During the last years, the Advanced Broadband Communications Center (CCABA) of the UPC has been involved in several projects related to Internet traffic monitoring and analysis in the Spanish National Research and Education Network (RedIRIS), namely CASTBA, MEHARI [1] and MIRA [2, 3]. As a result of such an experience, a new traffic monitoring and analysis system, called SMARTxAC, has been developed at CCABA in joint work with the Supercomputing Center of Catalonia (CESCA). SMARTxAC is an always-on passive monitoring and analysis system that operates at gigabit speeds without packet loss. It also integrates a web-based graphical interface that offers numerous traffic statistics online. The main difference between SMARTxAC and other passive measurement infrastructures and systems for high-speed networks, such as those instrumented by NLANR [4] and Sprint [5], lies in that SMARTxAC has been explicitly designed for online traffic analysis, whereas in other approaches traffic analysis tasks are usually postponed to an offline stage.