Contents LIST OF FIGURES...VIII LIST OF TABLES... X ABSTRACT...XI 1. INTRODUCTION... 1

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1 Contents LIST OF FIGURES...VIII LIST OF TABLES... X ABSTRACT...XI 1. INTRODUCTION COLLABORATIVE AUDIO THE SPECIFIC FOCUS OF THIS THESIS THESIS OVERVIEW AND CONTRIBUTIONS RELATED WORK CRITERIA Introduction Support for the most natural audio communication between users Support for maintaining acceptable audio quality Support for tailored audio presentations for each user Support for heterogeneous networks and end systems Support for efficient distribution of audio streams in the network Support for adaptation and fairness Overview of the Rest of the Chapter TECHNIQUES THAT DEAL WITH MANY SIMULTANEOUS SPEAKERS Introduction Floor-control Push-to-talk Silence Suppression Hardware Support - implicit floor control i

2 2.2.6 Open Microphones Discussion TECHNIQUES TO DEAL WITH EFFICIENT DISTRIBUTION OF AUDIO STREAMS IN NETWORK Introduction Techniques that affect single stream bandwidth Multicast Speech compression static (basic compression) Self-Organised Transcoding Scheme Filters Proxy services Discussion Techniques that affect multiple streams Mixing Architectures Centralised (total) mixing Client-specific Mixing Hierarchical Mixing Filtering and proxy services which perform mixing Real-time Protocol (RTP) Discussion RATE ADAPTATION TECHNIQUES Introduction Classification of congestion control mechanisms Rate-adaptation techniques with explicit feedback Adaptive Load Service (ALS) Bandwidth Adjustment Server (BWAS) Unicast-based rate adaptation techniques with implicit feedback Rate Adaptation Protocol (RAP) Direct Adjustment Algorithm (DAA) SCP Multimedia Transport Protocol (MTP) ii

3 TFRCP TFRC LDA Multicast-based rate adaptation techniques with implicit feedback Sender-based Receiver-driven Layered Multicast Congestion Control Discussion DISCUSSION DISTRIBUTED PARTIAL MIXING DISTRIBUTED PARTIAL MIXING (DPM) Partial Mixing An Overview Distributed Partial Mixing - An Overview Summary FUNCTIONAL MODEL Introduction Functional Stages Receiving audio streams and monitoring network resources Processing monitored resources/parameters Comparing available and required resources Selecting the streams to be mixed Mixing and/or Forwarding Transmitting and sending feedback and/or control information Summary MIXING CRITERIA EXAMPLE SPACE Mixing criteria driven by network Acceptable packet loss Congestion Control Fairness Network link limitation Mixing criteria driven by end system capabilities iii

4 Receiver processing characteristics Mixing criteria driven by application and user Pre-determined criteria Content of audio streams Voice characteristics Patterns of activity Receiver requirements Source requirements Stability considerations Summary SUMMARY IMPLEMENTATION AND EVALUATION INTRODUCTION SCENARIO AND INFRASTRUCTURE General scenario WAN Emulation Processing results DESIGN CHOICES Overview of Distributed Partial Mixing Realisation Monitoring and estimating packet loss rates Introduction What mechanism will be used for packet loss detection? What algorithm will be used for packet loss rate calculation? Where will packet loss detection and calculation happen? Monitoring and estimating round trip times (RTTs) Introduction What mechanism will be used for calculating RTT? Rate adaptation Introduction iv

5 What rate adaptation approach is used for distributed partial mixing? What is the increase/decrease policy of DPM? What is the decision frequency of DPM? (How) is self-limitation achieved? IMPLEMENTATION IN MASSIVE Platforms MASSIVE-3 audio service Overview of distributed partial mixing in MASSIVE DEMONSTRATION SCENARIO 1: DISTRIBUTED PARTIAL MIXING AND NON- ADAPTIVE TRAFFIC Approach Scenario and Infrastructure Results against non-adaptive traffic DEMONSTRATION SCENARIO 2: DISTRIBUTED PARTIAL MIXING AGAINST ADAPTIVE TRAFFIC Scenario and Infrastructure Results: TCP fairness Results: Demonstrating fairness between distributed partial mixing systems SUMMARY DEPLOYMENT INTRODUCTION STEADY-STATE LARGE SCALE DPM DEPLOYMENT Scenario and Infrastructure Issues in the steady-state large-scale DPM deployment DPM Topologies Echo and loops Delays Fan in and fan out / CPU load v

6 Tradeoffs Overview of the proposed tree topology Introduction Shared Trees Overview of other topologies Preventing loops and echoes Summary REALISING A LARGE SCALE DPM SERVICE OVER WANS Issues in realising large scale DPM service Deployment Domain DPM Placement DPM discovery and advertisement DPM initiation DPM topology determination Topology Control Support for re-configuration FULLY CENTRALISED DPM DEPLOYMENT OVER MANAGED NETWORKS SELF-ORGANISED DPM OVER UNMANAGED NETWORKS DISCUSSION Summary of the two proposals Discussion of other approaches to realizing DPM over WANs Deployment domain DPM Placement DPM initiation DPM discovery DPM topology determination Managing the process of topology determination Support for re-configuration SUMMARY vi

7 6. CONCLUSIONS SUMMARY CONTRIBUTIONS FUTURE WORK AND REFLECTIONS User and Application Modeling and Testing Real-world large scale experiments Differentiated and Integrated Services APPENDIX A REFERENCES vii

