Design, analysis, and experimental verification of continuous media retrieval and caching strategies for network-based multimedia services

Ph.DDOCTOR OF PHILOSOPH

Sixth Goddard Conference on Mass Storage Systems and Technologies Held in Cooperation with the Fifteenth IEEE Symposium on Mass Storage Systems

This document contains copies of those technical papers received in time for publication prior to the Sixth Goddard Conference on Mass Storage Systems and Technologies which is being held in cooperation with the Fifteenth IEEE Symposium on Mass Storage Systems at the University of Maryland-University College Inn and Conference Center March 23-26, 1998. As one of an ongoing series, this Conference continues to provide a forum for discussion of issues relevant to the management of large volumes of data. The Conference encourages all interested organizations to discuss long term mass storage requirements and experiences in fielding solutions. Emphasis is on current and future practical solutions addressing issues in data management, storage systems and media, data acquisition, long term retention of data, and data distribution. This year's discussion topics include architecture, tape optimization, new technology, performance, standards, site reports, vendor solutions. Tutorials will be available on shared file systems, file system backups, data mining, and the dynamics of obsolescence

Load Sharing in Distributed Multimedia-on-Demand Systems

10.1109/69.846293IEEE Transactions on Knowledge and Data Engineering123410-428ITKE

Cheating Prevention in Peer-to-Peer-based Massively Multiuser Virtual Environments

Massively multiuser virtual environments (MMVEs) have become an increasingly popular Internet application in recent years. Until now, they are all based on client/server technology. Due to its inherent lack of scalability, realizing MMVEs based on peer-to-peer technology has received a lot of interest. From the perspective of the operator, using peer-to-peer technology raises additional challenges: the lack of trust in peers and their unreliability. The simulation of the virtual environment is governed by certain rules specified by the operator. These rules state what actions can be taken by users in the virtual environment and how the state of the environment changes based on these actions. Since MMVEs are very often competitive environments, some people will cheat and try to break the rules to get an unfair advantage over others. Using a central server performing the simulation of the virtual environment, the operator can ensure only allowed actions can be performed and the state of the environment evolves according to the rules. In a peer-to-peer setting, the operator has no control over the peers so they might not behave as implemented by the operator. Furthermore, a central server is inherently more reliable than a peer which could fail at any time so data might be lost. This thesis presents the design of a storage performing a distributed simulation of a virtual environment. It uses a deterministic event-based simulation to calculate the state of the virtual environment only based on the actions of its users. There are multiple replicated simulations using a voting mechanism to overcome the influence of malicious peers trying to tamper with the state of the environment as long as the number of malicious peers does not reach a critical threshold. Replication of data also ensures data is not lost when peers fail. The storage is based on a peer-to-peer overlay allowing peers to exchange messages to store and retrieve data. It creates a Delaunay graph structure matching the way the data in the virtual environment is distributed among the peers. A self-stabilizing algorithm keeps the structure intact as peers join and leave the network. Additional routing tables allow peers to retrieve stored replicas independently on short, disjoint paths reducing the influence of malicious peers on the retrieval of data. A redundant filling algorithm prevents malicious peers from tampering with these routing tables to get more messages routed their way

Satellite Networks: Architectures, Applications, and Technologies

Since global satellite networks are moving to the forefront in enhancing the national and global information infrastructures due to communication satellites' unique networking characteristics, a workshop was organized to assess the progress made to date and chart the future. This workshop provided the forum to assess the current state-of-the-art, identify key issues, and highlight the emerging trends in the next-generation architectures, data protocol development, communication interoperability, and applications. Presentations on overview, state-of-the-art in research, development, deployment and applications and future trends on satellite networks are assembled

Information-centric communication in mobile and wireless networks

Information-centric networking (ICN) is a new communication paradigm that has been proposed to cope with drawbacks of host-based communication protocols, namely scalability and security. In this thesis, we base our work on Named Data Networking (NDN), which is a popular ICN architecture, and investigate NDN in the context of wireless and mobile ad hoc networks. In a first part, we focus on NDN efficiency (and potential improvements) in wireless environments by investigating NDN in wireless one-hop communication, i.e., without any routing protocols. A basic requirement to initiate informationcentric communication is the knowledge of existing and available content names. Therefore, we develop three opportunistic content discovery algorithms and evaluate them in diverse scenarios for different node densities and content distributions. After content names are known, requesters can retrieve content opportunistically from any neighbor node that provides the content. However, in case of short contact times to content sources, content retrieval may be disrupted. Therefore, we develop a requester application that keeps meta information of disrupted content retrievals and enables resume operations when a new content source has been found. Besides message efficiency, we also evaluate power consumption of information-centric broadcast and unicast communication. Based on our findings, we develop two mechanisms to increase efficiency of information-centric wireless one-hop communication. The first approach called Dynamic Unicast (DU) avoids broadcast communication whenever possible since broadcast transmissions result in more duplicate Data transmissions, lower data rates and higher energy consumption on mobile nodes, which are not interested in overheard Data, compared to unicast communication. Hence, DU uses broadcast communication only until a content source has been found and then retrieves content directly via unicast from the same source. The second approach called RC-NDN targets efficiency of wireless broadcast communication by reducing the number of duplicate Data transmissions. In particular, RC-NDN is a Data encoding scheme for content sources that increases diversity in wireless broadcast transmissions such that multiple concurrent requesters can profit from each others’ (overheard) message transmissions. If requesters and content sources are not in one-hop distance to each other, requests need to be forwarded via multi-hop routing. Therefore, in a second part of this thesis, we investigate information-centric wireless multi-hop communication. First, we consider multi-hop broadcast communication in the context of rather static community networks. We introduce the concept of preferred forwarders, which relay Interest messages slightly faster than non-preferred forwarders to reduce redundant duplicate message transmissions. While this approach works well in static networks, the performance may degrade in mobile networks if preferred forwarders may regularly move away. Thus, to enable routing in mobile ad hoc networks, we extend DU for multi-hop communication. Compared to one-hop communication, multi-hop DU requires efficient path update mechanisms (since multi-hop paths may expire quickly) and new forwarding strategies to maintain NDN benefits (request aggregation and caching) such that only a few messages need to be transmitted over the entire end-to-end path even in case of multiple concurrent requesters. To perform quick retransmission in case of collisions or other transmission errors, we implement and evaluate retransmission timers from related work and compare them to CCNTimer, which is a new algorithm that enables shorter content retrieval times in information-centric wireless multi-hop communication. Yet, in case of intermittent connectivity between requesters and content sources, multi-hop routing protocols may not work because they require continuous end-to-end paths. Therefore, we present agent-based content retrieval (ACR) for delay-tolerant networks. In ACR, requester nodes can delegate content retrieval to mobile agent nodes, which move closer to content sources, can retrieve content and return it to requesters. Thus, ACR exploits the mobility of agent nodes to retrieve content from remote locations. To enable delay-tolerant communication via agents, retrieved content needs to be stored persistently such that requesters can verify its authenticity via original publisher signatures. To achieve this, we develop a persistent caching concept that maintains received popular content in repositories and deletes unpopular content if free space is required. Since our persistent caching concept can complement regular short-term caching in the content store, it can also be used for network caching to store popular delay-tolerant content at edge routers (to reduce network traffic and improve network performance) while real-time traffic can still be maintained and served from the content store

Modeling and acceleration of content delivery in world wide web

Ph.DDOCTOR OF PHILOSOPH

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