They consider the noise to be couples to the line code. In the case of aerial local loop wiring, the VDSL signal on the cable will generate an electric field capable of interfering with ham radio bands. BT Labs has carried out some measurements in high frequency bands generated by cables that carry VDSL signals. Other measurements included the total path loss from the launch point of the VDSL signal in the the UTP and to the ham radio receiver. VDSL systems that are based on TDD may require power control measures to prevent this kind of interference.
Asymmetric service is that in which the upstream and downstream channels have different bit rates.
It has been agreed that asymmetric and symmetric systems are possible. Furthermore, mixing of the two systems in VDSL implementations seems possible. Symmetric VDSL is planned for short distances and asymmetric operation is planned for long range. On the other hand, an advantage of the asymmetric system is the fact that it simplifies the electronic equipment required an the home side of the loop. The European TM6 committee has commented that they would like to see VDSL transceivers that can be configured both for symmetric and asymmetric operation.