22-10-2011, 09:52 PM
Check out the attachment for review document for Caching Strategies Based on Information Density Estimation in Wireless Ad Hoc Networks, IEEE 2011 JAVA PROJECT
22-10-2011, 09:52 PM
Check out the attachment for review document for Caching Strategies Based on Information Density Estimation in Wireless Ad Hoc Networks, IEEE 2011 JAVA PROJECT
17-03-2012, 02:47 PM
25-03-2012, 11:01 AM
what is the methodology used in this project?pls send the report of methodology.
18-02-2013, 10:18 AM
Caching Strategies Based on Information Density Estimation in Wireless Ad Hoc Networks
Caching Strategies.pdf (Size: 1.12 MB / Downloads: 28) Abstract We address cooperative caching in wireless networks, where the nodes may be mobile and exchange information in a peer-to-peer fashion. We consider both cases of nodes with largeand small-sized caches. For large-sized caches, we devise a strategy where nodes, independent of each other, decide whether to cache some content and for how long. In the case of small-sized caches, we aim to design a content replacement strategy that allows nodes to successfully store newly received information while maintaining the good performance of the content distribution system. Under both conditions, each node takes decisions according to its perception of what nearby users may store in their caches and with the aim of differentiating its own cache content from the other nodes’. The result is the creation of content diversity within the nodes neighborhood so that a requesting user likely finds the desired information nearby. We simulate our caching algorithms in different ad hoc network scenarios and compare them with other caching schemes, showing that our solution succeeds in creating the desired content diversity, thus leading to a resource-efficient information access. INTRODUCTION PROVIDING information to users on the move is one of the most promising directions of the infotainment business, which rapidly becomes a market reality, because infotainment modules are deployed on cars and handheld devices. The ubiquity and ease of access of third- and fourth-generation (3G or 4G) networks will encourage users to constantly look for content that matches their interests. However, by exclusively relying on downloading from the infrastructure, novel applications such as mobile multimedia are likely to overload the wireless network (as recently happened to AT&T following the introduction of the iPhone [1]). It is thus conceivable that a peer-to-peer system could come in handy, if used in conjunction with cellular networks, to promote content sharing using ad hoc networking among mobile users [2]. RELATED WORK Several papers have addressed content caching and content replacement in wireless networks. In the following sections, we review the works that aremost related to this paper, highlighting the differences with respect to the Hamlet framework that we propose. Cooperative Caching In [9], distributed caching strategies for ad hoc networks are presented according to which nodes may cache highly popular content that passes by or record the data path and use it to redirect future requests. Among the schemes presented in [9], the approach called HybridCache best matches the operation and system assumptions that we consider; we thus employ it as a benchmark for Hamlet in our comparative evaluation. In [10], a cooperative caching technique is presented and shown to provide better performance than HybridCache. However, the solution that was proposed is based on the formation of an overlay network composed of “mediator” nodes, and it is only fitted to static connected networks with stable links among nodes. These assumptions, along with the significant communication overhead needed to elect “mediator” nodes, make this scheme unsuitable for the mobile environments that we address. The work in [11] proposes a complete framework for information retrieval and caching in mobile ad hoc networks, and it is built on an underlying routing protocol and requires the manual setting of a networkwide “cooperation zone” parameter. Note that assuming the presence of a routing protocol can prevent the adoption of the scheme in [11] in highly mobile networks, where maintaining network connectivity is either impossible or more communication expensive than the querying/caching process. Furthermore, the need of a manual calibration of the “cooperation zone” makes the scheme hard to configure, because different environments are considered. Conversely, Hamlet is self contained and is designed to self adapt to network environments with different mobility and connectivity features. Data Replication Although addressing a different problem, some approaches to data replication are relevant to the data caching solution that we propose. One technique of eliminating information replicas among neighboring nodes is introduced in [21], which, unlike Hamlet, requires knowledge of the information access frequency and periodic transmission of control messages to coordinate the nodes’ caching decisions. In [5], the authors propose a replication scheme that aims at having every node close to a copy of the information and analyze its convergence time. However, unlike Hamlet, the scheme implies a significant overhead and an exceedingly high convergence time, thus making it unsuitable for highly variable networks. Finally, the work in [22] adopts a cross-layer approach to data replication in mobile ad hoc networks, where network-layer information on the node movement path helps to trigger the replication before network partitioning occurs. SYSTEM OUTLINE AND ASSUMPTIONS Hamlet is a fully distributed caching strategy for wireless ad hoc networks whose nodes exchange information items in a peer-to-peer fashion. In particular, we address a mobile ad hoc network whose nodes may be resource-constrained devices, pedestrian users, or vehicles on city roads. Each node runs an application to request and, possibly, cache desired