A survey of performance enhancement of transmission control protocol (TCP) in wireless ad hoc networks

This Article is provided by the Brunel Open Access Publishing Fund - Copyright @ 2011 Springer OpenTransmission control protocol (TCP), which provides reliable end-to-end data delivery, performs well in traditional wired network environments, while in wireless ad hoc networks, it does not perform well. Compared to wired networks, wireless ad hoc networks have some specific characteristics such as node mobility and a shared medium. Owing to these specific characteristics of wireless ad hoc networks, TCP faces particular problems with, for example, route failure, channel contention and high bit error rates. These factors are responsible for the performance degradation of TCP in wireless ad hoc networks. The research community has produced a wide range of proposals to improve the performance of TCP in wireless ad hoc networks. This article presents a survey of these proposals (approaches). A classification of TCP improvement proposals for wireless ad hoc networks is presented, which makes it easy to compare the proposals falling under the same category. Tables which summarize the approaches for quick overview are provided. Possible directions for further improvements in this area are suggested in the conclusions. The aim of the article is to enable the reader to quickly acquire an overview of the state of TCP in wireless ad hoc networks.This study is partly funded by Kohat University of Science & Technology (KUST), Pakistan, and the Higher Education Commission, Pakistan

Optimal screening for increased risk for adverse outcomes in hospitalised older adults

Background: screening for frailty might help to prevent adverse outcomes in hospitalised older adults. Objective: to identify the most predictive and efficient screening tool for frailty. Design and setting: two consecutive observational prospective cohorts in four hospitals in the Netherlands. Subjects: patients aged ≥70 years, electively or acutely hospitalised for ≥2 days. Methods: screening instruments included in the Dutch Safety Management Programme [VeiligheidsManagementSysteem (VMS)] on four geriatric domains (ADL, falls, undernutrition and delirium) were used and the Identification of Seniors At Risk, the 6-item Cognitive Impairment Test and the Mini-Mental State Examination were assessed. Three months later, adverse outcomes including functional decline, high-healthcare demand or death were determined. Correlation and regression tree analyses were performed and predictive capacities were assessed. Results: follow-up data were available of 883 patients. All screening instruments were similarly predictive for adverse outcome ( predictive power 0.58–0.66), but the percentage of positively screened patients (13–72%), sensitivity (24–89%) and specificity (35–91%) highly differed. The strongest predictive model for frailty was scoring positive on ≥3 VMS domains if aged 70–80 years; or being aged ≥80 years and scoring positive on ≥1 VMS domains. This tool classified 34% of the patients as frail with a sensitivity of 68% and a specificity of 74%. Comparable results were found in the validation cohort. Conclusions: the VMS-tool plus age (VMS+ ) offers an efficient instrument to identify frail hospitalised older adults at risk for adverse outcome. In clinical practice, it is important to weigh costs and benefits of screening given the rather low-predictive power of screening instruments

A survey of performance enhancement of transmission control protocol (TCP) in wireless <it>ad hoc </it>networks

Abstract Transmission control protocol (TCP), which provides reliable end-to-end data delivery, performs well in traditional wired network environments, while in wireless ad hoc networks, it does not perform well. Compared to wired networks, wireless ad hoc networks have some specific characteristics such as node mobility and a shared medium. Owing to these specific characteristics of wireless ad hoc networks, TCP faces particular problems with, for example, route failure, channel contention and high bit error rates. These factors are responsible for the performance degradation of TCP in wireless ad hoc networks. The research community has produced a wide range of proposals to improve the performance of TCP in wireless ad hoc networks. This article presents a survey of these proposals (approaches). A classification of TCP improvement proposals for wireless ad hoc networks is presented, which makes it easy to compare the proposals falling under the same category. Tables which summarize the approaches for quick overview are provided. Possible directions for further improvements in this area are suggested in the conclusions. The aim of the article is to enable the reader to quickly acquire an overview of the state of TCP in wireless ad hoc networks.</p

SRPM: secure routing protocol for IEEE 802.11 infrastructure based wireless mesh networks

Infrastructure based IEEE 802.11 wireless mesh networks (WMNs) are new paradigm of low cost broadband technology. The large scale city-wide community-based coverage and multi-hop architecture are such characteristics which are vulnerable to network layer threats, and the adversary can exploit them for large scale degradation of the broadband services. So far many secure routing protocols have been proposed for ad-hoc networks, however, due to the different nature and characteristics; they cannot perform well in a WMN environment. In this paper, we discuss the limitations and challenges as well as propose an exclusive secure routing protocol for an infrastructure based wireless mesh (SRPM) network. SRPM is robust against a variety of multi-hop threats and performs well over a range of scenarios we tested

