To relieve the heavy data transmission pressure caused by duplicate requests from user equipments (UEs) on base stations (BSs), edge caching is envisioned as an effective method to help BSs for ...traffic offloading. In D2D networks, pre-cache the various files for mobile users is a crucial issue to improve the network performance. Therefore, an effective cache placement scheme is necessary to reduce cache redundancy and capacity waste. In this paper, the cache placement problem is investigated for cache redundancy reduction. Considering that users’ mobility has a non-negligible impact on the system performance, we model the users’ mobility as a continuous-time Markov chain (CTMC) in which the user’s encounter probability is estimated using the historical contact time and inter-contact time among users. Then, the contact intensity and the interest similarity are modeled to represent social relationship intensity among users. Integrating the users’ mobility with the social relationship, a social relationship graph is constructed. Subsequently, we formulate the file placement problem as a many-to-many matching problem and we propose a novel file placement algorithm to make decisions on cache placement based on the social relationship graph with low computational complexity and low caching redundancy. Simulation results show that the proposed algorithm can achieve better performance compared with the existing caching placement schemes under the limited storage capacity.
Unmanned-aerial-vehicle (UAV) enabled radio access is an effective technology to improve the wireless coverage, in particular for remote and disaster-struck areas. It will become a key enabler in the ...forthcoming 5G heterogeneous cellular networks to provide improved and resilient coverage. In this article, we study edge caching for multiple UAV-enabled radio access networks (UAV-RANs) and investigate how the overall spectral efficiency (SE) can be improved by efficient edge caching. In this context, UAV base stations (UBSs) may not serve the immediate close-by users, but serve the users based on the requested contents, which brings the service contents closer to users. Based on analyses of the SE achieved by the content-centric UAV-RAN, a hybrid caching strategy is proposed to further improve the SE. In order to cache more files with limited cache resources while guaranteeing the quality-of-service, the contents are divided into two subsets, a popular set and a less popular set, based on their popularity profile that follows Zipf distribution. The popular files, according to the proposed hybrid caching strategy, are cached at all the UBSs, while each less popular file is cached at one UBS only. The overall SE is maximized by finding an optimal popularity threshold between the two subsets. By relaxing the formulated problem, analytical expression for the optimized threshold is derived. The effectiveness of the proposed method is verified by numerical examples where existing benchmark schemes are compared and outperformed.
This paper presents a classification of file placement and replication methods on grids. The study is motivated by file transfer issues encountered in the Virtual Imaging Platform deployed on the ...European Grid Infrastructure. Approaches proposed in the last 6 years are classified using taxonomies of replication process, replication optimization, file models, resource models and replication validation. Most existing approaches implement file replication as a middleware service, using dynamic strategies. Production approaches are slightly different than works evaluated in simulation or in controlled conditions which (i) mostly assumes simplistic file models (undistinguished read-only files), (ii) rely on elaborated access patterns, (iii) assume clairvoyance of the infrastructure parameters and (iv) study file availability less than other metrics but insist on cost.
► We propose a classification of file replication and placement methods on grids. ► We review works published during the past 6 years. ► We highlight singularities of approaches deployed in production.
Prompt response to data access requests is the key performance concern of parallel storage systems. Sort partition (SP) is one of the most promising file allocation solutions for the static scenario ...due to its sorted partition and placing mechanism. The online variant of SP, hybrid partition (HP), however, does not perform well in the dynamic scenario. The recently proposed balanced allocation with sort (BAS) and its online version balanced allocation with sort for batch (BASB) try to compete with SP and HP by providing better load balancing together with sorting. BAS's performance is close to SP, and BASB greatly outperforms HP. In this paper, we proposed new file placement solutions for the parallel storage systems: Optimized Sort Partition (OSP) for the static scenario and Optimized Sort Partition Online (OSPOnline) for the dynamic scenario. By eliminating the drawbacks of SP/HP and BAS/BASB in the file assignment, OSP and OSPOnline can achieve optimized system response time. Conducted simulations show that OSP and OSPOnline steadily outperform their competitors under various conditions.
We investigate the placement of
N enterprise data-stores (e.g., database tables, application data) across an array of disks with the aim of minimizing the response time averaged over all served ...requests, while balancing the load evenly across all the disks in the parallel disk array. Incorporating the non-FCFS serving discipline and non-work-conserving nature of disk drives in formulation of the placement problem is difficult and current placement strategies do not take them into account.
