IEEE 802.11 based wireless networks have seen rapid growth and deployment in the recent years. Critical to the 802.11 MAC operation, is the handoff function which occurs when a mobile node moves its association from one access point to another. In this paper, we present an empirical study of this handoff process at the link layer, with a detailed breakup of the latency into various components. In particular, we show that a MAC layer function -probe is the primary contributor to the overall handoff latency. In our study, we observe that the latency is significant enough to affect the quality of service for many applications (or network connections). Further we find a large variation in the latency with from one handoff to another and also among APs and STAs used from different vendors. In this study, we account for this variation and also draw the guidelines for future handoff schemes.
User mobility in wireless data networks is increasing because of technological advances, and the desire for voice and multimedia applications. These applications, however, require handoffs between base stations to be fast to maintain the quality of the connections. Previous work on context transfer for fast handoffs has focused on reactive, i.e. the context transfer occurs after the mobile station has associated with the next base station or access router, methods. In this paper, we describe the use of a novel and efficient data structure, neighbor graphs, which captures dynamically the mobility topology of a wireless network as a means for pre-positioning the station's context at the potential next base stations-ensuring that the station's context remains one hop ahead. From experimental and simulation results, we find that the use of neighbor graphs reduces the layer 2 handoff latency due to reassociation by an order of magnitude from 15.37ms to 1.69ms, and that the effectiveness of the approach improves dramatically as user mobility increases.
Abstract-The 802.11 IEEE Standard has enabled low cost and effective wireless LAN services (WLAN). With the sales and deployment of WLAN based networks exploding, many people believe that they will become the fourth generation cellular system (4G) or a major portion of it. However, the small cell size of WLAN networks creates frequent hand-offs for mobile users. If the latency of these hand-offs is high, as previous studies have shown, then the users of synchronous multimedia applications such as voice over IP (VoIP) will experience excessive jitter. The dominating factor in WLAN hand-offs has been shown to be the discovery of the candidate set of next access points. In this paper, we describe the use of a novel and efficient discovery method using neighbor graphs and overlap graphs. Our method reduces the total number probed channels as well as the total time spent waiting on each channel. Our implementation results show that this approach reduces the overall probe time significantly when compared to other approaches. Furthermore, simulation results show that the effectiveness of our method improves as the number of non-overlapping channels increases, such as in the 5 GHz band used by the IEEE 802.11a standard.
Aims/hypothesis The aims of the study were to evaluate the association between type 2 diabetes and the risk of death from any cancer and specific cancers in East and South Asians. Methods Pooled analyses were conducted of 19 prospective population-based cohorts included in the Asia Cohort Consortium, comprising data from 658,611 East Asians and 112,686 South Asians. HRs were used to compare individuals with diabetes at baseline with those without diabetes for the risk of death from any cancer and from site-specific cancers, including cancers of the oesophagus, stomach, colorectum, colon, rectum, liver, bile duct, pancreas, lung, breast, endometrium, cervix, ovary, prostate, bladder, kidney and thyroid, as well as lymphoma and leukaemia. Results During a mean follow-up of 12.7 years, 37,343 cancer deaths (36,667 in East Asians and 676 in South Asians) were identified. Baseline diabetes status was statistically significantly associated with an increased risk of death from any cancer (HR 1.26;95% CI1.21, 1.31). Significant positive associations with diabetes were observed for cancers of the colorectum(HR 1.41;95% CI 1.26, 1.57), liver (HR 2.05;95% CI 1.77, 2.38), bile duct (HR 1.41;95% CI 1.04, 1.92), gallbladder (HR 1.33; 95% CI1.10, 1.61), pancreas (HR 1.53; 95% CI1.32, 1.77), breast (HR 1.72; 95% CI1.34, 2.19), endometrium (HR 2.73; 95% CI1.53, 4.85), ovary (HR 1.60; 95% CI1.06, 2.42), prostate (HR 1.41; 95% CI1.09, 1.82), kidney (HR 1.84; 95% CI1.28, 2.64) and thyroid (HR 1.99; 95% CI1.03, 3.86), as well as lymphoma (HR 1.39; 95% CI1.04, 1.86). Diabetes was not statistically significantly associated with the risk of death from leukaemia and cancers of the bladder, cervix, oesophagus, stomach and lung. Conclusions/interpretation Diabetes was associated with a 26% increased risk of death from any cancer in Asians. The pattern of associations with specific cancers suggests the need for better control (prevention, detection, management) of the growing epidemic of diabetes (as well as obesity), in order to reduce cancer mortality.
