ACM MobiWac 2006 Message from the Chairs It is our great pleasure to welcome you to the 4th ACM International Workshop on Mobility Management and Wireless Access – MobiWac 2006. Continuing the tradition of previous MobiWac editions in Forth Worth (TX), Philadelphia (PA) and Maui (Hawaii), this year’s workshop testifies the maturation, relevance and interest on mobility management and wireless access research activities. The workshop is a forum for the discussion and presentation of original ideas, recent results and achievements by researchers, students, and system developers on issues and challenges related to mobility management and wireless access, at many layers and under different technology viewpoints. The mission of the workshop is to give researchers and practitioners a unique opportunity to share and enlarge their perspectives and ideas with others, by enjoying a stimulating program. The call for papers attracted more than 60 submissions from Asia, Canada, Europe, Africa, and the United States. The program committee accepted 18 papers, which represent a 30% acceptance rate, and cover a variety of topics, including wireless and mobile broadband access, wireless ad hoc, vehicular, mesh and sensor networks, next generation wireless systems, wireless Internet access, mobility control and management, mobile services, QoS management, localization and tracking, channel and resource allocation, context-aware services and applications, energy and power management. In addition, the program includes a poster session that will host more than 10 relevant paper contributions on the same topics. The accepted papers are from 17 countries (US, Canada, Taiwan, Greece, Germany, Spain, Japan, Portugal, Brasil, Australia, Korea, Italy, United Kingdom, France, Belgium, Tunisia, Luxembourg), a fact that reflects the global and true international nature of the workshop. We hope that these proceedings will serve as a valuable reference for researchers and developers of wireless systems and mobile applications and services. Based upon the MobiWac TPC recommendation, the following three papers have been selected as candidates for the MobiWac 2006 Best Paper Award: "Sink Mobility Protocols for Data Collection in Wireless Sensor Networks", Ioannis Chatzigiannakis (Computer Technology Institute, GR), Athanasios Kinalis, Sotiris Nikoletseas (Univ. of Patras and Computer Technology Institute, GR) "Quick Convergecast in ZigBee/IEEE 802.15.4 Tree-Based Wireless Sensor Networks", Yu-Chee Tseng, Meng-Shiuan Pan (National Chiao-Tung University, Taiwan) "Diagnosing Mobile Ad Hoc Networks: Two Distributed Comparison-Based Self-Diagnosis Protocols", Mourad Elhadef, Azzedine Boukerche, Hisham El-Kadiki (University of Ottawa, Canada) We are pleased to announce the Winner of the Best Paper selected for MobiWac 2005, in Maui, Hawaii: "On the Effectiveness of Logical Device Aggregation in Multi-radio Multi-hop Networks," Michele Rossi, (Consorzio Ferrara Ricerche (CFR), Ferrara, Italy), Leonardo Badia, Paolo Giacon, Michele Zorzi, (Dep. of Information Eng., Univ. of Padova, Italy) Putting together MobiWac 2006 was a team effort. First of all, we would like to thank the authors for having participated so numerous with their submissions, and for having contributed in this way to the growth of the workshop. We would like to express our gratitude to the technical program committee and external reviewers, who worked very hard in reviewing papers and providing suggestions for their improvements, by contributing to the quality of the program. We would also like to thank Ioannis Chatzigiannakis and Mirela Sechi Moretti Annoni Notare, Publicity Co-Chairs, for their effort in advertising the workshop. Special thanks go to Enrique Alba Torres for having hosted this workshop together with MSWiM 2006, and to the Local Organizing Committee for their work on the local arrangements. Finally, we would like to thank the ACM, our sponsor, for their continued support of these successful meetings, and the MSWiM Symposium Organizing Committee, for hosting the workshop. We hope that you will enjoy the MobiWac 2006 Technical workshop program, as well as the technical program of the MSWiM 2006 Symposium and, last but not least, your stay in Spain. Albert Y. Zomaya MobiWac 2006 General Chair University of Sydney, Australia Luciano Bononi MobiWac 2006 Program Chair University of Bologna, Italy