Signaling for conferencing in mobile ad hoc networks

Mobile Ad hoc NETworks (MANETs) are networks that do not need to be pre-configured. They are composed of transient nodes connected through wireless interfaces. Due to their flexibility, the ease to build and the associated low cost, they are gaining more and more momentum. They are also seen as part of the fourth generation wireless networks. New applications, such as conferencing, are emerging for such networks. Conferencing enables a set of applications such as audio/video conferencing, debating, distance-learning and multi-party gaming. The implementation of conferencing in MANETs is not an easy task due to scarce network resources, heterogeneous devices, frequently changing topology and unstable wireless connections. It challenges each technical aspect of conferencing: signaling, media handling and conference control. Signaling is the control component of conferencing. It handles the session initiation, modification and termination. In this work, we focus on signaling for conferencing in MANETs. Two types of MANETs are considered: standalone MANETs and integrated MANETs/3G networks. Background information is provided, requirements are derived and the state of the art, including signaling protocols such as SIP and H.323, are reviewed. Since there is no existing solution that meets all of the derived requirements, we propose a novel cluster-based signaling architecture that meets the requirements of signaling for standalone MANETs. The clusters are application-layer clusters that are dynamically created and deleted for a conference. We also propose a signaling architectures for integrated MANETs/3G networks. The solution is based on conference gateways. We implement the architectures using SIP extensions. Experimental results are obtained from prototypes and OPNET based simulations. In the prototype, we built the signaling system on a small scale network using IEEE 802.11 ad hoc settings. In the OPNET simulation, we use MANET features. From experiments, we found that clustering is a very promising approach for solving signaling problems in MANETs. Being aware of several performance issues of our signaling systems, we further propose optimization schemes that are based on cross-layer design. We also implement some of these schemes and apply them to our signaling systems. The evaluation shows that the schemes significantly improve the signaling performance

MECHANISMS FOR ENHANCING THE DEPENDABILITY OF WIRELESS AD-HOC NETWORKS

隨著無線通訊和微機電技術的快速發展，無線移動隨意網路的應用亦逐漸成形；此種網路與生俱來的機動性與彈性使其在特定的領域具有深遠的潛力，例如軍事科技或是災難救援任務。然而在工程上，我們將面臨眾多在提高系統可靠度 (dependability) 與擴展度 (scalability) 上的挑戰，由於此種網路易於缺乏如頻寬或電源等重要系統資源，加上因不具實體的基礎建設而導致網路拓樸結構的不穩定，這些特性都使有關可靠度的議題變得非常棘手。基本上，在設計運作於此種網路的系統時，必需掌握分散式以及只依賴區域性資訊的原則；如此我們將可便於維持某種虛擬的基礎建設，並依此來趨近所欲達成的目標。另一方面，為了應付各式各樣、不知何時會發生的網路原件故障或暫時失效，需導入隨機演算法 (randomized algorithms) 與動態調適 (adaptive)的概念，因為根據相關的文獻顯示，這些概念在行動計算環境中可以有效地增強系統對於錯誤的包容力 (fault tolerance) 和恢復力 (resilience)。 在本論文中，我們研究目的在於提高無線移動隨意網路可靠度。我們主要所採取的方法在於對網路由下而上的數個層面提供特定的容錯機制，經由過往的研究報告和實驗得知，不同網路層面間的行為互動往往對此種網路的效能帶來重大影響。具體來說，我們將重心放在 (1) 網路拓樸控制 (topology control)；(2) 錯誤偵測服務 (failure detection)；(3) 資料的可取得性 (data accessibility)；(4) 系統自行修復能力 (self-repair capacity)。而設計各種機制的主要依據為上段所描述的原理。在每一章節中我們分別對於所提供的機制進行模擬實驗或是數學分析以驗證其效能，而結果均能滿足我們在系統可靠度上欲提高的量測項目 (performance metrics)。我們亦針對各個主題爬梳最新最具潛力的文獻和值得深入探討之方向，冀能激發更創新的研究想法。未來最重要的工作是測試在量產化的機台上整合各網路層面機制後所能獲得的實質效能改善。The advent of wireless ad-hoc networks poses lots of new challenges in the provision of system dependability and scalability. On one hand, these networks are drawing substantial attention in the research community because of their various potential applications. On the other hand, their primary characteristics include scarce resources (e.g., bandwidth, battery power, etc.), a dynamic changing topology, and lack of any physical backbone infrastructureTABLE OF CONTENTS LIST OF FIGURES iii LIST OF TABLES v ABSTRACT vii CHAPTERS 1 INTRODUCTION AND OVERVIEW 1 2 POWER-EFFICIENT TOPOLOGY CONTROL ALGORITHMS 5 2.1 Motivation 6 2.2 Related Works 9 2.3 Method 11 2.3.1 Observations 11 2.3.2 Two-Phase Localized Algorithm 13 2.3.3 Heuristics to Improve the Performance 18 2.3.4 Properties of the Constructed Topology 19 2.4 Performance Comparisons 21 2.5 Discussion 29 2.5.1 On Negligible Receiver Power 29 2.5.2 Dealing with Mobility 30 2.6 Summary 33 3 COMMUNICATION STRATEGIES FOR HEARTBEAT-STYLE FAILURE DETECTORS IN WIRELESS AD-HOC NETWORKS 35 3.1 Motivation 36 3.2 Related Works 40 3.3 Model 42 3.4 Preliminaries 43 3.5 Linear Solution 45 3.6 Transient Hierarchical Solution 46 3.6.1 Observations 46 3.6.2 Two-Phase Gossiping 49 3.6.3 Heuristics for Further Improvement 52 3.7 Simulation Results 53 3.8 Discussion 60 3.9 Summary 61 4 ENHANCING DATA AVAILABILITY 63 4.1 Motivation 64 4.2 Background 65 4.2.1 Preliminaries 65 4.2.2 Observations 65 4.3 Hardness Results 68 4.3.1 Replica Placement 69 4.3.2 Retrieval Sequence 72 4.4 Science of Networks 74 4.5 Discussion 76 4.6 Summary 78 5 RANDOMIZED DISTRIBUTED METHODS FOR SELF-REPAIR 79 5.1 Motivation 80 5.2 Preliminaries 81 5.3 Model and Problem Formulation 84 5.4 Method 85 5.4.1 A Simple Randomized Rerouting Scheme 85 5.4.2 Analysis of the Simple Scheme 90 5.4.3 Toward Multiple-Repair 92 5.5 Discussion 94 5.5.1 Convergence Conditions 94 5.5.2 Practical Implications 95 5.6 Summary 96 6 CONCLUDING REMARKS AND FUTURE DIRECTIONS 98 BIBLIOGRAPHY 101 PUBLICATION LIST 10