The presence of series resistance, or loss, in a transmission line, can lead to further effects, as shown in this slide. On the left, the input pulse is shown, and on the right, the output pulse is shown.
It can be seen that the output pulse does not reach full voltage; this is due to attenuation by the series resistance.
The rising and falling edges of the output pulse have been split into two parts - an initial fast-rising part, followed by a slowly rising part. The slowly varying part is caused by an effect called dispersion, also due to the series resistance, and it resembles the exponential decay seen in RC type circuits.
Both attenuation and dispersion can have serious performance implications in digital circuits.