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Chapter 2Overview of current CATV network pThe support of digital signals requires the use of the appropriate modulation technique.The most widely used digital modulations for HFC networks are QAM, QPSK andVestigial Side Band (VSB).A modern CATV network for analogue video and digital services is presented inFigure 2.3. The truck cables from traditional CATV networks are replaced with highreliable,low-attenuation fibre links. This implies that a large number of the analogueamplifiers along the tree trunk are no longer needed. Hence, the reliability of the systemincreases and the quality of the signal improves, since there exist fewer activecomponents between the headend and the subscribers [12].In addition, one-way (line extender) amplifiers from traditional CATV networks needalso to be replaced by two-way amplifiers to allow upstream transmission fromsubscribers to the headend. Controllers at the headend, (referred as Cable ModemTerminations Systems -CMTS or Interactive Network Adaptor –INA) and cablemodemsneed to be installed at the headend and customer premises, respectively.Broadcast TVModern CATV NetworkFibre (Trunk)Domain< 100 milesFeeder/Distribution Cable< 1 miletaphome dropPSTNHeadendfibre trunkONUdistributioncoax cableISPInternetCATVONUtwo-wayRouterATMswitchCMTS/IAamplifiersplitterCustumer Premise EquipmetLAServerFile ServerVideo ServerresidentialhomeSet-TopBoxCable ModemFigure 2.3 – Modern CATV network with HFC architecture.2-6