We present an integrated prefetching and caching proxy, termed iPac, for HTTP-based adaptive video streaming services like Netflix and YouTube. The challenge we address is maximizing the byte-hit ratio for proxies through prefetching in the context of the limited bandwidth between proxies and content servers. The problem is NP-hard, and the best approximation ratio that any optimal offline algorithm can achieve is 1-e--1 ≈ 0.63. Considering that offline algorithms cannot be applied to real-time applications with stringent time constraints, we propose a novel 0.5-competitive online prefetching algorithm which, to the best of our knowledge, has the best lower bound so far. We evaluate the performance of iPac by deploying it over the Amazon EC2 cloud accepting user requests from the video clients deployed on the PlanetLab based on a real trace of user requests for YouTube videos. Our experimental results demonstrate that iPac can significantly improve the performance in terms of byte-hit ratio (up to 84%) and video rates (up to 34%), compared with the state-of-the-art approaches. The proposed iPac is compatible with existing HTTP-based adaptive streaming implementations without requiring any modification to existing content servers and video clients.

One type of Peer-to-Peer (P2P) live streaming has not yet been significantly investigated, namely topologies that provide many-to-many, interactive connectivity. Exemplar applications of such P2P systems include spatial audio services for networked virtual environments (NVEs) and distributed online games. Numerous challenging problems have to be overcome-among them providing low delay, resilience to churn, effective load balancing, and rapid convergence-in such dynamic environments. We propose a novel P2P overlay dissemination mechanism, termed IDM, that can satisfy such demanding real-time requirements. Our target application is to provide spatialized voice support in multiplayer NVEs, where each bandwidth constrained peer potentially communicates with all other peers within its area-of-interest (AoI). With IDM each peer maintains a set of partners, termed helpers, which may act as stream forwarders. We prove analytically that the system reachability is maximized when the loads of helpers are balanced proportionally to their network capacities. We then propose a game-theoretic algorithm that balances the loads of the peers in a fully distributed manner. Of practical importance in dynamic systems, we prove that our algorithm converges to an approximately balanced state from any prior state in rapid O(\log \log n) time, where n is the number of users. We further evaluate our technique with simulations and show that it can achieve near optimal system reachability and satisfy the tight latency constraints of interactive audio under conditions of churn, avatar mobility, and heterogeneous user access network bandwidth.

We are interested to provide interactive spatial audio services for networked virtual environments (NVEs) in a peer-to-peer manner. The objective is to maximize the system reachability via efficiently utilizing the network capacities of users. We first propose a helper decomposition algorithm to construct an abstraction layer which consists of helpers formed by participating users. Each user selects a set of helpers that forward the audio streams on behalf of the user. We prove that the system reachability is Schur-concave on the loads of non-occupied helpers. We then propose a game-theoretic algorithm, termed water-fitting, to maximize the system reachability by rapidly balancing the loads of non-occupied helpers. The simulation results show that the proposed algorithms can achieve a near-optimal system reachability with respect to churn, avatar mobility and unpredictable speaking activity.

User-extensible metaverses need an effective way to disseminate massive and dynamic 3D contents (i.e., meshes, textures, animations, etc.) to end users, and at the same time maintain a low consumption of server bandwidth. Peer-to-peer (or peer-assisted) technologies have been widely considered as a desirable complementary solution to efficaciously offload servers in large-scale media streaming applications. However, due to both the bandwidth constraints of heterogeneous users and unpredictable access patterns of latency-sensitive 3D contents, it is very challenging to cut the server bandwidth cost in metaverses. In this paper, we propose a peer-assisted texture streaming architecture to minimize the server bandwidth consumption without degrading the end-user satisfaction. We propose a game-theoretic peer selection strategy which achieves a good trade-off between performance and complexity. Our algorithm is light-weight, and can efficiently utilize the bandwidth of users in a fully decentralized manner by enabling each peer (i.e., user) to quickly select its content providers who can satisfy the requests of the peer within the latency constraint of the content. We evaluate our algorithm through an extensive comparison study based on simulations using realistic data (i.e., avatar mobility traces and textures) collected from Second Life. The simulation results show that the proposed algorithm can effectively reduce the server bandwidth consumption without degrading the user experience.

In recent years, integrated spatialized voice services have become an appealing application for networked virtual environments (NVE), e.g., Second Life. With a spatialized voice service, people can identify who is talking if there are several participants in the vicinity. The key challenge in a spatialized audio streaming application is how to disseminate audio streams while observing bandwidth limits of end-user computers and tight latency constraints, and it can be modeled as NP-complete problem. In this paper, we propose a heuristic algorithm called CTA for spatialized audio streaming over NVEs in a peer-to-peer manner. The proposed algorithm was applied to real avatar mobility traces collected from Second Life, and the simulation results demonstrate that (a) CTA can achieve a high ratio of successful to candidate receivers and (b) CTA enables most of the successful receivers to enjoy minimum latency.

Networked virtual environments (NVE) are increasingly popular and represent a range of applications. Some online virtual worlds have a dedicated purpose, such as Massively Multiplayer Online Games (MMOG), while others implement more of foundational frameworks which are not necessarily applications per se, but form platforms to create applications. One of the premier examples of the latter is Second Life from Linden Lab. While such networked virtual environments show great potential for interesting and novel applications, many technical challenges remain. A significant shortcoming in current systems concerns the communication between virtual world participants. Early designs only supported text chat, while more recently voice chat has been introduced. However, often the voice communication paradigm still mimics traditional audio group conferencing without adaptation to the three-dimensional metaverse paradigm. In this study we present our design of an interactive audio streaming protocol that aims to enable the creation of an aural soundscape around the user that matches the visual experience. To make our design practical, scalable and to avoid further burdening the virtual world servers, our protocol is based on a peer-to-peer distribution topology. Simulation results are presented that show the feasibility and utility of our design.