Networked Graphics 01_P374423_PRELIMS.indd i 10/27/2009 6:57:42 AM

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1 Networked Graphics

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3 Networked Graphics Building Networked Games and Virtual Environments Anthony Steed Manuel Fradinho Oliveira AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Morgan Kaufmann Publishers is an imprint of Elsevier

4 Morgan Kaufmann Publishers is an imprint of Elsevier. 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA This book is printed on acid-free paper ELseviercompany. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data Application submitted British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN : For information on all Morgan Kaufmann publications, visit our Web site at or Printed in the United States of America

5 PART I GROUNDWORK CHAPTER 1 Introduction What are NVEs and NGs? The Illusion of a Shared Virtual Environment Some History Internet Simulators Multiuser Dungeons Electronic Games Virtual Reality Systems MMORPGs Social Spaces Scoping the Software Architecture Software Roles and Responsibilities Differences to Other Network Code Structure CHAPTER 2 One on One (101) Boids Boid Rules Standalone Implementation Distributed Boids: Concepts Distributed Boids: Implementation Revised Simulation and Data Model Network Concepts Network Protocol Implementation of the Network Component Sending UDP Data Packets Sending TCP Data Streams Reflection CHAPTER 3 Overview of the Internet The Internet Application Layer Application Layer Protocols Application QoS Common Applications and Ports RFCs DNS Telnet and HTTP v

6 vi 3.3 Transport Layer Implementing UDP Basics of TCP Reliability in TCP Opening and Closing TCP Connections Flow Control and Congestion Avoidance in TCP Network Layer Network Address Translation IP Packets Ping, Traceroute & ICMP Routing on the Internet DHCP Link and Physical Layer Ethernet Comparisons Further Network Facilities Multicast Network QoS Summary CHAPTER 4 More Than Two Boids Architecture Protocol Codebase Refactoring Simple Peer to Peer System Architecture Data Model Network Protocol Peer to Peer with Master System Architecture Datamodel Network Protocol Peer to Peer with Rendezvous Server System Architecture Datamodel Network Protocol Client/Server System Architecture Datamodel Network Protocol

7 vii 4.6 Multicast System Architecture Datamodel Network Protocol Extensions Protocol design Network Compensation Scale Binary Protocols Conclusions PART II FOUNDATIONS CHAPTER 5 Issues in Networking Graphics Architecture of the Individual System Engines and Engine Framework Modules Content Behavior Role of the Network Device I/O Sharing Data Model Sharing Command/Event Streaming Coping with Scale Initialization Case Study: Disney s Toontown Server and Peer Responsibilities Critical and Noncritical Synchronized or Unsynchronized Ownership and Locking Persistency Latency and Bandwidth Conclusions CHAPTER 6 Sockets and Middleware Role of Middleware Low-Level Socket APIs Main Functions Name Helper Functions and Options Network Byte Order Examples Socket Usage Patterns Windows

8 viii Synchronous I/O Critique and Discussion C and C Middleware for Networking HawkNL SDL_Net ACE Conclusion CHAPTER 7 Middleware and Message-Based Systems Message-Based Systems DIS PDUs X3D and DIS Basics of X3D Dataflow and Animation Scripting and Interfaces VRML/X3D Networking Strategies X3D and DIS X3D, HawkNL and DIS Sending a DIS Packet Receiving DIS Packets Conclusions CHAPTER 8 Middleware and Object-Sharing Systems Object-Sharing Systems RakNet Object Lifecycles Boids using Object-Sharing Boid Definitions Main Application Discussion General Object-Sharing Sharing Policy Visibility and Sampling Rates Ownership Scene-Graphs, Object-Sharing and Messages Conclusions CHAPTER 9 Other Networking Components Remote Method Call RPC XML-RPC, etc CORBA Discussion DIVE

9 ix DIVE Overview DIVE Entities Events Scripting and Event Scoping Networking Discussion System Architectures Conclusions PART III REAL SYSTEMS CHAPTER 10 Requirements Consistency System Perspective Plausibility & Fairness Consistency-Throughput Tradeoff Latency and Jitter Sources of Network Latency Jitter Clocks and Measurement of Latency and Jitter User Tolerance Latency Impact in Specific Systems Bandwidth Measurement Traffic Patterns Congestion State of the Internet Connectivity NAT Case Study: Burnout Paradise Car Mechanics Game Phases and Time Synchronization Game Hosting and Peer-to-Peer Networking Conclusions CHAPTER 11 Latency and Consistency Latency Impact Dumb Client and Lockstep Synchronization Dumb Client Lockstep Synchronization Conservative Simulations Time Optimistic Algorithms

10 x 11.6 Client Predict Ahead Extrapolation Algorithms Basic Dead-Reckoning Dead-Reckoning Variants Interpolation, Playout Delays and Local Lag Local Perception Filters Revealing Latency Conclusions CHAPTER 12 Scalability Service Architectures Awareness Cohorts, Groups and Service Architecture Overview of Interest Management Spatial Models Zone Models Dynamic Spatial Models Visibility Models Interest Specification and Interest Management Interest Expressions Interest Management Examples of Distributed Interest Management Separating Interest Management from Network Architecture Message Routing and Message Filtering Filtering as a Pipeline Routing and Filtering Examples Delegating Group Communication to the Network Layer Server Partitioning Server Tasks and Static Partitionings Seams and Handovers Load Balancing and Dynamic Partitioning Group Communication Services Reflectors and Tunnels Automatic Overlay Multicast Gossiping for Peer-to-Peer Communications Specific Group Communication Routing Service Peer to Peer Unstructured Peer-to-Peer Systems Structured Peer-to-Peer Systems Peer-to-Peer Support Using DHTs

11 xi Local Interest Systems Update-Free Regions and Frontier Sets Conclusions CHAPTER 13 Application Support Issues Security and Cheating Client-Side Attacks Network Level Server Side Social Repercussions Binary Protocols and Compression Binary Encodings Compression Streaming Audio and Video Geometry and Animation Mixing and Grouping Revisiting the Protocol Decision Persistent and Tiered Services Clusters Multidisplay Systems Massive Models Thin Clients Conclusions Index 489

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13 PART Groundwork I 1 Introduction One on One Overview of the Internet More Than Two