DSL transfers data over specific frequencies. Certain frequencies will resonate better than others over certain lines. Here is an image of a line test conducted for a VDSL2 customer: http://wut.nz/images/spm/1027296.jpg. The redder the graph, the faster (up to the maximum VDSL2 speed) the connection is.
The vertical line is when the connection spontaneously resynced, and a new speed was attained based on the new conditions of the line.
For this particular customer, you can see that tones 410-460 show no transfer at all. This causes a reduction in speed, since those frequencies couldn't be used.
The vertical line is when the connection spontaneously resynced, and a new speed was attained based on the new conditions of the line.
For this particular customer, you can see that tones 410-460 show no transfer at all. This causes a reduction in speed, since those frequencies couldn't be used.