Improved group-based cooperative caching scheme for mobile ad hoc networks

Data caching is a popular technique that improves data accessibility in wired or wireless networks. However, in mobile ad hoc networks, improvement in access latency and cache hit ratio may diminish because of the mobility and limited cache space of mobile hosts (MHs). In this paper, an improved cooperative caching scheme called group-based cooperative caching (GCC) is proposed to generalize and enhance the performance of most group-based caching schemes. GCC allows MHs and their neighbors to form a group, and exchange a bitmap data directory periodically used for proposed algorithms, such as the process of data discovery, and cache placement and replacement. The goal is to reduce the access latency of data requests and efficiently use available caching space among MH groups. Two optimization techniques are also developed for GCC to reduce computation and communication overheads. The first technique compresses the directories using an aggregate bitmap. The second employs multi-point relays to develop a forwarding node selection scheme to reduce the number of broadcast messages inside the group. Our simulation results show that the optimized GCC yields better results than existing cooperative caching schemes in terms of cache hit ratio, access latency, and average hop count.     

A generalized target-driven cache replacement policy for mobile environments

Caching frequently accessed data items on the client side is an effective technique to improve the system performance in wireless networks. Due to cache size limitations, cache replacement algorithms are used to find a suitable subset of items for eviction from the cache. Many existing cache replacement algorithms employ a value function of different factors such as time since last access, entry time of the item in the cache, transfer time, item expiration time and so on. However, most of the existing algorithms are designed for WWW environment under weak consistency model. Their choices of value functions are based on experience and on a value function which only works for a specific performance metric.In this paper, we propose a generalized value function for cache replacement algorithms for wireless networks under a strong consistency model. The distinctive feature of our value function is that it is generalized and can be used for various performance metrics by making the necessary changes. Further, we prove that the proposed value function can optimize the access cost in our system model. To demonstrate the practical effectiveness of the generalized value function, we derive two specific functions and evaluate them by setting up two different targets: minimizing the query delay and minimizing the downlink traffic. Compared to previous schemes, our algorithm significantly improves the performance in terms of query delay or in terms of bandwidth utilization depending on the specified target.     

Gossip-based cooperative caching for mobile applications in mobile wireless networks

Cooperative caching is an efficient way to improve the performance of data access in mobile wireless networks, by cache nodes selecting different data items in their limited storage in order to reduce total access delay. With more demands on sharing a video or other data, especially for mobile applications in an Internet-based Mobile Ad Hoc Network, considering the relations among data items in cooperative caching becomes more important than before. However, most of the existing works do not consider these inherent relations among data items, such as the logical, temporal, or spatial relations. In this paper, we present a novel solution, Gossip-based Cooperative Caching (GosCC) to address the cache placement problem, and consider the sequential relation among data items. Each mobile node stores the IDs of data items cached locally and the ID of the data item in use into its progress report. Each mobile node also makes use of these progress reports to determine whether a data item should be cached locally. These progress reports are propagated within the network in a gossip-based way. To improve the user experience, GosCC aims to provide users with an uninterrupted data access service. Simulation results show that GosCC achieves better performance than Benefit-based Data Caching and HybridCache, in terms of average interruption intervals and average interruption times, while sacrificing message cost to a certain degree.     

内容中心移动边缘网络用户移动感知缓存机制

为了提高内容中心移动边缘网络的缓存性能,提出了一种基于用户移动性感知和节点中心性度量的内容中心移动边缘网络缓存机制（user mobility-aware and node centrality based caching,简称UMANCC）.UMANCC机制利用边缘节点计算节点中心性、缓存空闲率以及小区内用户逗留时间.移动边缘网络控制器综合各边缘节点的信息,计算各边缘节点的重要性并进行排序,最后根据排序结果选择内容缓存节点.仿真实验结果表明：与传统缓存机制LCE及Prob相比,UMANCC有效减少用户获取内容的平均跳数高达15.9%,提高边缘节点缓存命中率至少13.7%,减少进入核心网流量高达32.1%,有效地提高了内容中心移动边缘网络的内容分发性能.     

