Reduce Download Time Research Articles

The Role of Hysteresis in Caching Systems

Caching is a fundamental element of networking systems since the early days of the Internet. By filtering requests toward custodians, caches reduce the bandwidth required by the latter and the delay experienced by clients. The requests that are not served by a cache, in turn, comprise its miss stream. We refer to the dependence of the cache state and miss stream on its history as hysteresis. Although hysteresis is at the core of caching systems, a dimension that has not been systematically studied in previous works relates to its impact on caching systems between misses, evictions, and insertions. In this article, we propose novel mechanisms and models to leverage hysteresis on cache evictions and insertions. The proposed solutions extend TTL-like mechanisms and rely on two knobs to tune the time between insertions and evictions given a target hit rate. We show the general benefits of hysteresis and the particular improvement of the two thresholds strategy in reducing download times, making the system more predictable and accounting for different costs associated with object retrieval.

Download Time Analysis for Distributed Storage Codes With Locality and Availability

The paper presents techniques for analyzing the expected download time in distributed storage systems that employ systematic availability codes. These codes provide access to hot data through the systematic server containing the object and multiple recovery groups. When a request for an object is received, it can be replicated (forked) to the systematic server and all recovery groups. We first consider the low-traffic regime and present the close-form expression for the download time. By comparison across systems with availability, maximum distance separable (MDS), and replication codes, we demonstrate that availability codes can reduce download time in some settings but are not always optimal. In the high-traffic regime, the system contains multiple inter-dependent Fork-Join queues, making exact analysis intractable. Accordingly, we present upper and lower bounds on the download time, and an M/G/1 queue approximation for several cases of interest. Via extensive numerical simulations, we evaluate our bounds and demonstrate that the M/G/1 queue approximation has a high degree of accuracy.

DPRS: A dynamic popularity aware replication strategy with parallel download scheme in cloud environments

Cloud computing has emerged as a main approach for managing huge distributed data in different areas such as scientific operations and engineering experiments. In this regard, data replication in Cloud environments is a key strategy that reduces response time and improves reliability. One of the main features of a distributed environment is to replicate data in various sites such that popular data would be more available. Whenever a site does not have a needed data file, it will have to fetch it from other locations. Therefore, the parallel download approach is applied to reduce download time. It enables a user to get various parts of a file from several sites simultaneously. In this work, we present a data replication strategy, named the Dynamic Popularity aware Replication Strategy (DPRS), which is presented on Cloud system leveraging data access behavior. DPRS replicates only a small amount of frequently requested data file based on 80/20 idea. It determines to which site the file is replicated based on number of requests, free storage space, and site centrality. We introduce a parallel downloading approach that replicates data segments and parallel downloads replicated data fragments, to enhance the overall performance. We evaluate effective network usage, mean job execution time, hit ratio, total number of replications and percentage of storage filled by using the CloudSim simulator. Extensive experimentations demonstrate the effectiveness of DPRS under most of access patterns.

Pushing CDN-ISP collaboration to the limit

Today a spectrum of solutions are available for istributing content over the Internet, ranging from commercial CDNs to ISP-operated CDNs to content-provider-operated CDNs to peer-to-peer CDNs. Some deploy servers in just a few large data centers while others deploy in thousands of locations or even on millions of desktops. Recently, major CDNs have formed strategic alliances with large ISPs to provide content delivery network solutions. Such alliances show the natural evolution of content delivery today driven by the need to address scalability issues and to take advantage of new technology and business opportunities. In this paper we revisit the design and operating space of CDN-ISP collaboration in light of recent ISP and CDN alliances. We identify two key enablers for supporting collaboration and improving content delivery performance: informed end-user to server assignment and in-network server allocation. We report on the design and evaluation of a prototype system, NetPaaS, that materializes them. Relying on traces from the largest commercial CDN and a large tier-1 ISP, we show that NetPaaS is able to increase CDN capacity on-demand, enable coordination, reduce download time, and achieve multiple traffic engineering goals leading to a win-win situation for both ISP and CDN.

PROBING HIGH-CAPACITY PEERS TO REDUCE DOWNLOAD TIMES IN P2P FILE SHARING SYSTEMS WITH STOCHASTIC SERVICE CAPACITIES

The main problem for an individual user peer in a peer-to-peer network with heterogeneous source peers is the peer selection problem, namely, switching among source peers and finally settling on one, while keeping the total time of probing and downloading to a minimum. There has been little investigation on selecting source peers with stochastic service capacities. The main contribution of this paper is to address the problem of reducing download times in peer-to-peer file sharing systems with stochastic service capacities. A precise analysis of the expected download time is given when the service capacity of a source peer is a random variable. A chunk-based switching and peer selection algorithm using the method of probing high-capacity peers is proposed and the expected download time of the algorithm is analyzed. Two subproblems of the optimal choice of the threshold of high-capacity source peers and the optimal order of probing are also solved. The performance of the algorithm is compared with the random chunk-based switching method. It is shown that noticeable performance improvement can be obtained.

Coarse-grain replica management strategies for dynamic replication of Web contents

This paper discusses replica management strategies for cost-effective, scalable Web content distribution. In terms of the granularity of replica contents, current dynamic replication approaches can be classified into entire replication (entire content is replicated) and object replication (individual objects are replicated) schemes. However, while the former cannot effectively reduce client download time and server load due to the coarsest replication granularity, the latter requires a large overhead to manage replica locations due to per-object request redirection. We propose schemes to deliver almost as effective performance to reduce download time and server load as in the object replication scheme while they require almost as small overhead to manage replica locations as the entire replication scheme. The schemes aggregate objects in the origin server into multiple content groups and then replicate them on per-group granularity. Per-group request redirection can significantly reduce an overhead to manage replica locations. The content groups are either statically created in advance or dynamically created upon replication. The approach of dynamic grouping uses a URL rewriting technique to enable per-group request redirection. We evaluate the performance to reduce download time and server load in the proposed schemes changing the number of created content groups. The scheme of dynamic group creation achieves almost the same performance characteristic to reduce download time as the object replication scheme with a significantly smaller overhead to manage replica locations. Even the scheme of static group creation provides much better performance than entire replication under a skewed request distribution. The proposed scheme, which addresses URL inconsistency problems derived from the URL rewriting, preserves high download time reduction performance with insignificant overhead of replica management.

Mitigating server-side congestion in the Internet through pseudoserving

Server-side congestion arises when a large number of users wish to retrieve files from a server over a short period of time. Under such conditions, users are in a unique position to benefit enormously by sharing retrieved files. Pseudoserving, a new paradigm for Internet access, provides incentives for users to contribute to the speedy dissemination of server files through a contract set by a "superserver". Under this contract, the superserver grants a user a referral to where a copy of the requested file may be retrieved in exchange for the user's assurance to serve other users for a specified period of time. Simulations that consider only network congestion occurring near the server show that: (1) pseudoserving is effective because it self-scales to handle very high request rates; (2) pseudoserving is feasible because a user who participates as a pseudoserver benefits enormously in return for a relatively small contribution of the user's resources; (3) pseudoserving is robust under realistic user behavior because it can tolerate a large percentage of contract breaches; and (4) pseudoserving can exploit locality to reduce usage of network resources. Experiments performed on a local area network that account for the processing of additional layers of protocols and the finite processing and storage capacities of the server and the clients, corroborate the simulation results. They also demonstrate the benefits of exploiting network locality in reducing download times and network traffic while making referrals to a pseudoserver. Limitations of pseudoserving and potential solutions to them are also discussed.