This book constitutes the proceedings of the 4th International Workshop on Traffic Monitoring and Analysis, TMA 2012, held in Vienna, Austria, in March 2012. The thoroughly refereed 10 full papers and 8 short papers presented in this volume were carefully reviewed and selected from 31 submissions. The contributions are organized in topical sections on traffic analysis and characterization: new results and improved measurement techniques; measurement for QoS, security and service level agreements; and tools for network measurement and experimentation.

This book collects a selection of the papers presented at the 21st International Tyrrhenian Workshop on Digital Communications, organized by CNIT and dedicated this year to the theme "Trustworthy Internet." The workshop provided a lively discussion on the challenges involved in reshaping the Internet into a trustworthy reality, articulated around the Internet by and for People, the Internet of Contents, the Internet of Services and the Internet of Things, supported by the Network Infrastructure foundation. The papers have been revised after the workshop to take account of feedbacks received by the audience. The book also includes: i) an introduction by the Editors, setting the scene and presenting evolution scenarios; ii) five papers written by the session chairmen, reputed scientists, and each dedicated to a facet of the trustworthy Internet vision; iii) a concluding paper, reporting the outcomes of a panel held at the conclusion of the workshop, written by the two keynote speakers.