Summary The WAND processing strategy is a dynamic pruning algorithm designed for large scale Web search engines where fast response to queries is a critical service. The WAND is used to reduce the amount of computation by scoring only documents that may become part of the top‐k document results. In this paper, we present two parallel strategies for the WAND algorithm and compare their performance on GPUs. In our first strategy (named size‐based), the posting lists are evenly partitioned among thread blocks. Our second strategy (named range‐based) partitions the posting lists according to document identifier intervals; thus, partitions may have different sizes. We also propose three threshold sharing policies, named Local, Safe‐R, and Safe‐WR, which emulate the WAND algorithm global pruning technique. We evaluated our proposals with different amounts of work, from short to extra‐large queries, using single query processing and batch of queries. Results show that the size‐based strategy reports the highest speedups but at the cost of low quality of results. The range‐based algorithm retrievals the exact top‐k documents and maintains a good speedup. Moreover, both strategies are capable of scaling as the amount of work is increased. In addition, there is no significant difference in the performance of the three threshold sharing policies.

MaxScore and its variations are efficient DAAT query evaluation methods which use dynamic pruning based on the potential relevance of documents, to provide fast and precise results. These are essential characteristics for large scale search engines. In an attempt to circumvent the inherent sequential nature of DAAT strategies, we applied two parallel strategies to implement new variations of MaxScore to execute on GPUs. The first strategy splits the posting lists based on their size to share the work among thread blocks and SMs of a GPU, while the second strategy partitions the posting lists based on the range of document IDs (docIDs). In order to improve the pruning efficiency of the parallel algorithms, we also evaluated three different strategies for sharing the threshold among the processing elements. Experiments were carried out under different sizes of the postings list, and results demonstrate the viability of both strategies and their GPU-based implementations. The sizebased partitioning showed higher speedups (18×) but lower recall for retrieved documents, while the docID-based partitioning can retrieve the exact top-k documents with slightly lower speedups (16×). Threshold sharing demonstrated significant performance gains for long postings lists. As novelty and contribution, to the best of our knowledge, this is the first parallelization of MaxScore for GPUs. Results show that our strategies are suitable for the parallelization of a class of DAAT strategies on GPUs.

In this paper we propose and evaluate new strategies for the parallel top-k query processing on GPUs. Our strategies are based on the document-at-a-time approach and have been implemented and tested with the WAND ranking algorithm. In our first strategy (named homogeneous), the posting lists are evenly partitioned among thread blocks. Our second algorithm, named heterogeneous, partitions the posting lists according to document identifier intervals, thus partitions may have different sizes. We also propose three threshold sharing policies, named Local, Safe-R and Safe-WR, which emulate the WAND algorithm global pruning technique. We evaluated our proposals using AND/OR queries, and the results show that the homogeneous algorithm allows better speedups through higher occupancy of the SMs, but at the cost of a lower recall. The heterogeneous algorithm produces the exact top-k documents and shows promising speedups. Also, the Shared-R and Shared-WR policies for threshold propagation allowed better performance, provided there is enough amount of work per thread block, which proved true for queries composed of at least a few millions documents.

Several existing IP mobility solutions use invasive approaches, when adjustments in legacy protocols from the TCP/IP stack are necessary, or rely on specific network infrastructures. We devised an architecture to handle mobility using a Session-based Mobile Socket Layer (SMSL). With no need for software adaptation in the core of the network or adjustment on the TCP/IP stack, SMSL operates only at the end systems involved in the communication, being fully transparent to neighboring Transport and Application layers. The session scheme allows mobility awareness for TCP-based applications that require resilience to failures, delays, or disconnection. A general-purpose API extended from the Socket and implemented in GNU/Linux provides session services, such as tracking mobile peers, detecting disruptions, and suspending and resuming sessions with efficiency, security, and reliability. In this paper, we present the entire session support system as a mature work of research achieved with advances made in our previous study. The results of experiments in real and emulated test environments demonstrate efficiency. SMSL introduces little overhead, with a mean goodput degradation of 6.9% compared to an application implemented on top of the standard TCP/IP stack. Disruptions are detected in microseconds and suspended sessions resume in milliseconds for single-homed mobile nodes.

Current ubiquitous computing technologies provide access to customized, contextual, and location-based services. Device mobility, however, is frequently associated with communication delays, link disruptions due to signal loss, and changes in IP address. As a result, connection-oriented applications may fail and node location strategies should not rely on node addresses. In this paper, we propose the use of communication sessions to create mobility-aware applications that do not break with transmission delays or disruptions. The concept of these communication sessions is embedded in the basic network socket API functions and operates transparently with the applications. Sessions provide application level support to keep track of the location of peer nodes, to detect connection disruptions, and to suspend and resume transmissions. Experiments show our approach offers superior performance of the general IP layer mobility solution, with no need to implement or adapt software at the core network infrastructure.

A huge effort has been applied on the study of wireless mesh networks (WMNs) over the last few years. As part of this effort the IEEE 802.16 standard for local and metropolitan area networks specifies a mesh mode of operation. Although several technical aspects of the physical and medium access layers of the standard have been studied, only few works investigate how the WiMAX mesh mode architecture will handle billing aspects and paid access. Here we propose a billing architecture and present an accounting mechanism which allows WISPs to charge its users and also reward those who contribute forwarding packets. We evaluate the accounting mechanism through simulations and show its feasibility.

We introduce the ProGrid system, an architecture for computational grids, whose communication and resource management infrastructure is used transparently by the applications. Unlike other grid approaches, either application-centric or system-centric, the model relies on the use of proxy servers to perform additional communications and authentication procedures on behalf of client applications. The purpose of this mechanism is to enable parallel applications to be executed in geographically distributed environments interlinked by an open communication network, such as the Internet, meeting the security requisites desirable for computational grids. Among the common services of a grid, we focus on safe communication and the controlled sharing of available resources. To identify the resources, standards under development are considered for the specification of objects in grids. We also discuss an extension of the functionality of proxy servers to include support for the standardized management of the grid and of the available objects.