Extended to 12 MHz VDSL 1 138 kHz to 5.2 to 12 to to 5.2 to 12 3.75 MHz VDSL2 25 kHz to 138 kHz to 8.5 MHz to 21.567 MHz 21.5 MHz to 138 kHz 3.75 MHz 30 MHz to 5.2 to 8.5 There will also be interference between upstream and downstream bandwidth that needs to be accommodated with guard bands although in theory the subcarriers should be orthogonal to each other and therefore should not interfere with each other. This, however, depends on the length of the loop. A connection from a home or business to a fibre node a few hundred metres away will behave differently to a medium or longer loop http://www.eetimes.com/design/communications-design/4009317/DMT-Solves-UTP-Challenges-in-VDSL- Designs/. Physical Layer Connectivity Table 2.11 Headline data rates and capacity/distance ratios Headline data rates Capacity/distance through 24 AWG Standard Upstream Downstream (0.511 mm) twisted pair 2B +D 2 by 64 kbps +16 K data Compatible with voice local loop ADSL1 1.8 Mbps 12 Mbps 1.544 Mbps at 18 000 feet 2.048 Mbps at 16 000 feet 8.448 Mbps at 9000 feet ADSL2 3.5 Mbps 12 Mbps ADSL2+ 3.3 Mbps 24 Mbps VDSL1 2.3 Mbps 51.4 Mbps 12.96 Mbps at 4500 feet 25.82 Mbps at 3000 feet 51.84 Mbps at 1000 feet VDSL 2 100 Mbps 100 Mbps As VDSL 1 though shorter distances for higher data rates application of three or four kilo feet (1-1.2 km). The longer loop will require additional echo cancellation and time-domain equalisation and the higher frequencies in the loop will be more highly attenuated. This is shown in Table 2.11. So there are two fundamental performance considerations. How does the individual point- to-point link behave and what does it do to other user's cosharing the same medium. Take for example a live bundle with a pair count of 25 twisted pairs. Once the first DSL circuit is added the amount of crosstalk will drastically increase and increase further with each additional DSL circuit. There may also be T12 and E1 signals on the line. The spectral density of these services may make them incompatible with DSL circuits. This become