To enhance user perceived performance,Akamai' s content distribution network(CDN) utilizes the domain name system(DNS) effectively to redirect users to close-by content replicas over short time scale.The use of DN...To enhance user perceived performance,Akamai' s content distribution network(CDN) utilizes the domain name system(DNS) effectively to redirect users to close-by content replicas over short time scale.The use of DNS redirection has brought a significant advantage to Akamai' s CDN.However,the reliance on DNS also poses a fundamental threat to Akamai' s content distribution model.In particular,systematic evaluation and quantification illustrates the impact of recent emerging public DNS resolving services on Akamai' s CDN,including the degradation of corresponding user perceived performance and the benefit damnification of collaborating internet services providers(ISPs) that host Akamai's edge servers.The measurement demonstrates that a considerable penetration of public DNS resolving services(e.g.,OpenDNS and GoogleDNS) effectively corrupts the Akamai' s serving model,namely the large-scale server distribution and quick DNS redirection.展开更多
With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high...With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high-performance video streams over 802.11 WLANs remains a challenging task due to the inherent characteristics of compressed video and dynamic channels. In this paper, we present a brief survey of various recent innovations that have been developed to enhance the Quality of Service (QoS) performance for video over WLANs. Based on the application scenarios, the solutions have focused mainly on three network layers, that is, Application layer (APP), Media Access Control layer (MAC), and Physical layer (PHY). After reviewing the video compression technology, we first examine various single-layer solutions for video over WLANs. We then discuss several cross-layer solutions that take advantage of mutual interactions between different network layers. Finally, several technical issues beyond QoS performance, including energy and security, are also addressed. We conclude that the application of video over WLANs will continue to increase in future.展开更多
This review study was designed to map out the research trends through an intensive text analysis of 1,366 research articles （RAs） of applied linguistics during the past 40 years （from 1976 to 2015）. RAs were coded...This review study was designed to map out the research trends through an intensive text analysis of 1,366 research articles （RAs） of applied linguistics during the past 40 years （from 1976 to 2015）. RAs were coded and analyzed by four analysts to identify their content of research, research methods, and statistical procedures. It was found that there has been an increase in the number and the average length of articles. The average length has been on the rise from 8.09 pages in 1976-1985 to 14.38 during 2006-2015. The extensive review of the RAs also revealed a broad range of themes that belonged to 34 research domains. SLA, Technology 8： Language Learning, Language Teaching Methodology, Language Testing, and Psycholinguistics were the most widely researched areas. The qualitative method with 33.97% was the dominant research method in the journals. Regarding the statistical techniques, it was illustrated that descriptive statistics, Pearson correlation, ANOVA, and t-test were the most commonly used procedures in the applied linguistic RAs.展开更多
基金Supported by the National Basic Research Program of China(No.2013CB329103)the National Natural Science Foundation of China(No.61133016,61300191)+1 种基金the National High Technology Joint Research Program of China(No.2011AA010706)the Program of SichuanProvince Applied and Basic Research(No.2013JY0116)
文摘To enhance user perceived performance,Akamai' s content distribution network(CDN) utilizes the domain name system(DNS) effectively to redirect users to close-by content replicas over short time scale.The use of DNS redirection has brought a significant advantage to Akamai' s CDN.However,the reliance on DNS also poses a fundamental threat to Akamai' s content distribution model.In particular,systematic evaluation and quantification illustrates the impact of recent emerging public DNS resolving services on Akamai' s CDN,including the degradation of corresponding user perceived performance and the benefit damnification of collaborating internet services providers(ISPs) that host Akamai's edge servers.The measurement demonstrates that a considerable penetration of public DNS resolving services(e.g.,OpenDNS and GoogleDNS) effectively corrupts the Akamai' s serving model,namely the large-scale server distribution and quick DNS redirection.
文摘With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high-performance video streams over 802.11 WLANs remains a challenging task due to the inherent characteristics of compressed video and dynamic channels. In this paper, we present a brief survey of various recent innovations that have been developed to enhance the Quality of Service (QoS) performance for video over WLANs. Based on the application scenarios, the solutions have focused mainly on three network layers, that is, Application layer (APP), Media Access Control layer (MAC), and Physical layer (PHY). After reviewing the video compression technology, we first examine various single-layer solutions for video over WLANs. We then discuss several cross-layer solutions that take advantage of mutual interactions between different network layers. Finally, several technical issues beyond QoS performance, including energy and security, are also addressed. We conclude that the application of video over WLANs will continue to increase in future.
文摘This review study was designed to map out the research trends through an intensive text analysis of 1,366 research articles （RAs） of applied linguistics during the past 40 years （from 1976 to 2015）. RAs were coded and analyzed by four analysts to identify their content of research, research methods, and statistical procedures. It was found that there has been an increase in the number and the average length of articles. The average length has been on the rise from 8.09 pages in 1976-1985 to 14.38 during 2006-2015. The extensive review of the RAs also revealed a broad range of themes that belonged to 34 research domains. SLA, Technology 8： Language Learning, Language Teaching Methodology, Language Testing, and Psycholinguistics were the most widely researched areas. The qualitative method with 33.97% was the dominant research method in the journals. Regarding the statistical techniques, it was illustrated that descriptive statistics, Pearson correlation, ANOVA, and t-test were the most commonly used procedures in the applied linguistic RAs.