information items. Nodes in the network retrieve information items from other users that temporarily cache (part of) the requested items or from one or more gateway nodes, which can store content or quickly fetch it from the Internet. We assume a content distribution system where the following assumptions hold: 1) A number I of information items is available to the users, with each item divided into a number C of chunks; 2) user nodes can overhear queries for content and relative responses within their radio proximity by exploiting the broadcast nature of the wireless medium; and 3) user nodes can estimate their distance in hops from the query source and the responding node due to a hop-count field in the messages. Although Hamlet can work with any system that satisfies the aforementioned three generic assumptions, for concreteness, we detail the features of the specific content retrieval system that we will consider in the remainder of this paper. HAMLET FRAMEWORK The Hamlet framework allows wireless users to take caching decisions on content that they have retrieved from the network. The process that we devise allows users to take such decisions by leveraging a node’s local observation, i.e., the node’s ability to overhear queries and information messages on the wireless channel. In particular, for each information item, a node records the distance (in hops) of the node that issues the query, i.e., where a copy of the content is likely to be stored, and the distance of the node that provides the information. Based on such observations, the node computes an index of the information presence in its proximity for each of the I items. Small-Sized Caches: Content Replacement When equipped with a small-sized cache, nodes cannot store all content that they request but are forced to choose which items to keep and which items to discard every time newly retrieved data fill up their memory. In this case, computing cache drop times is clearly not a solution, because the lingering of items in cache is primarily determined by the rate of reception of new content. Therefore, in the presence of limited dedicated storage resources, we exploit the information presence estimate to define a content replacement policy that favors a balanced distribution of data over the network so that all content is as “close” as possible to a requesting node. SIMULATION SCENARIOS AND METRICS We tested the performance of Hamlet through ns2 simulations under the following three different wireless scenarios: 1) a network of vehicles that travel in a city section (referred to as City); 2) a network of portable devices carried by customers who walk in a mall (Mall); and 3) a network of densely and randomly deployed nodes with memory limitations (memoryconstrained nodes). The three scenarios are characterized by different levels of node mobility and network connectivity. In the City scenario, as depicted in Fig. 4, vehicle movement is modeled by the intelligent driver model with intersection management (IDM-IM), which takes into account car-to-car interactions and stop signs or traffic lights [27]. We simulated a rather sparse traffic, with an average vehicle density of 15 veh/km over a neighborhood of 6.25 km2. The mobility model settings, forcing vehicles to stop and queue at intersections, led to an average vehicle speed of about 7 m/s (i.e., 25 km/h). We set the radio range to 100 m in the vehicular scenario, and by analyzing the network topology during the simulations, we observed an average link duration of 24.7 s and a mean of 45 disconnected node clusters concurrently present over the road topology. The City scenario is thus characterized by scattered connectivity and high node mobility. EVALUATION WITH SMALL-SIZED CACHES We now evaluate the performance of Hamlet in a network where a node cache can accommodate only a small portion of the data that can be retrieved in the network. As an example, consider a network of low-cost robots that are equipped with sensor devices, where maps that represent the spatial and temporal behavior of different phenomena may be needed by the nodes and have to be cached in the network. We thus consider the memory-constrained scenario introduced in Section V and employ the Hamlet framework to define a cache replacement strategy, as detailed in Section IV. In such a scenario, the caching dynamics of the different information items become strongly intertwined. Indeed, caching an item often implies discarding different previously stored content, and as a consequence, the availability of one item in the proximity of a node may imply the absence of another item in the same area. Thus, in our evaluation, it is important to consider a large number of items, as well as to differentiate among these items in terms of popularity. We consider an overall pernode query rate Λ = 0.1 and sets of several hundreds of items. We assume that popularity levels qi are distributed according to the Zipf law, which has been shown to fit popularity curves of content in different kinds of networks [29]. CONCLUSION We have introduced Hamlet, which is a caching strategy for ad hoc networks whose nodes exchange information items in a peer-to-peer fashion. Hamlet is a fully distributed scheme where each node, upon receiving a requested information, determines the cache drop time of the information or which content to replace to make room for the newly arrived information. These decisions are made depending on the perceived “presence” of the content in the node’s proximity, whose estimation does not cause any additional overhead to the information sharing system. We showed that, due to Hamlet’s caching of information that is not held by nearby nodes, the solving probability of information queries is increased, the overhead traffic is reduced with respect to benchmark caching strategies, and this result is consistent in vehicular, pedestrian, and memoryconstrained scenarios. |
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