无线Web访问的缓存和预取机制

缓存和预取在提高无线环境下的Web访问性能方面发挥着重要作用。文章研究针对无线局域网的Web缓存和预取机制,分别基于数据挖掘和信息论提出了采用序列挖掘和延迟更新的预测算法,设计了上下文感知的预取算法和获益驱动的缓存替换机制,上述算法已在Web缓存系统OnceEasyCache中实现。性能评估实验结果表明,上述算法的集成能有效地提高缓存命中率和延迟节省率。     

CCN中基于业务分类和节点分区的混合缓存机制

针对内容中心网络(content centric networking,CCN)中不同业务内容的合理放置问题,提出了一种基于业务分类和节点分区的混合缓存机制。根据不同的业务特征,设计了差异化的缓存策略。对于流媒体点播业务,采用基于流行度的推拉式缓存,实现其在边缘网络的按序存储;对于非流媒体共享内容,采用基于hash的显式缓存,实现其在核心网络的单一副本放置。仿真结果表明,与经典算法相比,该机制提高了缓存命中率和跳数减少率,降低了平均请求时延。     

Proxy cache algorithms: design, implementation, and performance

Caching at proxy servers is one of the ways to reduce the response time perceived by World Wide Web users. Cache replacement algorithms play a central role in the response time reduction by selecting a subset of documents for caching, so that a given performance metric is maximized. At the same time, the cache must take extra steps to guarantee some form of consistency of the cached documents. Cache consistency algorithms enforce appropriate guarantees about the staleness of the cached documents. We describe a unified cache maintenance algorithm, LNC-R-WS-U, which integrates both cache replacement and consistency algorithms. The LNC-R-WS-U algorithm evicts documents from the cache based on the delay to fetch each document into the cache. Consequently, the documents that took a long time to fetch are preferentially kept in the cache. The LNC-R-W3-U algorithm also considers in the eviction consideration the validation rate of each document, as provided by the cache consistency component of LNC-R-WS-U. Consequently, documents that are infrequently updated and thus seldom require validations are preferentially retained in the cache. We describe the implementation of LNC-R-W3-U and its integration with the Apache 1.2.6 code base. Finally, we present a trace-driven experimental study of LNC-R-W3-U performance and its comparison with other previously published algorithms for cache maintenance     

移动自组网DSR协议路径缓存策略优化

移动自组网按需机制路由协议只是在有分组发送时,才启动路径发现机制搜索到达目的节点的路径。为了避免每发送一个分组都启动路由发现机制,必须利用路由保存机制将预先发现的路径缓存。对这些路径进行缓存、搜索、抛弃的管理策略极大地影响按需机制路由协议的性能。该文对多次性能测试中表现优越的DSR协议路由缓存策略进行分析,针对它的不足,提出改进算法。提出修正发送缓冲器的时限,根据最近路径失效时间和缓冲器中路径状况预测将来的路径失效时间,在缓存器中根据时间、能量参数搜索最佳路径、丢弃最差路径的策略。利用ns2对4组场景进行仿真,结果显示对DSR路径缓存策略进行优化后,比较明显改进了DSR协议性能。     

Dynamic Partitioning and Popularity based Caching for Optimized Performance in content-centric fog networks: DPPCOP

With the massive growth of information generation, processing, and distribution in the Internet of Things (IoT), the existing cloud architectures need to be designed more effectively using fog networks. The current IP-address-based Internet architecture is unable to deliver the desired Quality-of-Service (QoS) towards the increasing demands of fog networking-based applications. To this end, Content-Centric Networking (CCN) has been developed as the potential future Internet architecture. CCN provides name-based content delivery and is established as an architecture for next-generation fog applications. The CCN-based fog environment uses the cache of in-network fog nodes to place the contents near the end-user devices. Generally, the caching capacity of the fog nodes is very small as compared to the content catalog size. Therefore, efficient content placement decisions are vital for improving the network performance. To enhance the content retrieval performance for the end-users, a novel content caching scheme named “Dynamic Partitioning and Popularity based Caching for Optimized Performance (DPPCOP)” has been proposed in this paper. First, the proposed scheme partitions the fog network by grouping the fog nodes into non-overlapping partitions to improve content distributions in the network and to ensure efficient content placement decisions. During partitioning, the scheme uses the Elbow method to obtain the “good” number of partitions. Then, the DPPCOP scheme analyzes the partition’s information along with the content popularity and distance metrics to place the popular contents near the end-user devices. Extensive simulations on realistic network topologies demonstrate the superiority of the DPPCOP caching strategy on existing schemes over various performance measurement parameters such as cache hit ratio, delay, and average network traffic load. This makes the proposed scheme suitable for next-generation CCN-based fog networks and the futuristic Internet architectures for industry 4.0.     