8 List of Figures FIGURE 2.1 LOGICAL MODEL OF PEER-TO-PEER VS. SERVER BASED APPROACHES FOR DISTRIBUTION OF AUDIO STREAMS FIGURE 3.1 SMALL-SCALE PARTIAL MIXING EXAMPLE FIGURE 3.2 INPUT AND OUTPUT OF A PARTIAL MIXING SYSTEM FIGURE 3.3 A TREE OF SOURCES, SINKS AND (PARTIAL) MIXERS FIGURE 3.4 FUNCTIONAL MODEL OF DISTRIBUTED PARTIAL MIXING FIGURE 3.5 SCHEME OF VARIOUS TYPES OF MIXING CRITERIA FIGURE 4.1 GENERAL DEMONSTRATION SCENARIO FIGURE 4.2 ARCHITECTURAL OVERVIEW OF DISTRIBUTED PARTIAL MIXING FIGURE 4.3 CALCULATING NETWORK DISTANCE FIGURE 4.4 AN EXAMPLE OF DISTRIBUTED PARTIAL MIXING IN MASSIVE FIGURE 4.5 EXPERIMENTAL SET-UP FIGURE 4.6 RATES OF PACKET LOSS AGAINST COMPETING (ADDITIONAL) TRAFFIC FIGURE 4.7 DEGREES OF SPATIALISATION (NUMBER OF INDEPENDENT AUDIO STREAMS) WITHIN TWO STANDARD DEVIATIONS AGAINST COMPETING TRAFFIC FIGURE 4.8 TEMPORAL BEHAVIOR OF DPM: RESPONSIVE AND STABLE DPM BEHAVIOR FIGURE 4.9 SELF-LIMITING BEHAVIOUR OF DPM FIGURE 4.10 TCP-FAIR AUDIO DISTRIBUTION SHOWING DETAILED BEHAVIOUR FIGURE 4.11 TCP-FAIR AUDIO DISTRIBUTION SHOWING MEDIUM TERM (SMOOTHED) BEHAVIOUR WITH COMPETING TCP FLOWS FIGURE 4.12 FAIR AUDIO DISTRIBUTION SHOWING MEDIUM TERM (SMOOTHED) BEHAVIOUR WITH COMPETING DPM AND TCP FLOW FIGURE 5.1 WIDE AREA DPM DEPLOYMENT FIGURE 5.2 AN EXAMPLE BIPARTITE GRAPH OF CLIENTS AND DPM SERVERS FIGURE 5. 3 INTERNAL LOGIC (STRUCTURE) OF A DPM SERVER WHEN DEALING WITH MULTIPLE LINKS FIGURE 5.4 STATIC CENTRALISED DPM SERVICE viii

9 FIGURE 5.5 SELF-ORGANISED DPM SERVICE FIGURE 5.6 PARTITIONING THE ORIGINAL MULTICAST GROUP INTO MULTICAST ISLANDS WHEN THE PROBLEMATIC LINK IS CONGESTED IN BOTH DIRECTIONS ix

10 List of Tables TABLE 2.1 TYPES OF CONTROL AND LEVEL OF SUPPORT FOR NATURAL AUDIO COMMUNICATION IN DIFFERENT TECHNIQUES THAT DEAL WITH MULTIPLE USERS 24 TABLE 2.2 OVERVIEW OF THE DISCUSSION OF THE TECHNIQUES THAT DEAL WITH EFFICIENT DISTRIBUTION OF AUDIO STREAMS TABLE 2.3 OVERVIEW OF THE DISCUSSION OF SOME OF THE RATE ADAPTATION TECHNIQUES IN TERMS OF TCP FAIRNESS, PACKET LOSS MANAGEMENT AND SUPPORT FOR HETEROGENEITY TABLE 3.1 FACTORS TO BE CONSIDERED FOR EACH FUNCTIONAL STAGE TABLE 5.1. RANGE OF EXAMPLE VALUES FOR MAXIMAL FAN IN/OUT AND HEIGHT OF THE TREE FOR VARIOUS NUMBERS OF CLIENTS TABLE 5.2 MULTICAST GROUPS USED FOR COMMUNICATION BETWEEN THE CLIENTS DIVIDED INTO TWO LOSS GROUPS ON THE OPPOSITE SIDES OF THE CONGESTED LINK TABLE 5.3 SUMMARISING THE CHOICES IN TERMS OF ISSUES FOR THE TWO GIVEN ILLUSTRATIONS TABLE 5.4 ADVANTAGES AND DISADVANTAGES OF HETEROGENEOUS DEPLOYMENT DOMAINS TABLE 5.5 ADVANTAGES AND DISADVANTAGES OF VARIOUS PLACEMENT SCHEMES. 158 TABLE 5.6 ADVANTAGES AND DISADVANTAGES OF VARIOUS DPM INITIATION SCHEMES TABLE 5.7 ADVANTAGES AND DISADVANTAGES OF DISCOVERY MECHANISES TABLE 5.8 ADVANTAGES AND DISADVANTAGES OF VARIOUS TOPOLOGY DETERMINATION SCHEMES TABLE 5.9 ADVANTAGES AND DISADVANTAGES OF VARIOUS TOPOLOGY CONTROL MECHANISMS TABLE 5.10 ADVANTAGES AND DISADVANTAGES OF SUPPORT FOR RE-CONFIGURATION OF VARIOUS TOPOLOGIES x