We present a novel formulation of the placement problem to incorporate these crucial features and identify the runlength of requests accessing a store as the most important criterion for placing the stores. We use these insights to design a fast (running time of
N
log
N
) placement algorithm that is optimal under the assumption that transfer times are small. Further, we develop polynomial-time extensions of the algorithm that minimize response time even if transfer times are large, while balancing the loads across the disks. Comprehensive experimental studies establish the efficacy of the proposed algorithm under a wide variety of workloads with the proposed algorithm reducing the response time for real storage traces by more than a factor of 2 under heterogeneous workload scenarios.
Multicluster interleaving on paths and cycles Jiang, A.; Bruck, J.
IEEE transactions on information theory,
2005-Feb., 2005-02-00, 20050201, Letnik:
51, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Interleaving codewords is an important method not only for combatting burst errors, but also for distributed data retrieval. This paper introduces the concept of multicluster interleaving (MCI), a ...generalization of traditional interleaving problems. MCI problems for paths and cycles are studied. The following problem is solved: how to interleave integers on a path or cycle such that any m (m/spl ges/2) nonoverlapping clusters of order 2 in the path or cycle have at least three distinct integers. We then present a scheme using a "hierarchical-chain structure" to solve the following more general problem for paths: how to interleave integers on a path such that any m (m/spl ges/2) nonoverlapping clusters of order L (L/spl ges/2) in the path have at least L+1 distinct integers. It is shown that the scheme solves the second interleaving problem for paths that are asymptotically as long as the longest path on which an MCI exists, and clearly, for shorter paths as well.
Advances in computing and networking are generating a significant demand for video-on-demand (VOD) applications. In this paper, the condition for minimum blocking probability of a VOD system is ...derived. The optimal load-sharing requirement in such a system is found so that the minimum blocking probability is achieved. A combination of genetic algorithm and modified bin-packing algorithm is then developed for the multimedia file placement exercise. It is demonstrated that a specified blocking probability can be achieved while the capacity usage is minimized simultaneously.
To chunk or not to chunk Summers, Jim; Brecht, Tim; Eager, Derek ...
Proceedings of the 22nd international workshop on Network and Operating System Support for Digital Audio and Video,
06/2012
Conference Proceeding
Large amounts of Internet streaming video traffic are being delivered using HTTP to leverage the existing web infrastructure. A fundamental issue in HTTP streaming concerns the granularity of video ...objects used throughout the HTTP ecosystem (including clients, proxy caches, CDN nodes, and servers). A video may be divided into many files (called chunks), each containing only a few seconds of video at one extreme, or stored in a single unchunked file at the other.
In this paper, we describe the pros and cons of using chunked and unchunked videos. We then describe a methodology for fairly comparing the performance implications of video object granularity at web servers. We find that with conventional servers (userver, nginx and Apache) there is little performance difference between these two approaches. However, by aggressively prefetching and sequentializing disk accesses in the userver, we are able to obtain up to double the throughput when serving requests for unchunked videos when compared with chunked videos (even while performing the same aggressive prefetching with chunked videos). These results indicate that more research is required to ensure that the HTTP ecosystem can handle this important and rapidly growing workload.
Prompt response to data access requests is the key performance concern of parallel storage systems. To the best of our knowledge, Sort Partition (SP) is one of the most promising file allocation ...solutions in the static scenario due to its sorted partition and placing mechanism. The online variant of SP, Hybrid Partition (HP), however, does not perform well in the dynamic scenario. The recently proposed Balanced Allocation with Sort (BAS) and its online version Balanced Allocation with Sort for Batch (BASB) try to compete with SP and HP by providing better load balancing together with sorting. BAS's performance is close to SP, and BASB performs much better than HP in the dynamic scenario. In this paper, we proposed new file placement solutions for the parallel storage systems: Optimized Sort Partition (OSP) for the static scenario and Optimized Sort Partition Online (OSPOnline) for the dynamic scenario. By eliminating the drawbacks of SP/HP and BAS/BASB in the file assignment, OSP and OSPOnline can always achieve optimized sort partition and good load balancing simultaneously. Conducted simulations show that OSP and OSPOnline steadily outperform their competitors under various conditions.
While hard disk drives are the most common secondary storage devices, their high power consumption and low shock-resistance limit them as an ideal mobile storage solution. On the other hand, flash ...memory devices overcome the main problems of hard disk drives, but they are still more expensive in the cost per bit over hard disk drives and can only support a limited number of erase cycles. In this paper, we show that combining the merits of a hard disk and a flash memory device can produce an energy-efficient secondary storage solution for mobile platforms. We propose an energy-efficient file placement technique for such heterogeneous storage systems. The proposed technique adapts an existing data concentration technique by separating read and write I/O requests. Experimental results show that the proposed technique reduces the energy consumption by up to 74.5% when the combination of a 1.8" disk and a flash memory is used instead of a single 2.5" disk, at the cost of small increase in the average response time.
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