无线Mesh网络中节点分级协作缓冲机制研究

在无线Mesh中,由于每个节点缓冲的数据量不同,可能会造成某些节点的缓冲区利用率低,某些节点因为缓冲任务繁重而进行频繁的数据置换操作,从而造成节点存储空间使用不均衡,降低数据缓冲的效率。提出了一种基于节点分级管理的协作缓冲算法,该算法为网络中的每个节点在网络中构造一个分布式缓冲区域,利用该缓冲区域来替代节点本身的缓冲区,通过合理地利用每个节点的存储空间,增加单个节点的数据缓冲能力。理论分析和实验结果表明,该算法可以有效提高数据访问命中率,减少缓冲区数据的置换操作,降低节点的能量消耗。     

动态无线传感网中低延迟高可靠的数据查询机制

查询处理作为大规模无线传感器网络中智能服务的一个重要操作,可以根据用户需求对网络中的感知数据进行检索和回传.然而,部署在恶劣环境中的无线传感网络,节点容易遭受外力破坏,或者自身资源(能量、存储等)有限,可能会导致节点发生位移和故障,从而造成网络拓扑不断改变以及部分节点的感知数据失效.同时,由于节点感知数据容量大、传输带宽有限以及网络链路不可靠等情况,可能会造成网络通信时延大大增加.这些因素使得快速、可靠的数据查询处理成为无线传感网中一个难题.为了解决这个难题,提出一种动态网络中低延迟高可靠的数据查询机制.该机制是一种非聚合随机查询方式,通过将传感节点划分为源节点和查询节点来实现数据查询.首先,根据监测事件将网络划分为若干个子区域,每个子区域中的源节点相互协作,并按照时间顺序依次轮流监听该区域的事件信息;接着,源节点根据预估的平均节点故障概率,计算出一个合理的备份数量,并将源数据按照该数量存储到邻居节点中,以降低源数据的失效概率;然后,为了加快数据查询速度,源节点定期对源数据块进行编码压缩,并选取剩余能量和存储空间较小的多个邻居节点作为下一跳接收节点.这些接收节点基于局部区域中节点个数大小,决定是否接收存储该报文.重复上述过程,直至压缩数据均匀地分布在网络中.另一方面,查询节点接收到查询请求时,也使用负载均衡多路分发方式将查询请求传输到部分节点上.为了避免目标数据的冗余回传,当查询请求成功查询到目标数据时,目标节点先修改访问位,再选取与查询节点距离最近的邻居节点作为下一跳接收节点,迭代执行上述操作,直到用户获得所需要的事件信息.在以上过程中,为了节省节点能量,在保证高成功查询率的条件下,建立通信能耗最小化的优化模型,计算出最优的压缩数据副本数和查询消息副本数,之后,源节点和查询节点分别按照该数量进行副本数据分发.最后,理论分析和实验结果表明,与其它四种查询算法相比,提出的查询机制具有更高的查询成功率、更低的通信能耗和通信时延.     

一种空间信息网络缓存决策策略

针对空间信息网络（space information network,SIN）中卫星节点缓存容量有限,且卫星高速移动使得星间链路时变,导致地面用户内容访问延迟增大的问题,提出一种基于人工蜂群算法的空间信息网络缓存决策策略（satellite improved artificial bee colony,SIABC）。首先根据低轨卫星节点链路切换的周期性和可预知性,建立网络分区模型,对空间信息网络的卫星节点进行分区,在此基础上,建立区域节点协作缓存模型,使得整个网络区域内的卫星节点有选择性地缓存不同流行度的内容,同时兼顾区域内节点的协作缓存,从而流行度高的内容缓存在网络边缘。仿真结果表明,与现有缓存机制相比,该缓存策略能够明显提高内容的平均缓存命中率,并显著降低用户的内容访问时延。     

