Shun-Yun Hu

VON: a scalable peer-to-peer network for virtual environments

The scalability of large-scale networked virtual environments (NVEs) such as todays massively multiplayer online games (MMOGs) faces inherent limits imposed by client-server architectures. We identify an emerging research direction that applies peer-to-peer (P2P) networks in order to realize more scalable and affordable NVEs. The central issue for P2P-based NVE (P2P-NVE) systems is to correctly and efficiently maintain the topology of all participating peers by solving the neighbor discovery problem. We also propose the Voronoi-based overlay network (VON), a simple and efficient design that maintains the P2P topology in a fully-distributed, low-latency, and message-efficient manner. Simulation results show that by bounding the per-node resource consumption, VON can be fundamentally more scalable than existing methods while achieving high topology consistency and reliability

Scalable peer-to-peer networked virtual environment

We propose a fully-distributed peer-to-peer architecture to solve the scalability problem of Networked Virtual Environment in a simple and efficient manner. Our method exploits locality of user interest inherent to such systems and is based on the mathematical construct Voronoi diagram. Scalable, responsive, fault-tolerant NVE can thus be constructed and deployed in an affordable way.

FLoD: A Framework for Peer-to-Peer 3D Streaming

Interactive 3D content on Internet has yet become popular due to its typically large volume and the limited network bandwidth. Progressive content transmission, or 3D streaming, thus is necessary to enable real-time content interactions. However, the heavy data and processing requirements of 3D streaming challenge the scalability of client-server delivery methods. We propose the use of peer-to-peer (P2P) networks for 3D streaming, and argue that due to the non-linear access patterns of 3D content, P2P 3D streaming is a new class of applications apart from existing media streaming and requires new investigations. We also present FLoD, the first P2P 3D streaming framework that allows clients of 3D virtual globe or virtual environment (VE) applications to obtain relevant data from other clients while minimizing server resource usage. To demonstrate how FLoD applies to real-world scenarios, we build a prototype system that adapts JPEG 2000-based 3D mesh streaming for P2P delivery. Experiments show that server-side bandwidth usage can thus be reduced, while simulations indicate that P2P 3D streaming is fundamentally more scalable than client-server approaches.

Scalable AOI-Cast for Peer-to-Peer Networked Virtual Environments

Networked virtual environments (NVEs) are computer-generated virtual worlds where users interact by exchanging messages via network connections. Each NVE user often pays attention to only a limited visibility sphere called area of interest (AOI) where interactions occur. The dissemination of messages to other users within the AOI (i.e., the AOI neighbors) thus is a fundamental NVE operation referred to as AOI-cast. Existing studies on NVE scalability have focused on system scalability, or the ability for the system to handle a growing number of total users, by using multicast or peer-to-peer (P2P) architectures. However, another overlooked, yet important form of scalability relates to the handling of a growing number of users within the AOI (or AOI scalability). In this paper, we propose two AOI-cast schemes, called VoroCast and FiboCast, to improve the AOI scalability of P2P-based NVEs. VoroCast constructs a spanning tree across all AOI neighbors based on Voronoi diagrams, while FiboCast dynamically adjusts the messaging range by a Fibonacci sequence, so that AOI neighbors would receive updates at frequencies based on their hop counts from the message originator. Simulations show that the two schemes provide better AOI scalability than existing approaches.

Selection strategies for peer-to-peer 3D streaming

In multi-user networked virtual environments such as Second Life, 3D streaming techniques have been used to progressively download and render 3D objects and terrain, so that a full download or prior installation is not necessary. As existing client-server architectures may not scale easily, 3D streaming based on peer-to-peer (P2P) delivery is recently proposed to allow users to acquire 3D content from other users instead of the server. However, discovering the peers who possess relevant data and have enough bandwidth to answer data requests is non-trivial. A naive query-response approach thus may be inefficient and could incur unnecessary latency and message overhead. In this paper, we propose a peer selection strategy for P2P-based 3D streaming, where peers exchange information on content availability incrementally with neighbors. Requestors can thus discover suppliers quickly and avoid time-consuming queries. A multi-level area of interest (AOI) request is also adopted to avoid request contention due to concentrated requests. Simulation results show that our strategies achieve better system scalability and streaming performance than a naive query-response approach.

