technical challenge inherent in the problem is the absence of work-conservation principle due to the duplication of packets, which renders traditional queuing modelling inapplicable. We overcome this difficulty by studying relative packet deficits and imposing in-order delivery constraints to every node in the network. Although in-order packet delivery, in general, leads to degraded throughput in graphs with cycles, we show that it is throughput optimal in DAGs and can be exploited to simplify the design and analysis of optimal algorithms. Our characterization leads to a polynomial time algorithm for computing the broadcast capacity of any wireless DAG under the primary interference constraints. Additionally, we propose an extension of our algorithm which can be effectively used for broadcasting in any network with arbitrary topology

Throughput-Optimal Broadcast on Directed Acyclic Graphs

We study the problem of broadcasting packets in wireless networks. At each time slot, a network controller activates non-interfering links and forwards packets to all nodes at a common rate; the maximum rate is referred to as the broadcast capacity of the wireless network. Existing policies achieve the broadcast capacity by balancing traffic over a set of spanning trees, which are difficult to maintain in a large and time-varying wireless network. We propose a new dynamic algorithm that achieves the broadcast capacity when the underlying network topology is a directed acyclic graph (DAG). This algorithm utilizes local queue-length information, does not use any global topological structures such as spanning trees, and uses the idea of in-order packet delivery to all network nodes. Although the in-order packet delivery constraint leads to degraded throughput in cyclic graphs, we show that it is throughput optimal in DAGs and can be exploited to simplify the design and analysis of optimal algorithms. Our simulation results show that the proposed algorithm has superior delay performance as compared to tree-based approaches.Comment: To appear in the proceedings of INFOCOM, 201

The role of immunonutrients in the prevention of necrotizing enterocolitis in preterm very low birth weight infants

Necrotizing enterocolitis (NEC) is a critical intestinal emergency condition, which mainly occurs in preterm very low birth weight (PVLBW) infants. Despite remarkable advances in the care of PVLBW infants, with considerable improvement of the survival rate in recent decades, the incidence of NEC and NEC-related mortality have not declined accordingly. The fast progression from nonspecific signs to extensive necrosis also makes primary prevention the first priority. Recently, increasing evidence has indicated the important role of several nutrients in primary prevention of NEC. Therefore, the aim of this review is to summarize some potential immunomodulatory nutrients in the prevention of NEC, including bovine colostrum, probiotics, prebiotics (e.g., human milk oligosaccharides), long chain polyunsaturated fatty acids, and amino acids (glutamine, cysteine and N-acetylcysteine, l-arginine and l-citrulline). Based on current research evidence, probiotics are the most documented effective method to prevent NEC, while others still require further investigation in animal studies and clinical randomized controlled trials

Quality of life among older people in the UK and Taiwan.

This research is a cross-national comparison of longitudinal studies, designed to compare the quality of life, to identify the physical, mental, social, environmental factors contributing to quality of life, and predict the relationship between quality of life and mortality in old age. Although previous research has suggested that health, functional ability, psychological well-being, social relationships, socioeconomic status, and environmental conditions can affect quality of life among older people, little research has compared quality of life in old age across Asia-Western countries. The overall aim of this study was to compare the factors affecting quality of life among older people in the UK and Taiwan. Data were derived from the 1989 and 1993 waves of two nationally-representative samples of older people: the Nottingham Longitudinal Study of Activity and Ageing (NLSAA) in the UK, and the Survey of Health and Living Status of the Elderly in Taiwan. Data from the two studies were harmonised to ensure their comparability for the statistical analyses, and life satisfaction was used as a measure of quality of life. Secondary analysis was performed on the harmonised data sets containing data from 690 (1989) and 410 (1993) NLSAA participants and 1,438 (1989) and 1,003 (1993) SHLSET participants. Factors related to physical (e.g., self-rated health, perceived health relative to peers, specific diseases) and mental health (e.g., loneliness, depression), social factors (e.g., attending religious groups, having a TV or radio, having friends), demographic characteristics (e.g., age, gender, marital status, income), and life satisfaction (as a measure of quality of life) were examined using MannWhitney tests, chi-square tests, stepwise multiple regression, and logistic regression. The association between quality of life and mortality was assessed using Cox proportional hazards regression models. Cluster analysis was used to examine the patterns among older people in terms of life satisfaction, and the relationship of these clusters with mortality was assessed. The results of this research suggested that the sample of older people from the UK had higher life satisfaction scores than their peers in Taiwan; however, this difference did not remain in the multivariate analyses. The analyses also identified that self-rated health, mental health (loneliness and depression), income satisfaction, and using a walking aid were common predictors affecting quality of life in the two countries. The results from Chapter 5 showed that the study location variable had an interactional effect with particular variables on life satisfaction between the two countries, i.e., people in the UK who were married, had excellent self-rated health, smoked, had heart, stomach, dizziness, high blood pressure or walking problems, used a walking aid, and those with high level of depression. People in these groups in the UK tended to report a high level of life satisfaction compared with their counterparts in Taiwan. Older people in Taiwan without friends had lower life satisfaction than their counterparts who had no friends in the UK. Survival analyses showed that life satisfaction is associated with mortality in the two countries, especially older people who reported positive feelings in life satisfaction tended to have a decreased risk of mortality. Life satisfaction had a less persistent effect on mortality for the sample of older people in Taiwan, suggesting that other factors explain the relationship with mortality in older people in Taiwan, or that they are more resilient. However, in the UK people who had higher life satisfaction scores had improved survival, independent of demographic, physical and mental health, and social engagement. There was no relationship between change in life satisfaction (1989-1993) and mortality. Finally, patterns of life satisfaction were related to mortality - older people with patterns of higher life satisfaction within cluster were more likely to live longer. Statistically significant differences were found between most the of factors of life satisfaction in the two countries. For instance, older people in Taiwan tended to live with someone, suggesting that the extended families are more in Taiwan than the UK. While some of the differences found, such as depression and loneliness, may be due to cultural variations, further research is required to identify further predictors of life satisfaction. Finally, the term 'life satisfaction' is one component of quality of life, and life satisfaction was used as a measure of quality of life in the research. This comparative research described and explained the differences and similarities in quality of life among older people living in two different cultures and societies. To conclude, a common data set is a unique opportunity to identify the factors affecting quality of life and to compare quality of life between the UK and Taiwan for increasing our understanding of older people

Loop-Free Backpressure Routing Using Link-Reversal Algorithms

The backpressure routing policy is known to be a throughput optimal policy that supports any feasible traffic demand in data networks, but may have poor delay performance when packets traverse loops in the network. In this paper, we study loop-free backpressure routing policies that forward packets along directed acyclic graphs (DAGs) to avoid the looping problem. These policies use link reversal algorithms to improve the DAGs in order to support any achievable traffic demand. For a network with a single commodity, we show that a DAG that supports a given traffic demand can be found after a finite number of iterations of the link-reversal process. We use this to develop a joint link-reversal and backpressure routing policy, called the loop free backpressure (LFBP) algorithm. This algorithm forwards packets on the DAG, while the DAG is dynamically updated based on the growth of the queue backlogs. We show by simulations that such a DAG-based policy improves the delay over the classical backpressure routing policy. We also propose a multicommodity version of the LFBP algorithm, and via simulation we show that its delay performance is better than that of backpressure.National Science Foundation (U.S.) (Grant CNS-1116209)United States. Office of Naval Research (Grant N00014-12-1-0064