Distributed caching in unstructured peer-to-peer file sharing networks

Nowadays, the peer-to-peer (P2P) system is one of the largest Internet bandwidth consumers. To relieve the burden on Internet backbone and improve the query and retrieve performance of P2P file sharing networks, efficient P2P caching algorithms are of great importance. In this paper, we propose a distributed topology-aware unstructured P2P file caching infrastructure and design novel placement and replacement algorithms to achieve optimal performance. In our system, for each file, an adequate number of copies are generated and disseminated at topologically distant locations. Unlike general believes, our caching decisions are in favor of less popular files. Combined with the underlying topology-aware infrastructure, our strategy retains excellent performance for popular objects while greatly improves the caching performance for less popular files. Overall, our solution can reduce P2P traffic on Internet backbone, and relieve the over-caching problem that has not been properly addressed in unstructured P2P networks. We carry out simulation experiments to compare our approaches with several traditional caching strategies. The results show that our algorithms can achieve better query hit rates, smaller query delay, higher cache hit rates, and lower communication overhead.     

Performance evaluations of data-centric information retrieval schemes for DTNs

Mobile nodes in some challenging network scenarios, e.g. battlefield and disaster recovery scenarios, suffer from intermittent connectivity and frequent partitions. Disruption Tolerant Network (DTN) technologies are designed to enable communications in such environments. Several DTN routing schemes have been proposed. However, not much work has been done on designing schemes that provide efficient information access in such challenging network scenarios. In this paper, we explore how a content-based information retrieval system can be designed for DTNs. There are three important design issues, namely (a) how data should be replicated and stored at multiple nodes, (b) how a query is disseminated in sparsely connected networks, and (c) how a query response is routed back to the issuing node. We first describe how to select nodes for storing the replicated copies of data items. We consider the random and the intelligent caching schemes. In the random caching scheme, nodes that are encountered first by a data-generating node are selected to cache the extra copies while in the intelligent caching scheme, nodes that can potentially meet more nodes, e.g. faster nodes, are selected to cache the extra data copies. The number of replicated data copies K can be the same for all data items or varied depending on the access frequencies of the data items. In this work, we consider fixed, proportional and square-root replication schemes. Then, we describe two query dissemination schemes: (a) W-copy Selective Query Spraying (WSS) scheme and (b) L-hop Neighborhood Spraying (LNS) scheme. In the WSS scheme, nodes that can move faster are selected to cache the queries while in the LNS scheme, nodes that are within L-hops of a querying node will cache the queries. For message routing, we use an enhanced Prophet scheme where a next-hop node is selected only if its predicted delivery probability to the destination is higher than a certain threshold. We conduct extensive simulation studies to evaluate different combinations of the replication and query dissemination algorithms. Our results reveal that the scheme that performs the best is the one that uses the WSS scheme combined with binary spread of replicated data copies. The WSS scheme can achieve a higher query success ratio when compared to a scheme that does not use any data and query replication. Furthermore, the square-root and proportional replication schemes provide higher query success ratio than the fixed copy approach with varying node density. In addition, the intelligent caching approach can further improve the query success ratio by 5.3–15.8% with varying node density. Our results using different mobility models reveal that the query success ratio degrades at most 7.3% when the Community-Based model is used compared to the Random Waypoint (RWP) model [J. Broch et al., A Performance Comparison of Multihop wireless Ad hoc Network Routing Protocols, ACM Mobicom, 1998, pp. 85–97]. Compared to the RWP and the Community-Based mobility models, the UmassBusNet model from the DieselNet project [X. Zhang et al., Modeling of a Bus-based Disruption Tolerant Network Trace, Proceedings of ACM Mobihoc, 2007.] achieves much lower query success ratio because of the longer inter-node encounter time.     

