Chris – First, remember that link segment does not equal cable. A link segment is the transmission path between the two MDIs, which may contain connectors, filters,
and other passive devices.
While it might be tempting to add a qualitative statement as below, adding such a paragraph is technically meaningless. It provides nothing that can be evaluated.
For example – is that only specifying a zero-frequency null? To what depth? After what frequency should the exponential be held? Under a constraint like that, you could have a band-stop filter starting at 10 MHz (say, if you wanted a mid-span Power injector).
That is why the lower frequency bound is important – it provides technical clarity on the performance that a PHY implementer can expect of the link segment. I think that German’s point is quite valid, and have seen examples where assuming that the link segment
would be well behaved (rather than specifying it) causes problems for PHYs, such as those German describes.