Abstract — The fairness issue in multi-player online games (MOGs) on deadline-based networks is investigated. A particular type of MOGs, namely the first-person-shooter (FPS) game, is examined. Potential unfair scenarios in FPS games due to disparate network delays are analyzed. A fairness definition and two fairness metrics are introduced. Two strategies to achieve fairness in FPS games on a deadline-based network are developed. The first strategy is based on end-system delay compensation; the other is based on the characteristics of the underlying network. The performance of the developed strategies is evaluated by simulation. Experiments show that by employing these two strategies, game fairness can be significantly improved. I.

Increasing demand to transmit real-time data over packet-switched networks calls for quality-of-service support from the underlying network. Deadline-based networks were developed for this purpose. In a deadline-based network, each application data unit (ADU) is associated with a delivery deadline, it is specified by the sending application and represents the time at which the ADU should be delivered at the receiver. The ADU deadline is mapped to packet deadlines, which are carried by packets and used by routers for channel scheduling; deadline- based scheduling is employed in routers. It was shown that a deadline-based network provides better support to real-time data delivery than a first-come-first-served network. We study how to effectively and efficiently deliver multimedia data in deadline- based networks, especially when at heavy load. When network load is high, congestion may occur. Multimedia data may miss their delivery deadlines due to excessive queueing delays and high packet loss ratios. This would directly affect the playback quality at the application layer. To control the level of load and improve performance, two end-system based admission control algorithms are developed. Their performance is evaluated using simulation. Both schemes are shown to improve the performance of multimedia delivery over deadline-based networks.

Multi-player online games have become very pop- ular in the last few years. Meanwhile, the IEEE 802.11 wireless networks have been in wide use. In this paper, we present an experimental study on the capability of an IEEE 802.11g network in supporting multi-player online games. In particular, we focus on the highly interactive first-person-shooter games. We describe the test bed we set up and the experiments we performed. Factors such as the number of game clients and the amount of background traffic are examined. Our results show that the amount of background traffic has a significant impact on the latency and the loss ratio of the game traffic between the game clients and the game server, which in turn affect the observed game performance greatly. I. INTRODUCTION

In deadline-based networks, the delay performance experienced by real-time data transfer largely depends on traffic deadlines and the load level along the data transfer path. To ensure fairness among users and to aid in network load control, a delay pricing and charging scheme was developed for realtime delivery in deadline-based networks; users experiencing different delay performance are charged differently and the charge is higher when the load is heavier. In response to an earlier charge, a price-sensitive adaptive application with limited budget constraints may adjust its traffic accordingly by varying traffic deadline requirements or traffic load intensity. We study the effect of application adaptation in two real-time traffic scenarios: discrete real-time documents, and a mixture of on-line game and multimedia traffic. We show through simulation that the aforementioned pricing and charging scheme easily enables user adaptation, which in turn may significantly improve the network delay performance.

Object abstraction supports the separation of what operations are provided by systems and components from how the operations are implemented, and is essential in enabling the construction of complex systems from components. Unfortunately, clear and modular implementations have poor performance when expensive query operations are repeated, while efficient implementations that incrementally maintain these query results are much more difficult to develop and to understand, because the code blows up significantly, and is no longer clear or modular.This paper describes a powerful and systematic method that first allows the "what" of each component to be specified in a clear and modular fashion and implemented straightforwardly in an object-oriented language; then analyzes the queries and updates, across object abstraction, in the straightforward implementation; and finally derives the sophisticated and efficient "how" of each component by incrementally maintaining the results of repeated expensive queries with respect to updates to their parameters. Our implementation and experimental results for example applications in query optimization, role-based access control, etc. demonstrate the effectiveness and benefit of the method.

In our deadline-based network resource management framework, each application data unit (ADU) is characterized by a (size, deadline) pair, which can be used to convey the resource and QoS requirements of the ADU. Specifically, the ADU's bandwidth requirement can be implicitly estimated by the ratio: size / (deadline - current time), and the time at which the ADU should be delivered is specified by the deadline. The ADU deadline is mapped onto deadlines at the network layer, which are carried by packets and used by routers for channel scheduling. In an earlier work, we have shown that deadline-based channel scheduling achieves good performance in terms of the percentage of ADUs that are delivered on-time. However, when a network is under heavy load, congestion may occur, and deadline-based scheduling alone may not be sufficient to prevent performance degradation. The level of congestion can be reduced by admission control. In this paper, two application-layer admission control algorithms are developed. The performance of these two algorithms is evaluated by simulation.

The use of deadline based channel scheduling in support of real time delivery of application data units (ADU's) is investigated. Of interest is priority scheduling where a packet with a smaller ratio of delivery deadline over number of hops to destination is given a higher priority. It has been shown that a variant of this scheduling algorithm, based on head-of-the-line priority, is efficient and effective in supporting real time delivery of ADU's. In this variant, packets with a ratio smaller than or equal to a given threshold are sent to the higher priority queue. We first present a technique to select this threshold dynamically. The effectiveness of our technique is evaluated by simulation. We then study the performance of deadline based channel scheduling for large networks, with multiple autonomous systems. For this case, accurate information on number of hops to destination may not be available. A technique to estimate this distance metric is presented. The effectiveness of our algorithm with this estimated distance metric is evaluated. In addition, we study the performance of a multi-service scenario where only a fraction of the routers deploy deadline based channel scheduling.

A novel approach to supporting real time applications in packet-switched networks is proposed. The key element of this approach is the use of a tuple (size, deadline) to characterize the performance requirements of a document. This tuple is mapped to deadline information at the network layer, which is carried in packets and used by routers for channel scheduling purposes. A new deadline based scheduling algorithm is developed. Simulation results show that this algorithm is superior to FCFS (first come first served) with respect to the percentage of documents that are delivered on time. Our scheduling algorithm is also efficient as far as implementation is concerned.