 premises and telephone exchanges (at telecom operators' premises) which are typically in the range up to 5-6 km (of course, there are also shorter lines in the local loop, depending on the concrete loca- tion of the user). ADSL was the main broadband fixed access technology in the 2000s because it reused existing copper lines (i.e. twisted pairs) deployed for telephony in the twentieth century. The standards ADSL2 [4] and later ADSL2+ [5] provided over 10 Mbit/s and 20 Mbit/s in the downlink direction, respectively (Table 4.1), and hence have prolonged the ADSL lifetime until the 2010s. 4.1.1.1 ADSL (Asymmetric DSL) Figure 4.1 shows a typical deployment of the ADSL network architecture. The access consists of DSLAM (digital subscriber line access multiplexer) nodes, to which are con- nected digital local loops. Typically several local loops end into a single DSLAM, which further aggregates the IP traffic from users, and vice versa in the opposite direction. The Table 4.1 Main ADSL broadband standards and bitrates. Downstream Upstream bitrate (max) bitrate (max) ADSL name (Mbit/s) (Mbit/s) Standard name ANSI T1.413-1998 ADSL (G.DMT) ITU G.992.1 Splitterless ADSL (G.Lite) ITU G.992.2 ADSL2 ITU G.992.3 Splitterless ADSL2 ITU G.992.4 ADSL2+ ITU G.992.5 4 QoS for Fixed Ultra-Broadband IP networks IP traffic Circuit-switched voice Customer router AAA servers network DSLAM IP backbone Aggregation network IP network Customer network router AAA - Authentication, authorization and accounting ADSL - Asymmetric digital subscriber line BRAS - Broadband remote access server DSLAM - Digital subscriber line access multiplexer PSTN - Public switched telephone network Figure 4.1 ADSL network architecture. main gateway node between the ADSL access network and the IP core network of the telecom operator is a broadband remote access server (BRAS), a router node which car- ries out AAA functions (by communication with a centralized AAA server, such as the RADIUS server). The BRAS performs traffic aggregation from the access network (