The moisture content of dead forest fuel is an important indicator of risk levels of forest fires and prediction of fire spread. Moisture distribution is important to determine wild fire rating. However, it is often d...The moisture content of dead forest fuel is an important indicator of risk levels of forest fires and prediction of fire spread. Moisture distribution is important to determine wild fire rating. However, it is often difficult to predict moisture distribution because of a complex terrain, changeable environments and low cover of commercial communication signals inside the forest. This study proposes a moisture content prediction system composed of environmental data collected using a long range radio frequency band 433 MHz wireless sensor network and data processing for moisture prediction based on a BP (back-propagation) neural network. In the fall of 2019, twenty nodes for the collection of environmental data were placed in four forest stands of Maoershan National Forest for a month;7440 sets of data including temperature, humidity, wind speed and air pressure were obtained. Half the data were used as a training set, the other as a testing set for a BP neural network. The results show that the average absolute error between the predicted value and the real value of moisture content of fuels of Larix gmelini, Betula platyphylla, Juglans mandshurica, and Quercus mongolica stands was 0.94%, 0.21%, 0.86%, 0.97%, respectively. The prediction accuracy was relatively high. The proposed distributed moisture content prediction method has the advantages of wide coverage and good real-time performance;at the same time, it is not limited by commercial signals and so it is especially suitable for forest fire prediction in remote mountainous areas.展开更多
Peer-to-Peer (P2P) networks are highly dynamic systems which are very popular for content distribution in the Internet. A single peer remains in the system for an unpredictable amount of time, and the rate in which pe...Peer-to-Peer (P2P) networks are highly dynamic systems which are very popular for content distribution in the Internet. A single peer remains in the system for an unpredictable amount of time, and the rate in which peers enter and leave the system, i.e. the churn, is often high. A user that is obtaining content from a selected peer is frequently informed that particular peer is not available anymore, and is asked to select another peer, or will have another peer assigned, often without enough checks to confirm that the content provided by the new peer presents the same quality of the previous peer. In this work we present a strategy based on group communication for transparent and robust content access in P2P networks. Instead of accessing a single peer for obtaining the desired content, a user request is received and processed by a group of peers. This group of peers, called PCG (Peer Content Group) provides reliable content access in sense that even as members of the group crash or leave the system, users continue to receive the content if at least one group member remains fault-free. Each PCG member is capable of independently serving the request. A PCG is transparent to the user, as the group interface is identical to the interface provided by a single peer. A group member is elected to serve each request. A fault monitoring component allows the detection of member crashes. If the peer is serving request crashes, another group member is elected to continue providing the service. The PCG and a P2P file sharing applications were implemented in the JXTA platform. Evaluation results are presented showing the latency of group operations and system components.展开更多
随着互联网技术的发展和普及,广播电视流媒体传输已经成为人们获取信息和娱乐的重要方式之一。然而由于网络环境的复杂性和不稳定性,如何保证流媒体传输的质量成一个重要的问题。内容分发网络(Content Distribution Network,CDN)作为一...随着互联网技术的发展和普及,广播电视流媒体传输已经成为人们获取信息和娱乐的重要方式之一。然而由于网络环境的复杂性和不稳定性,如何保证流媒体传输的质量成一个重要的问题。内容分发网络(Content Distribution Network,CDN)作为一种有效的解决方案被广泛应用于流媒体传输。为优化传输质量、提高用户体验,探讨基于CDN的广播电视流媒体传输质量优化方法。展开更多
Information-Centric Networking(ICN), an alternative architecture to the current Internet infrastructure, focuses on the distribution and retrieval of content by employing caches in a network to reduce network traffic....Information-Centric Networking(ICN), an alternative architecture to the current Internet infrastructure, focuses on the distribution and retrieval of content by employing caches in a network to reduce network traffic. The employment of caches may be accomplished using graph-based and content-based criteria such as the position of a node in a network and content popularity. The contribution of this paper lies on the characterization of content popularity for on-path in-network caching. To this end, four dynamic approaches for identifying content popularity are evaluated via simulations. Content popularity may be determined per chunk or per object, calculated by the number of requests for a content against the sum of requests or the maximum number of requests. Based on the results, chunk-based approaches provide 23% more accurate content popularity calculations than object-based approaches. In addition, approaches that are based on the comparison of a content against the maximum number of requests have been shown to be more accurate than the alternatives.展开更多
为了提供高质量的流媒体服务,内容发布网络(CDN)利用域名解析系统(DNS),将用户重定向到附近的内容服务器。近年来,域名解析系统的发展,尤其是基于IPAnycast的域名解析系统的兴起(例如,Google Public DNS,Open DNS),必将对CDN网络的内容...为了提供高质量的流媒体服务,内容发布网络(CDN)利用域名解析系统(DNS),将用户重定向到附近的内容服务器。近年来,域名解析系统的发展,尤其是基于IPAnycast的域名解析系统的兴起(例如,Google Public DNS,Open DNS),必将对CDN网络的内容发布机制造成影响。同Web、Email等其它Internet服务相比,流媒体服务对网络资源有较高的要求,DNS对其影响更加明显。本文首先阐明基于IPAnycast的域名解析系统对CDN网络内容发布模型的冲击,然后分析其影响流媒体服务质量的各种因素,最后通过实验来比较当使用不同域名解析服务时CDN网络承载的流媒体的服务质量。展开更多
基金This work was supported by the Fundamental Research Funds for the Central Universities(Grant No.2572020AW43NO.2572019CP19)+2 种基金the National Natural Science Foundation of China(Grant No.31470715)the Natural Science Foundation of Hei-longjiang Province(Grant No.TD2020C001)the project for cultivating excellent doctoral dissertation of forestry engineering(Grant No.LYGCYB202009).
