still designed around centralized, processor- based architectures and were optimized for single-service-Internet access. Attempts to add advanced features such as filtering or QoS still led to performance degradation. Around year 2004 xDSL reached a critical mass deployment and several fiber-based architectures started to be proposed mainly in Asia and in the United States. Telecommunication Networks As a response to this trend, BRAS further evolved generating third generation machines. Centralized hardware gave way to distributed architecture that allowed service providers to deliver the capacity and throughput required to support advanced broadband service delivery. At this stage the BRAS functionality has also begun to be integrated into service edge routers SO to provide, through a single machine, a rich set of functionalities, for example, ATM and Ethernet aggregation Session termination and adaptation of ATM, PVC, PPP signals to the backbone MPLS/IP network Authentication, authorization, accounting Comprehensive IP routing (with the relevant protocols like BGP, open shortest path first [OSPF], RIP) IP address management-DHCP server, proxy services Integrated layer 2 switching, both on the client side using, for example, ATM or Ethernet, and on the backbone side using carrier Ethernet or MPLS Policy management and dynamic per session QoS IP multicast routing (with the relevant protocols like PIM, MBGP, IGMP) Security via firewall and intrusion detection Moreover, such complex machines started to implement reliability methods typical of core machines like 1:N interface redundancy, processor hot standby protection, and switch fabric redundancy. Besides the trend we have described up to now, pushing BRAS toward an architecture and a capacity typical to small core routers, also an alternative trend has been recently pushed by a few BRAS vendors: the move of the BRAS toward the access, up to collocat- ing it or, in some cases, to integrating it with the digital subscriber line access multiplexer (DSLAM) or the GP