A cache invalidation strategy for mobile networks

The diversity of services delivered over wireless channels has increased people's desire in ubiquitously accessing these services from their mobile devices. However, a ubiquitous mobile computing environment faces several challenges such as scarce bandwidth, limited energy resources, and frequent disconnection of the server and mobile devices. Caching frequently accessed data is an effective technique to improve the network performance because it reduces the network congestion, the query delay, and the power consumption. When caching is used, maintaining cache consistency becomes a major challenge since data items that are updated on the server should be also updated in the cache of the mobile devices. In this paper we propose a new cache invalidation scheme called Selective Adaptive Sorted (SAS) cache invalidation strategy that overcomes the false invalidation problem that exists in most of the invalidation strategies found in the literature. The performance of the proposed strategy is evaluated and compared with the selective cache invalidation strategy and the updated invalidation report startegy found in the literature. Results showed that a significant cost reduction can be obtained with the proposed strategy when measuring performance metrics such as delay, bandwidth, and energy.     

无线网络环境下的缓存策略研究

日益普及的无线网络和移动设备为普适的Internet接入提供了良好的硬件基础,缓存技术是普适Internet场景中人们进行信息共享和分发的关键技术之一.综述了两类无线网络环境,即基于基础设施无线网络环境和移动自组网中的缓存策略,具体包括缓存放置策略、缓存替换策略、缓存一致性维护算法.进而分析、讨论了上述策略的优缺点,并指出了缓存策略的发展趋势.     

机会网络节点协作缓存策略设计与实现

针对如何有效利用机会网络中节点间的协作关系以及节点有限的缓存资源,避免拥塞和提升数据传输性能的问题,提出一种机会网络协作缓存优化策略——HMP-Cache。该策略根据节点不同运动状态的特点,利用目标地址匹配标准选择协作缓存节点,采用同步Cache数据表达到局部域内缓存信息共享的目的。仿真实验结果表明,该策略能够有效控制数据访问的网络开销,降低网络热点数据访问延迟。     

Energy-Efficient Mobile Cache Invalidation

Caching data in a wireless mobile computer can significantly reduce the bandwidth requirement. However, due to battery power limitation, a wireless mobile computer may often be forced to operate in a doze or even totally disconnected mode. As a result, the mobile computer may miss some cache invalidation reports. In this paper, we present an energy-efficient cache invalidation method for a wireless mobile computer. The new cache invalidation scheme is called grouping with cold update-set retention (GCORE). Upon waking up, a mobile computer checks its cache validity with the server. To reduce the bandwidth requirement for validity checking, data objects are partitioned into groups. However, instead of simply invalidating a group if any of the objects in the group has been updated, GCORE retains the cold update set of objects in a group if possible. We present an efficient implementation of GCORE and conduct simulations to evaluate its caching effectiveness. The results show that GCORE can substantially improve mobile caching by reducing the communication bandwidth (thus energy consumption) for query processing.     

内容中心网络中基于区域集中化控制的协作缓存路由机制*

针对在内容中心网络(Content Centric Networking, CCN)中如何合理放置与高效利用应答数据的问题,该文将集中化控制的思想引入到内容缓存与查找中,提出一种协作缓存路由机制。缓存决策时,通过兴趣包和数据包携带标签的方式,确定沿途最大缓存收益区域;在最大缓存收益区域内,结合内容全局活跃度和节点可用缓存空间,选择内容最佳放置位置。路由查找时,将区域内容放置与路由转发相结合,增大缓存资源可用性。仿真结果表明,与经典算法相比,该机制以少量额外的开销提高了缓存命中率和跳数减少率,改善了缓存负载分布均衡性,提升了CCN网络缓存和传输效率。     

An Efcient Hop Count Routing Protocol for Wireless Ad Hoc Networks

An efcient hop count route fnding approach for mobile ad hoc network is presented in this paper.It is an adaptive routing protocol that has a tradeof between transmission power and hop count for wireless ad hoc networks.During the route fnding process,the node can dynamically assign transmission power to nodes along the route.The node who has received route request message compares its power with the threshold power value,and then selects a reasonable route according to discriminating algorithms.This algorithm is an efective solution scheme to wireless ad hoc networks through reasonably selected path to reduce network consumption.Simulation results indicate that the proposed protocol can deliver better performances with respect to energy consumption and end-to-end delay.