 and partly by channel bonding. Eurodocsis is essentially a redistribution of the uplink/downlink budget to support the 8-MHz digital TV channel bandwidths and data rates needed to meet European DVB-C broadcast requirements. Table 2.6 shows DVB-C modulation options and data rates. Present standardisation efforts are being directed towards producing a new iteration of DVB-C known as DVB-C2. Hybrid Fibre Coaxial Systems In a hybrid fibre coaxial system, the optically modulated signal at a fibre node is downconverted to an RF modulated signal that begins at 50 MHz but extends to 550 to 1000 MHz. The reverse path is either between 5 and 42 MHz (ATSC in the US) or 5 to 65 MHz (DVB C in the rest of the world). The downstream is either carrying 6-MHz ATSC channels or 8-MHz DVB C channels. Table 2.5 Three generations of DOCSIS cable specification DOCSIS DOWNSTREAM UPSTREAM DOCSIS 1.0 38 Mbit/s 9 Mbit/s DOCSIS 2 38 Mbit/s 27 Mbit/s EURODOCSIS 2/DVB C 51 Mbits 9 Mbit/s DOCSIS 3.0 160 Mbit/s 120 Mbit/s 18 IPV6 is addressed in a later chapter. Physical Layer Connectivity Table 2.6 Example modulation options and data rates for an 8-MHz digital TV cable channel Modulation 16 QAM 32 QAM 64 QAM 128 QAM 256 QAM Data rate Mbit/s 25.64 32.05 38.47 44.88 51.29 2.9 The DVB-S Satellite Alternative HFC networks are directly competitive with satellite networks. Satellites are power-budget limited. For this reason, DVB S satellites use QPSK or 8 PSK modulation. These modulation schemes have less amplitude modulation than QAM schemes and therefore support more power-efficient RF power amplifiers. Present standardisation efforts are being directed towards producing a new iteration of DVB-S, known as DVB-S2 based on using 16 and 32 PSK modulation combined with adaptive variable source coding (AVC). Table 2.7 shows the data rates needed for present SDTV and HDTV transmission and the possible data rates achievable using AVC coding. High-definition TV occupies over four times the bandwidth of a standard definition transmission. Compression sch