Alicia Triviño-Cabrera

An analytical model to estimate path duration in MANETs

Mobile Ad Hoc Networks (MANETs) are strongly impacted by the mobility of the ad hoc nodes. Mobility models help engineers to abstract the changes of position in network users. Different mobility models have already been proposed to characterize the behaviors of mobile devices that are greatly correlated to the conditions of the possible scenarios where networks can be deployed. In the context of mobile ad hoc networks, the Random WayPoint model has received significant attention and it has become one of the most employed mobility patterns. However, a formal description of the time during which a generic N-hop path is valid has not been proposed yet for this model. In this paper, the authors provide an analytical model for link duration as well as an analytical study of path duration in multi-hop wireless networks. The predicted results are compared with measured data and good agreement is reported.

Ad hoc routing based on the stability of routes

Some reactive ad hoc protocols allow the discovery and/or storage of multiple paths to the same destination node. The selection of the path to utilize is commonly based on the criterion of the minimum number of hops. However, some other strategies could be appropriate to improve the network performance. In this paper, we intend to minimize the load in the network by choosing the most stable path, i.e. the path which is expected to have the longest lifetime. With this purpose, we estimate the stability of the path by means of the received signal strength. The simulations show that important improvements associated to the network performance are achieved by the use of this cross-layer information.

Application of path duration study in multihop ad hoc networks

Some ad hoc protocols allow the discovery and/or storage of multiple routes to the same destination node. The selection of the path to utilize is commonly based on the criterion of the minimum number of hops. However, other strategies could be more appropriate to improve the network performance. In this sense, this paper proposes the criterion based on the estimation of the Mean Residual Path Lifetime. In order to compute this metric, a formal description of link duration in mobile ad hoc networks is presented. The model has been verified by means of simulations enclosing different mobility and transmission conditions. From the link duration model, an analytical expression for path duration and mean residual lifetime is then derived. Finally, the authors show that selected ad hoc routing paths live longer when the proposed criterion is employed.

A cross layer interception and redirection cooperative caching scheme for MANETs

The caching paradigm has widely been used in computers, data bases and the Internet to reduce the response time of the applications and to reduce the traffic load in the computer buses or in the networks. These advantages can also be applied in a Mobile Ad Hoc Network (MANET) as the caching paradigm could reduce the interferences due to the traffic overload and it could also increase the availability of the documents due to server disconnections. In this article, we propose a cooperative caching scheme for MANETs. The proposal is supported by the local cache that all the nodes in the MANET possess. In a collaborative way, a node could respond to the demand of other nodes if it is keeping a valid copy of the required document. As a novelty, the demands of the documents are not restricted to specific application messages but they are codified into the messages generated when the path to the server is being searched. In this way, the documents can be retrieved even when there is no route to the server. Furthermore, these expanded messages provide useful information about potential localizations of the documents. The proposed technique will use those additional location data to redirect the requests. By means of simulations, we have evaluated and compared our proposal to five other caching schemes as well as with the option of no caching. The obtained results indicate that our proposal outperforms the others in terms of document accessibility, delay and generated traffic load.

Characterizing Document Types to Evaluate Web Cache Replacement Policies

In this paper, a study of the performance of six replacement policies has been developed. Three of them are classical caching algorithms (LRU, LFU and LFU-DA) while the other three are caching schemes specifically developed for Web documents (GO-SIZE, GDSF and GD*). This study has been divided by the main content-types observed in Web traffic (application, audio, images, text and video). Using a trace log of a real proxy cache, a characterization of the main properties of the documents has been performed, such as size characteristics, popularity and temporal locality. Finally, a trace driven simulation study of the performance of the replacement policies has been developed for the traffic generated by each considered content-type

Proposal and evaluation of an application level caching scheme for ad hoc networks

In this paper, we describe a caching scheme for ad hoc networks. In this proposal the wireless nodes implement a local cache so that consecutive requests to the same document can be served directly by their own local cache instead of accessing the remote server. The nodes can also intercept the forwarding requests and serve the documents requested directly using their local cache. On the other hand the nodes learn where the documents are located using the information of the request and response messages that they forward. Using this information the nodes can redirect the requests to other nodes that are known to have the document requested and that are closer than the original destination of the request. By means of simulations we demonstrate that these proposals reduce the latency perceived by the nodes.

Proposal and Evaluation of a Caching Scheme for Ad Hoc Networks

In this paper, we describe and evaluate the performance of a caching scheme for ad hoc networks. In this proposal the wireless nodes store the documents they request in a local cache and they can also work as a server for the other wireless nodes if they intercept the forwarding requests and serve the documents requested directly using their local cache. On the other hand, the wireless nodes inspect the requests and responses that they forward in order to learn where and how far the documents are located and they use this information to redirect the requests to other nodes that are closer than the original destination of the request. By means of simulations we evaluate the performance of the proposal and demonstrate that they reduce the latency perceived by the nodes.

A windows based web cache simulator tool

In this paper, we describe a Windows based Web cache simulator tool. This tool is able to process the IRCache based traces files and reproduce the behavior of a Web Proxy Cache. It can be configured to simulate fifteen replacement policies and two admission control policies. The cache size, the percentage of warm-up and the cost function of some replacement policies can also be configured. The simulations can be performed in a batch process and the results are stored in text format files that can be automatically analyzed using other tools like Matlab to obtain performance graphs.

Two new metrics to evaluate the performance of a Web cache with admission control

This work presents a new metric that calculates the performance of a Web cache with admission control. This metric is an alternative to the classic hit rate (HR) and byte hit rate (BHR) that has been especially developed to measure the effectiveness of the cache when there is an admission control policy that decides if a new document that reaches the cache must be cached. Additionally, a second metric that computes the capacity of the admission control to reject documents that are referenced only one time or are modified from reference to reference, has been proposed. We have evaluated the ability of the metrics by means of simulation of a cache that considers the least recently used (LRU) replacement policy and an admission control that rejects the documents based on their size

Identification of Stable Links in MANETs

Mobile Ad Hoc Networks (MANET) are characterized by a highly dynamic topology as a consequence of the frequent and unpredictable changes in the link states. Routing protocols must cope with this eventuality so when routes in use break, they should discover alternative paths to keep the on-going communications active. The procedures to discover new routes commonly provoke a significant amount of control packets which may induce losses and delay to the data packets. Therefore, the network performance could benefit from the techniques that avoid these route discovery procedures. In this sense, a practical strategy is the use of the links that are expected to endure longer. Basing on an analytical model, this paper presents a technique to identify the most stable links. The evaluation in an autonomous MANET connected to the Internet shows the goodness of the proposed criterion.