This invention aims to ensure that a VDSL line gains or remain at the same speed when vectored. For a given line in a vectored group or joining a vectored group, an estimate is made of its channel capacity without vectoring enabled, and an estimate is made of its channel capacity with vectoring enabled. If the estimated channel capacity of the line with vectoring enabled is lower than without vectoring enabled, then the vectoring coefficients representing the impact of the other lines into that line are zeroed. In effect, vectoring is turned off for that line, but remains active for other lines including the effect of that line into the other lines. The invention is particularly useful for lines with metallic issues or other faults, which could lose speed when vectored due as a result of inaccuracies in the crosstalk channel matrix used in the vectoring process.
