UNIVERSIDADE FEDERAL FLUMINENSE CENTRO TECNOLÓGICO MESTRADO EM ENGENHARIA DE TELECOMUNICAÇÕES RICARDO CAMPANHA CARRANO IMPROVING THE SCALABILITY AND RELAIBILITY OF THE XO MESH NETWORK NITERÓI 2008 i RICARDO CAMPANHA CARRANO IMPROVING THE SCALABILITY AND RELAIBILITY OF THE XO MESH NETWORK Dissertação apresentada ao Curso de Mestrado em Engenharia de Telecomunicações da Universidade Federal Fluminense, como requisito parcial para obtenção do Grau de Mestre. Área de Concentração: Sistemas de Telecomunicações Orientador: Prof o Luiz Cláudio Schara Magalhães, Phd NITERÓI 2008 ii RICARDO CAMPANHA CARRANO IMPROVING THE SCALABILITY AND RELAIBILITY OF THE XO MESH NETWORK Dissertação apresentada ao Curso de Mestrado em Engenharia de Telecomunicações da Universidade Federal Fluminense, como requisito parcial para obtenção do Grau de Mestre. Área de Concentração: Sistemas de Telecomunicações Aprovada em Dezembro de 2008 BANCA EXAMINADORA ________________________________________________________ Prof. Dr. LUIZ CLAUDIO SCHARA MAGALHÃES ________________________________________________________ Prof. Dr. MICHAEL ANTHONY STANTON ________________________________________________________ Prof. Dr. ANTÔNIO JORGE GOMES ABELÉM iii This work is dedicated to all people that work for improving the life of others. May all children have access to good education and through knowledge achieve peace and happiness . iv ACKNOWLEDGEMENTS / AGRADECIMENTOS First, I would like to thank my advisor Luiz Claudio Schara Magalhães for his guidance and for all the exciting opportunities I have enjoyed as his student. I also thank the teachers, colleagues and staff at the Masters Program of the Telecommunications Engineering Department at Universidade Federal Fluminense , especially Professors Célio Vinicius Neves de Albuquerque and Débora Cristina Muchaluat Saade and all my friends at Midiacom . I have the deepest gratitude for the continuous support and inspiration from my boss at One Laptop per Child , Michalis Bletsas. Special thanks to him and to everyone at OLPC . Many, many thanks are due to Javier Cardona , Luis Carlos Cobo and Brian Cavagnolo and everyone at CozyBit; and Ashish Shukla, Rajesh Bhagwat , Shailendra Govardhan and Ronak Chokshi at Marvell for their generosity in promptly answering my copious questions. Last, but not least, I thank my precious wife Erika , for her love and support; my father Jorge and my mother Wanda for giving me the tools to make the best of my life. This work was partially funded by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), RNP (Rede Nacional de Ensino e Pesquisa) and by One Laptop Per Child . v TABLE OF CONTENTS LIST OF FIGURES....................................................................................................................... viii LIST OF TABLES ............................................................................................................................x LIST OF ABBREVIATIONS.......................................................................................................... xi RESUMO...................................................................................................................................... xiv ABSTRACT....................................................................................................................................xv 1. INTRODUCTION ........................................................................................................................ 1 1.1. OVERVIEW ..................................................................................................................... 1 1.2. MOTIVATION AND OBJECTIVES ...................................................................................... 3 1.3. WORK ORGANIZATION ................................................................................................... 4 1.4. THE RUCA PROJECT ...................................................................................................... 4 1.5. OLPC AND THE XO ....................................................................................................... 7 2. IEEE802.11 WIRELESS NETWORKS ........................................................................................ 11 2.1. OVERVIEW ................................................................................................................... 11 2.2. THE PHYSICAL LAYER .................................................................................................. 12 2.3. MEDIUM ACCESS CONTROL ......................................................................................... 14 2.4. 802.11 FRAME FORMAT ................................................................................................ 18 2.5. TYPES OF 802.11 NETWORKS ....................................................................................... 21 3. MANET S (M OBILE AD-HOC NET WORKS )............................................................................ 25 3.1. INTRODUCTION ............................................................................................................ 25 3.2. ROUTING PROTOCOLS .................................................................................................. 28 3.3. PROACTIVE PROTOCOLS ............................................................................................... 28 3.4. REACTIVE PROTOCOLS ................................................................................................. 30 3.5. HYBRID PROTOCOLS .................................................................................................... 31 3.6. METRICS ...................................................................................................................... 33 4. IEEE802.11 S......................................................................................................................... 35 4.1. INTRODUCTION ............................................................................................................ 35 4.2. MULTIHOP -MAC MESH NETWORK ARCHITECTURE .................................................... 36 4.3. MESH CREATION .......................................................................................................... 37 4.4. PATH SELECTION MECHANISMS ................................................................................... 39 4.5. HWMP AND AIRTIME LINK METRIC ........................................................................... 40 4.6. INTERNETWORKING WITH 802.11 S............................................................................... 44 4.7. FRAME STRUCTURE AND SYNTAX ................................................................................ 46 4.8. STA S CONNECTIVITY AND FRAME ADDRESSING .......................................................... 48 4.9. ADDITIONAL FEATURES ............................................................................................... 51 5. THE OLPC IMPLEMENTATION ............................................................................................... 53 5.1. DIFFERENCES TO IEEE802.11 S.................................................................................... 53 5.1.1. PATH ASYMMETRY ................................................................................................. 53 5.1.2. METRICS ................................................................................................................ 54 5.1.3. THE PATH DISCOVERY MECHANISM IN DETAIL ....................................................... 54 5.2. NON IMPLEMENTED FEATURES ..................................................................................... 57 5.2.1. LINK ESTABLISHMENT ............................................................................................ 57 5.2.2. SECURITY ............................................................................................................... 58 5.2.3. MEDIUM ACCESS PROTOCOL .................................................................................. 58 5.2.4. CONGESTION CONTROL ......................................................................................... 58 5.2.5. POWER SAVINGS MODE .......................................................................................... 58 5.3. IMPLEMENTATION DETAILS.......................................................................................... 58 5.3.1. FORWARDING TABLE .............................................................................................. 59 5.3.2. BLINDING TABLE .................................................................................................... 60 5.3.3. AVOIDING DUPLICATES ......................................................................................... 60 vi 5.3.4. CONFIGURABLE PARAMETERS ................................................................................ 61 6. ANALYSES AND PROPOSED OPTIMIZATIONS ........................................................................... 63 6.1. INTRODUCTION ............................................................................................................ 63 6.2. METHODOLOGY AND TESTBED .................................................................................... 64 6.3. ANALYSIS 1 – AIRTIME CONSUMPTION ........................................................................ 64 6.3.1. BEACON BACKOFF ................................................................................................. 65 6.3.2. PROBE REQUESTS /P ROBE RESPONSES ...................................................................