I. Introduction
The dominance of the Internet Protocol (IP) within data networks seems today to be clearer than ever before. The expectations in the late 1980s/early 1990s that asynchronous transfer mode (ATM) would be the future network protocol have not materialized. Internet applications constitute the overwhelming majority of data applications running over wired data networks; at the same time the penetration of IP in wireless networks is increasing, embracing different access technologies.