hown in Figure 13.31. 13.12 FIXED SYSTEMS Figure 13.32 provides an overview of fixed access systems. 13.12.1 COPPER-BASED SYSTEM FRAGMENTATION The drop part of the fixed accesses is dominated by copper-based solutions. Many solu- tions have a name that includes DSL (digital subscriber line). Very efficient modulation schemes enable bandwidths far beyond ISDN 2B + D. There are also fixed radio solutions (LMDS, fixed cellular systems), coaxial cable systems, often called cable modem systems or cable TV (CATV) systems, and finally fibre Access Network Fibre Ethernet ADSL, VDSL, SHDSL, Access node Access transport Multi-service packet backbone network ISDN/ Modem FR, SDH Figure 13.32 Fixed systems overview (NMDS: narrowband multi-service delivery system) systems to enterprises and to basements, curbs and other points very close to residential subscribers. A possibly upcoming solution is a power line. 13.12.2 ADSL + G.LITE Asymmetric digital subscriber line (ADSL) provides broadband access on the existing PSTN pair cable to the home. At the same time you may continue using your ordinary telephone. Separation is achieved by means of a 'splitter'. The data is sent on unused frequencies above 3400 Hz. This interface is called 'asymmetric' since the downstream flow is much bigger than the upstream flow. Often you download more than you upload, SO this is a preferred division for most users. For peer-to-peer communication and small office/home office activities with a balanced traffic in-out a symmetric DSL solution may be better. The actual bandwidth of ADSL depends on technique but also on operator policy. addition to the original standard there is a standard called G.Lite with lower bit rate but cheaper, since it is a splitterless design. G.lite is also known as universal ADSL, and referred to as G.992.2 by the ITU. Downstream transmission rates from the carrier to the subscriber premises range between 0.5 Mbit/s and 8.0 Mbit/s depending on type, whereas upstream transmission rates are nor- mally up to 1 Mbit/s. The pos