Reliability Analysis of the Hypercube Architecture.

This dissertation presents improved techniques for analyzing network-connected (NCF), 2-connected (2CF), task-based (TBF), and subcube (SF) functionality measures in a hypercube multiprocessor with faulty processing elements (PE) and/or communication elements (CE). These measures help study system-level fault tolerance issues and relate to various application modes in the hypercube. Solutions discussed in the text fall into probabilistic and deterministic models. The probabilistic measure assumes a stochastic graph of the hypercube where PE\u27s and/or CE\u27s may fail with certain probabilities, while the deterministic model considers that some system components are already failed and aims to determine the system functionality. For probabilistic model, MIL-HDBK-217F is used to predict PE and CE failure rates for an Intel iPSC system. First, a technique called CAREL is presented. A proof of its correctness is included in an appendix. Using the shelling ordering concept, CAREL is shown to solve the exact probabilistic NCF measure for a hypercube in time polynomial in the number of spanning trees. However, this number increases exponentially in the hypercube dimension. This dissertation, then, aims to more efficiently obtain lower and upper bounds on the measures. Algorithms, presented in the text, generate tighter bounds than had been obtained previously and run in time polynomial in the cube dimension. The proposed algorithms for probabilistic 2CF measure consider PE and/or CE failures. In attempting to evaluate deterministic measures, a hybrid method for fault tolerant broadcasting in the hypercube is proposed. This method combines the favorable features of redundant and non-redundant techniques. A generalized result on the deterministic TBF measure for the hypercube is then described. Two distributed algorithms are proposed to identify the largest operational subcubes in a hypercube C\sb{n} with faulty PE\u27s. Method 1, called LOS1, requires a list of faulty components and utilizes the CMB operator of CAREL to solve the problem. In case the number of unavailable nodes (faulty or busy) increases, an alternative distributed approach, called LOS2, processes m available nodes in O(mn) time. The proposed techniques are simple and efficient

A memory efficient algorithm for network reliability

We combine the Augmented Ordered Binary Decision Diagram (OBDD-A) with the use of boundary sets to create a method for computing the exact K-terminal or all-terminal reliability of an undirected network with failed edges and perfect vertices. We present the results of implementing this algorithm and show that the execution time is comparable with the state of the art and the space requirement is greatly reduced. Indeed the space remains constant when networks increase in size but maintain their structure and maximum boundary set size; with the same amount of memory used for computing a 312 and a 31000 grid network

A survey on network game cheats and P2P solutions

The increasing popularity of Massively Multiplayer Online Games (MMOG) - games involving thousands of players participating simultaneously in a single virtual world - has highlighted the scalability bottlenecks present in centralised Client/Server (C/S) architectures. Researchers are proposing Peer-to-Peer (P2P) game technologies as a scalable alternative to C/S; however, P2P is more vulnerable to cheating as it decentralises the game state and logic to un-trusted peer machines, rather than using trusted centralised servers. Cheating is a major concern for online games, as a minority of cheaters can potentially ruin the game for all players. In this paper we present a review and classification of known cheats, and provide real-world examples where possible. Further, we discuss counter measures used by C/S game technologies to prevent cheating. Finally, we discuss several P2P architectures designed to prevent cheating, highlighting their strengths and weaknesses

Adaptive Client to Mirrored-Server Assignment for Massively Multiplayer Online Games

The Mirrored Server (MS) architecture for network games uses multiple mirrored servers across multiple locations to alleviate the bandwidth bottleneck and to reduce the client-to-server delay time. Response time in MS can be reduced by optimally assigning clients to their mirrors. The goal of optimal client-to-mirror-assignment (CMA) is to achieve the minimum average client-to-mirror delay considering player joins (CMA-J) and leaves (CMA-L), and mirrors with limited capacity. The existing heuristic solution considers only CMA-J, and thus the average delay of the remaining players may increase when one or more players leave. Furthermore, the solution ignores mirror capacity, which may overload mirrors. In this paper we present a resource usage model for the MS architecture, and formally state the CMA problem. For both CMA-J and CMA-L we propose a polynomial time optimal solution and a faster heuristic algorithm that obtains near optimal CMA. Our simulations on randomly generated MS topologies show that our algorithms significantly reduce the average delay of the existing solution. We also compare the merits of the solutions in terms of their optimality and running time efficiency

Round length optimisation for P2P network gaming

The Referee Anti-Cheat Scheme (RACS) increases the scalability of Client/Server (C/S) games by allowing clients to exchange updates directly. Further, RACS maintains the security of C/S as the trusted referee (running on the server) is the game authority, simulating all client updates to validate the simulation. In RACS time is divided into rounds, and every player generates one update per round. The round length d is bounded by dmax which is specified by the game developer. The referee may reduce d to increase game responsiveness for players. Existing approaches to adjust d require purely distributed algorithms as they do not have a trusted central authority. These algorithms are slow and use considerable bandwidth. In this paper we propose a delay model for RACS, and two centralised algorithms to calculate d for maximum responsiveness - an optimal brute force approach and an efficient voting algorithm. We use simulation to show that the voting algorithm produces nearly optimal results, and analytical analysis to show that its processing requirements are far lower than the brute force approach

Cheating in networked computer games: a review

The increasing popularity of Massively Multiplayer Online Games (MMOG) - games involving thousands of players participating simultaneously in a single virtual world - has highlighted the scalability bottlenecks present in centralised Client/Server (C/S) architectures. Researchers are proposing Peer-to-Peer (P2P) architectures as a scalable alternative to C/S; however, P2P is more vulnerable to cheating as it decentralises the game state and logic to un-trusted peer machines, rather than using trusted centralised servers. Cheating is a major concern for online games, as a minority of cheaters can potentially ruin the game for all players. In this paper we present a review and classification of known cheats, and provide real-world examples where possible. Further, we discuss counter measures used by C/S architectures to prevent cheating. Finally, we discuss several P2P architectures designed to prevent cheating, highlighting their strengths and weaknesses

NGS: An application layer network game simulator

In the last five years the popularity of Massively Multiplayer Online Games (MMOGs) has exploded. Unfortunately, the demand has far outweighed the resources developers can provide. Many MMOGs are suffering from scalability issues, resulting in sharding, down time, and server crashes. To solve these problems, the research community is investigating peer-to-peer (P2P) overlay networks to support MMOGs, as P2P networks are theoretically and practically scalable. The majority of analysis of P2P gaming architectures has been qualitative, making it difficult to understand the strengths and weaknesses of each system. This is partially due to the lack of appropriate simulation tools. To address this problem we have developed an application layer network game simulator - NGS - for modelling network game architectures. NGS includes mechanisms to collect quantitative metrics, which may then be used to perform comparisons with other architectures. NGS is flexible enough to model Client/Server, Region based, Neighbour based, and hybrid architectures. It is extensible and modular, and will enable the research community to evaluate the benefits and weaknesses of existing and new network gaming architectures. Results demonstrating the extensibility and performance of NGS, and comparisons of the performance of several different architectures are included