Peer-to-Peer 3D Streaming

Virtual worlds have become very popular in recent years, with trends toward larger worlds and more user-generated content. The growth of 3D content in virtual worlds will make real-time content streaming (or 3D streaming) increasingly attractive for developers. To meet the demands of a large user base while lowering costs, peer-to-peer (P2P) content delivery holds the promise for a paradigm shift in how future virtual worlds will be deployed and used. The authors define both the problem and solution spaces for P2P 3D streaming - by outlining its requirements and challenges - and categorize existing proposals.

An efficient and secure event signature (EASES) protocol for peer-to-peer massively multiplayer online games

In recent years, massively multiplayer online games (MMOGs) have become very popular by providing more entertainment and sociability than single-player games. In order to prevent cheaters to gain unfair advantages in peer-to-peer (P2P)-based MMOGs, several cheat-proof schemes have been proposed by using digital signatures. However, digital signatures generally require a large amount of computations and thus may not be practical for interactive real-time applications such as games. Based on the concept of one-time signature, we propose an efficient and secure event signature (EASES) protocol to efficiently sign discrete event messages with hash-chain keys. As most messages need only two hash operations to achieve non-repudiation and event commitment, usage of digital signatures is greatly reduced. We also describe a dynamic version of EASES that does not require the pre-production of hash-chain keys to reduce key preparation time and memory usage at the expense of a slight delay of message commitment. As shown by both analysis and experiments, the computation, memory, and bandwidth footprints of EASES are low, making it readily applicable to P2P-based MMOGs.

A forwarding model for Voronoi-based Overlay Network

An approach to build highly scalable and robust networked virtual environments (NVEs) is using the peer-to-peer overlay networks. Voronoi-based overlay network (VON) has been proposed to maintain a highly overlay topology consistency in a bandwidth- efficient manner. However, the related research requires all nodes to connect directly with their relevant neighbors. This limits the number of neighbors should appear within the area of interest (AOI) of a given node. A new forwarding model for VON is proposed to solve this problem by connecting only with the nearest neighbors that is called the enclosing neighbors (EN), and propagating the position updates information to other nodes by message forwarding. In this way, the AOI of a given node may be more flexibly expanded and different bandwidth capacities may be more efficiently utilized.

Bandwidth-aware Peer-to-Peer 3D streaming

Peer-to-Peer streaming support for 3D content (i.e., P2P 3D streaming) has recently been proposed to provide affordable and real-time virtual environment (VE) content delivery. However, the generally limited client upload bandwidth requires maximal bandwidth utilization for effective streaming. This paper proposes Bandwidth-Aware Peer Selection (BAPS), a peer selection strategy that improves the bandwidth utilization for 3D streaming. BAPS avoids request contention and peer overloading as object and user densities increase, thus improving both bandwidth utilization and system scalability. We compare BAPS with strategies that select from only peers within the area of interest (AOI) as data sources and do not consider bandwidth capacity. Our evaluation shows that BAPS achieves better performance in general, and maintains a stable minimal quality of service (QoS) for streaming, which is important for commercial applications.

Enhancing Neighborship Consistency for Peer-to-Peer Distributed Virtual Environments

Although P2P-based DVEs can potentially solve the scalability issues, other important issues such as consistency remain unexplored. In this paper, we address neighborship consistency, which is the ratio between the number of known nodes and the number of actual nodes within a nodes area of interest (AOI). We address two factors that affect neighborship consistency for DVEs using Voronoi-based Overlay Network (VON). We propose adaptive AOI buffer and critical node detection to reduce the negative impacts of the two factors. We also perform simulation experiments to demonstrate the effects of the two factors before and after adopting the proposed mechanisms.