153 research outputs found
Audience-retention-rate-aware caching and coded video delivery with asynchronous demands
Most of the current literature on coded caching focus on a static scenario, in which a fixed number of users synchronously place their requests from a content library, and the performance is measured in terms of the latency in satisfying all of these requests. In practice, however, users start watching an online video content asynchronously over time, and often abort watching a video before it is completed. The latter behaviour is captured by the notion of audience retention rate, which measures the portion of a video content watched on average. In order to bring coded caching one step closer to practice, asynchronous user demands are considered in this paper, by allowing user demands to arrive randomly over time, and both the popularity of video files, and the audience retention rates are taken into account. A decentralized partial coded delivery (PCD) scheme is proposed, and two cache allocation schemes are employed; namely homogeneous cache allocation (HoCA) and heterogeneous cache allocation (HeCA), which allocate users’ caches among different chunks of the video files in the library. Numerical results validate that the proposed PCD scheme, either with HoCA or HeCA, outperforms conventional uncoded caching as well as the state-of-the-art decentralized caching schemes, which consider only the file popularities, and are designed for synchronous demand arrivals. An information-theoretical lower bound on the average delivery rate is also presented
Coded caching: Information theoretic bounds and asynchronism
Caching is often used in content delivery networks as a mechanism for reducing network traffic. Recently, the technique of coded caching was introduced whereby coding in the caches and coded transmission signals from the central server were considered. Prior results in this area demonstrate that carefully designing the placement of content in the caches and designing appropriate coded delivery signals from the server allow for a system where the delivery rates can be significantly smaller than conventional schemes.
However, matching upper and lower bounds on the transmission rate have not yet been obtained. In the first part of this thesis we derive tighter lower bounds on the coded caching rate than were known previously. We demonstrate that this problem can equivalently be posed as a combinatorial problem of optimally labeling the leaves of a directed tree. Our proposed labeling algorithm allows for significantly improved lower bounds on the coded caching rate. Furthermore, we study certain structural properties of our algorithm that allow us to analytically quantify improvements on the rate lower bound for general values of the problem parameters. This allows us to obtain a multiplicative gap of at most four between the achievable rate and our lower bound.
The original formulation of the coded caching problem assumes that the file requests from the users are synchronized, i.e., they arrive at the server at the same time. Several subsequent contributions work under the same assumption. Furthermore, the majority of prior work does not consider a scenario where users have deadlines. In the second part of this thesis we formulate the asynchronous coded caching problem where user requests arrive at different times. Furthermore, the users have specified deadlines. We propose a linear program for obtaining its optimal solution. However, the size of the LP (number of constraints and variables) grows rather quickly with the number of users and cache sizes. To deal with this problem, we explore a dual decomposition based approach for solving the LP under consideration. We demonstrate that the dual function can be evaluated by equivalently solving a number of minimum cost network flow algorithms.
Moreover, we consider the asynchronous setting where the file requests are revealed to the server in an online fashion. We propose a novel online algorithm for this problem building on our prior work for the offline setting (where the server knows the request arrival times and deadlines in advance). Our simulation results demonstrate that our proposed online algorithm allows for a natural tradeoff between the feasibility of the schedule and the rate gains of coded caching
Fourth NASA Goddard Conference on Mass Storage Systems and Technologies
This report contains copies of all those technical papers received in time for publication just prior to the Fourth Goddard Conference on Mass Storage and Technologies, held March 28-30, 1995, at the University of Maryland, University College Conference Center, in College Park, Maryland. This series of conferences continues to serve as a unique medium for the exchange of information on topics relating to the ingestion and management of substantial amounts of data and the attendant problems involved. This year's discussion topics include new storage technology, stability of recorded media, performance studies, storage system solutions, the National Information infrastructure (Infobahn), the future for storage technology, and lessons learned from various projects. There also will be an update on the IEEE Mass Storage System Reference Model Version 5, on which the final vote was taken in July 1994
MediaSync: Handbook on Multimedia Synchronization
This book provides an approachable overview of the most recent advances in the fascinating field of media synchronization (mediasync), gathering contributions from the most representative and influential experts. Understanding the challenges of this field in the current multi-sensory, multi-device, and multi-protocol world is not an easy task. The book revisits the foundations of mediasync, including theoretical frameworks and models, highlights ongoing research efforts, like hybrid broadband broadcast (HBB) delivery and users' perception modeling (i.e., Quality of Experience or QoE), and paves the way for the future (e.g., towards the deployment of multi-sensory and ultra-realistic experiences). Although many advances around mediasync have been devised and deployed, this area of research is getting renewed attention to overcome remaining challenges in the next-generation (heterogeneous and ubiquitous) media ecosystem. Given the significant advances in this research area, its current relevance and the multiple disciplines it involves, the availability of a reference book on mediasync becomes necessary. This book fills the gap in this context. In particular, it addresses key aspects and reviews the most relevant contributions within the mediasync research space, from different perspectives. Mediasync: Handbook on Multimedia Synchronization is the perfect companion for scholars and practitioners that want to acquire strong knowledge about this research area, and also approach the challenges behind ensuring the best mediated experiences, by providing the adequate synchronization between the media elements that constitute these experiences
Building Efficient Software to Support Content Delivery Services
Many content delivery services use key components such as web servers, databases, and key-value stores to serve content over the Internet. These services, and their component systems, face unique modern challenges. Services now operate at massive scale, serving large files to wide user-bases. Additionally, resource contention is more prevalent than ever due to large file sizes, cloud-hosted and collocated services, and the use of resource-intensive features like content encryption. Existing systems have difficulty adapting to these challenges while still performing efficiently. For instance, streaming video web servers work well with small data, but struggle to service large, concurrent requests from disk. Our goal is to demonstrate how software can be augmented or replaced to help improve the performance and efficiency of select components of content delivery services.