文摘The moisture content of dead forest fuel is an important indicator of risk levels of forest fires and prediction of fire spread. Moisture distribution is important to determine wild fire rating. However, it is often difficult to predict moisture distribution because of a complex terrain, changeable environments and low cover of commercial communication signals inside the forest. This study proposes a moisture content prediction system composed of environmental data collected using a long range radio frequency band 433 MHz wireless sensor network and data processing for moisture prediction based on a BP (back-propagation) neural network. In the fall of 2019, twenty nodes for the collection of environmental data were placed in four forest stands of Maoershan National Forest for a month;7440 sets of data including temperature, humidity, wind speed and air pressure were obtained. Half the data were used as a training set, the other as a testing set for a BP neural network. The results show that the average absolute error between the predicted value and the real value of moisture content of fuels of Larix gmelini, Betula platyphylla, Juglans mandshurica, and Quercus mongolica stands was 0.94%, 0.21%, 0.86%, 0.97%, respectively. The prediction accuracy was relatively high. The proposed distributed moisture content prediction method has the advantages of wide coverage and good real-time performance;at the same time, it is not limited by commercial signals and so it is especially suitable for forest fire prediction in remote mountainous areas.
文摘Peer-to-Peer (P2P) networks are highly dynamic systems which are very popular for content distribution in the Internet. A single peer remains in the system for an unpredictable amount of time, and the rate in which peers enter and leave the system, i.e. the churn, is often high. A user that is obtaining content from a selected peer is frequently informed that particular peer is not available anymore, and is asked to select another peer, or will have another peer assigned, often without enough checks to confirm that the content provided by the new peer presents the same quality of the previous peer. In this work we present a strategy based on group communication for transparent and robust content access in P2P networks. Instead of accessing a single peer for obtaining the desired content, a user request is received and processed by a group of peers. This group of peers, called PCG (Peer Content Group) provides reliable content access in sense that even as members of the group crash or leave the system, users continue to receive the content if at least one group member remains fault-free. Each PCG member is capable of independently serving the request. A PCG is transparent to the user, as the group interface is identical to the interface provided by a single peer. A group member is elected to serve each request. A fault monitoring component allows the detection of member crashes. If the peer is serving request crashes, another group member is elected to continue providing the service. The PCG and a P2P file sharing applications were implemented in the JXTA platform. Evaluation results are presented showing the latency of group operations and system components.
文摘随着互联网技术的发展和普及,广播电视流媒体传输已经成为人们获取信息和娱乐的重要方式之一。然而由于网络环境的复杂性和不稳定性,如何保证流媒体传输的质量成一个重要的问题。内容分发网络(Content Distribution Network,CDN)作为一种有效的解决方案被广泛应用于流媒体传输。为优化传输质量、提高用户体验,探讨基于CDN的广播电视流媒体传输质量优化方法。
基金funded by the Higher Education Authority (HEA)co-funded under the European Regional Development Fund (ERDF)
文摘Information-Centric Networking(ICN), an alternative architecture to the current Internet infrastructure, focuses on the distribution and retrieval of content by employing caches in a network to reduce network traffic. The employment of caches may be accomplished using graph-based and content-based criteria such as the position of a node in a network and content popularity. The contribution of this paper lies on the characterization of content popularity for on-path in-network caching. To this end, four dynamic approaches for identifying content popularity are evaluated via simulations. Content popularity may be determined per chunk or per object, calculated by the number of requests for a content against the sum of requests or the maximum number of requests. Based on the results, chunk-based approaches provide 23% more accurate content popularity calculations than object-based approaches. In addition, approaches that are based on the comparison of a content against the maximum number of requests have been shown to be more accurate than the alternatives.
文摘为了提供高质量的流媒体服务,内容发布网络(CDN)利用域名解析系统(DNS),将用户重定向到附近的内容服务器。近年来,域名解析系统的发展,尤其是基于IPAnycast的域名解析系统的兴起(例如,Google Public DNS,Open DNS),必将对CDN网络的内容发布机制造成影响。同Web、Email等其它Internet服务相比,流媒体服务对网络资源有较高的要求,DNS对其影响更加明显。本文首先阐明基于IPAnycast的域名解析系统对CDN网络内容发布模型的冲击,然后分析其影响流媒体服务质量的各种因素,最后通过实验来比较当使用不同域名解析服务时CDN网络承载的流媒体的服务质量。
