High frequency attenuation will cause the switching time of a given bit
to vary depending on the previous bits. You can model this very simply
by running a pulse stream through an RC low pass filter. For example,
if the rise time of the system is reduced to be equal to a bit time,
then the shape of a bit and its pulse width will be reduced if it has
been proceeded long string of bits of the opposite polarity.
While cables don't exhibit a single pole response, it is a useful
approximation. A couple hours with a pulse generator, scope and some
resistors and capacitors will give a good feeling for the problem
without expensive high frequency equipment.
Most communications textbooks discuss this sort of thing in excruciating
IBM Rochester, MN