Digital designs have not traditionally suffered by issues associated with transmission line effects. At lower frequencies the signals remain within data characterization and the system performs as designed. But as system speeds increase, the higher frequency impact on the system means that not only the digital properties, but also the analog effects within the system must be considered. These problems are likely to come to the forefront with increasing data rates for both I/O interfaces and memory interfaces, but particulalry with the high-speed transciever technology being embedded into FPGAs.
Transmission line effects can have a significant effect on the data being sent. At low speeds, the frequency response has little influence on the signal, unless the transmission medium is particularly long. However, as speed increases, high-frequency effects take over and even the shortest lines can suffer from problems such as ringing, crosstalk, reflections, and ground bounce, seriously hampering the integrity (response) of the signal. You can overcome these issues by following good design techniques and simple layout guidelines, as described in this document.