Validity of a screening method for delirium risk in older patients admitted to a general hospital in the Netherlands

Objective: Delirium is an impactful, frequently occurring complication in older hospital patients. Consequently, risk stratification of delirium was included in a set of mandatory safety measures in general hospitals in the Netherlands. This risk stratification contains three consensus-based questions that have not been validated. Therefore, we evaluated their predictive performance and examined whether other routinely collected patient data can improve the prediction of delirium. Method: Using data from a continuous data registry from a general hospital, the prediction of the three questions was compared with the occurrence of delirium in 3786 older patients. Regression models were fitted that included other patient-related delirium risk factors. The performance was expressed by discrimination and calibration. Results: Delirium occurrence was 16.8%. The three questions, a regression model with the three questions, a full model and a reduced model – including the three questions, age, use of glasses, number of medications and Katz-ADL – showed sensitivities of 0.88, 0.88, 0.92 and 0.91 and specificities of 0.52, 0.52, 0.53 and 0.54, when treated as dichotomous models respectively. The three risk models had C-statistics of 0.81, 0.86 and 0.86, with excellent p-values of the U-statistics. Conclusion: The three risk-stratification questions show promising results but substantial overprediction (49% predicting positive). Further validation should be done outside the Netherlands, given the potential bias as a result of clinical activities following the risk stratification. The reduced model shows excellent calibration performance, indicating good prediction in each individual patient. In clinical practice, this advantage adds to clinical reasoning

HELP! Problems in executing a pragmatic, randomized, stepped wedge trial on the Hospital Elder Life Program to prevent delirium in older patients

Background: A pragmatic, stepped wedge trial design can be an appealing design to evaluate complex interventions in real-life settings. However, there are certain pitfalls that need to be considered. This paper reports on the experiences and lessons learned from the conduct of a cluster randomized, stepped wedge trial evaluating the effect of the Hospital Elder Life Program (HELP) in a Dutch hospital setting to prevent older patients from developing delirium. Methods: We evaluated our trial which was conducted in eight departments in two hospitals in hospitalized patients aged 70 years or older who were at risk for delirium by reflecting on the assumptions that we had and on what we intended to accomplish when we started, as compared to what we actually realized in the different phases of our study. Lessons learned on the design, the timeline, the enrollment of eligible patients and the use of routinely collected data are provided accompanied by recommendations to address challenges. Results: The start of the trial was delayed which caused subsequent time schedule problems. The requirement for individual informed consent for a quality improvement project made the inclusion more prone to selection bias. Most units experienced major difficulties in including patients, leading to excluding two of the eight units from participation. This resulted in failing to include a similar number of patients in the control condition versus the intervention condition. Data on outcomes routinely collected in the electronic patient records were not accessible during the study, and appeared to be often missing during analyses. Conclusions: The stepped wedge, cluster randomized trial poses specific risks in the design and execution of research in real-life settings of which researchers should be aware to prevent negative consequences impacting the validity of their results. Valid conclusions on the effectiveness of the HELP in the Dutch hospital setting are hampered by the limited quantity and quality of routine clinical data in our pragmatic trial. Executing a stepped wedge design in a daily practice setting using routinely collected data requires specific attention to ethical review, flexibility, a spacious time schedule, the availability of substantial capacity in the research team and early checks on the data availability and quality. Trial registration Netherlands Trial Register, identifier: NTR3842. Registered on 24 January 2013

Channel Contention-Based Routing Protocol for Wireless Ad Hoc Networks

With the development of wireless technology, two basic wireless network models that are commonly used, known as infrastructure and wireless ad hoc networks (WANETs), have been developed. In the literature, it has been observed that channel contention is one of the main reasons for packet drop in WANETs. To handle this problem, this paper presents a routing protocol named CCBR (Channel Contention Based Routing). CCBR tries to determine a least contended path between the endpoints to increase packet delivery ratio and to reduce packet delay and normalized routing overhead. Moreover, throughout the active data section, each intermediate node computes its channel contention value. If an intermediate node detects an increase in channel contention, it notifies the source node. Then the source node determines another least contended route for transmission. The advantages of CCBR are verified in our NS2-based performance study, and the results show that CCBR outperforms ad hoc on-demand distance vector (AODV) in terms of packet delivery ratio, end-to-end delay, and routing overhead by 4% to 9%