We first introduce Libception, a system designed to help improve disk throughput for web servers that process numerous concurrent disk requests for large content. By using serialization and aggressive prefetching, Libception improves the throughput of the Apache and nginx web servers by a factor of 2 on FreeBSD and 2.5 on Linux when serving HTTP streaming video content. Notably, this improvement is achieved without changing the source code of either web server. We additionally show that Libception's benefits translate into performance gains for other workloads, reducing the runtime of a microbenchmark using the diff utility by 50% (again without modifying the application's source code).
We next implement Nessie, a distributed, RDMA-based, in-memory key-value store. Nessie decouples data from indexing metadata, and its protocol only consumes CPU on servers that initiate operations. This design makes Nessie resilient against CPU interference, allows it to perform well with large data values, and conserves energy during periods of non-peak load. We find that Nessie doubles throughput versus other approaches when CPU contention is introduced, and has 70% higher throughput when managing large data in write-oriented workloads. It also provides 41% power savings (over idle power consumption) versus other approaches when system load is at 20% of peak throughput.
Finally, we develop RocketStreams, a framework which facilitates the dissemination of live streaming video. RocketStreams exposes an easy-to-use API to applications, obviating the need for services to manually implement complicated data management and networking code. RocketStreams' TCP-based dissemination compares favourably to an alternative solution, reducing CPU utilization on delivery nodes by 54% and increasing viewer throughput by 27% versus the Redis data store. Additionally, when RDMA-enabled hardware is available, RocketStreams provides RDMA-based dissemination which further increases overall performance, decreasing CPU utilization by 95% and increasing concurrent viewer throughput by 55% versus Redis
Computer Science's Digest Volume 1
This series is dedicated to the students of the Systems Department, to give them reading material related to computer science in a second language. This book covers the Introduction to Computer Science, Computer Communications, Networking and Web Applications
Web design for effective online training and instruction.
The following is a research/experimental thesis that surveys and examines web-design for effective online training and instruction. The purpose of the thesis is to create -- from a variety of relevant learning theories and practical web-design strategies advocated in the research literature -- a Web-based instruction checklist that can be used to develop and assess online instructional materials. This checklist, referred to as WeBIC, is structured around the common ISD processes of analysis, design, development, implementation, and evaluation, with a focus on ‘Web Usability’ and ‘the Five Ps’ of preparation, presentation, participation, practice and performance. To determine the usefulness of WeBIC as a design and evaluation tool, three studies have been generated: (1) an experimental comparison study of online instructional materials in two formats -- a web-study one that follows guidelines and strategies outlined by WeBIC, and the other that follows a text-only format based on a modified form of thesis writing guidelines; (2) an analysis study of server data related to website access and instructional activity at ESLenglish.com and during the comparison study; and (3) an evaluation study of the instructional materials used in the comparison study and the instructional materials available at ESLenglish.com. The comparison study showed 2.1% learning gains that under closer analysis were found to be non-significant. The server analysis study confirmed the importance of designing for ‘speed of access’ and ‘navigation ease.’ It also brought into question the reliability of web mining data and the need for proper operational definitions. The evaluation study produced WeBIC scores for ESLenglish.com and the comparison study learning materials that could be used as benchmarks for further research
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