The purpose of this study was to estimate the national prevalence of childhood asthma and other allergic diseases in Korea, and to determine potential risk factors for the diseases. Stratified random samples of 42,886 were selected from 34 elementary (6-12 yr olds) and 34 middle schools (12-15 yr olds) nationwide, and 38,955 were in the final analysis. The Korean-translated modified version of the International Study of Asthma and Allergies in Childhood questionnaire was used in this cross-sectional survey. Twelve-month prevalences of the symptoms of asthma, rhinoconjunctivitis, and flexural eczema were 8.7%, 10.5%, 7.3% in 6-12 yr olds, and 8.2%, 10.0%, 3.9% in 12-15 yr olds, respectively. For allergic conjunctivitis, food allergy, and drug allergy, the prevalences in 6-12 yr olds were 11.2%, 6.5%, and 1.5%, respectively. Asthma and flexural eczema decreased significantly with age. Other significant risk factors were also noted. For 6-12 yr-old asthma, adjusted odds ratio (aOR) of body mass index was 1.21 with 95% confidence interval (CI) 1.0-1.48, aOR of passive smoking was 1.37 with 95%CI 1.24-1.51, aOR of carpet use was 1.28 with 95%CI 1.10-1.49. For 6-12 yr-old eczema, aOR of affluence was 1.22 with 95%CI 1.07-1.39. The control of obesity and passive smoking would be the most important preventive measures of allergic diseases.
Importance Understanding birth cohort–specific tobacco smoking patterns and their association with total and cause-specific mortality is important for projecting future deaths due to tobacco smoking across Asian populations. Objectives To assess secular trends of tobacco smoking by countries or regions and birth cohorts and evaluate the consequent mortality in Asian populations. Design, Setting, and Participants This pooled meta-analysis was based on individual participant data from 20 prospective cohort studies participating in the Asia Cohort Consortium. Between September 1, 2017, and March 31, 2018, a total of 1 002 258 Asian individuals 35 years or older were analyzed using Cox proportional hazards regression analysis and random-effects meta-analysis. The pooled results were presented for mainland China; Japan; Korea, Singapore, and Taiwan; and India. Exposures Tobacco use status, age at starting smoking, number of cigarettes smoked per day, and age at quitting smoking. Main Outcomes and Measures Country or region and birth cohort–specific mortality and the population attributable risk for deaths from all causes and from lung cancer. Results Of 1 002 258 participants (51.1% women and 48.9% men; mean [SD] age at baseline, 54.6 [10.4] years), 144 366 deaths (9158 deaths from lung cancer) were ascertained during a mean (SD) follow-up of 11.7 (5.3) years. Smoking prevalence for men steadily increased in China and India, whereas it plateaued in Japan and Korea, Singapore, and Taiwan. Among Asian male smokers, the mean age at starting smoking decreased in successive birth cohorts, while the mean number of cigarettes smoked per day increased. These changes were associated with an increasing relative risk of death in association with current smoking in successive birth cohorts of pre-1920, 1920s, and 1930 or later, with hazard ratios for all-cause mortality of 1.26 (95% CI, 1.17-1.37) for the pre-1920 birth cohort, 1.47 (95% CI, 1.35-1.61) for the 1920s birth cohort, and 1.70 (95% CI, 1.57-1.84) for the cohort born in 1930 or later. The hazard ratios for lung cancer mortality were 3.38 (95% CI, 2.25-5.07) for the pre-1920 birth cohort, 4.74 (95% CI, 3.56-6.32) for the 1920s birth cohort, and 4.80 (95% CI, 3.71-6.19) for the cohort born in 1930 or later. Tobacco smoking accounted for 12.5% (95% CI, 8.4%-16.3%) of all-cause mortality in the pre-1920 birth cohort, 21.1% (95% CI, 17.3%-24.9%) of all-cause mortality in the 1920s birth cohort, and 29.3% (95% CI, 26.0%-32.3%) of all-cause mortality for the cohort born in 1930 or later. Tobacco smoking among men accounted for 56.6% (95% CI, 44.7%-66.3%) of lung cancer mortality in the pre-1920 birth cohort, 66.6% (95% CI, 58.3%-73.5%) of lung cancer mortality in the 1920s birth cohort, and 68.4% (95% CI, 61.3%-74.4%) of lung cancer mortality for the cohort born in 1930 or later. For women, tobacco smoking patterns an...
Key Points Question What is the association between diabetes and mortality in Asian populations? Findings In this pooled analysis of data from more than 1 million individual participants of 22 studies in Asia, diabetes was associated with substantially increased risk of death from a broad spectrum of diseases, particularly diabetes itself, renal disease, coronary heart disease, and ischemic stroke. The associations were more evident among women and younger patients than among men and elderly patients. Meaning The study’s findings suggest the urgent need for developing diabetes management programs that are tailored to Asian populations and the subsequent strong implementation of these programs in Asia.
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