It is reported in the literature that electrical-field enhancements can appear in irregular deformed wave-guides. Using Maxwell's equations it is rather difficult to find analytical solutions for these arrangements. On the other hand, it is long been known that wave-guides can be approximated by systems of transmission line equations. In the paper we present this framework for studying cylindrical wave-guides from a geometric point of view and explain how random variables for the description of roughness of the wave-guide surface can be introduce. Finally, we add some comments about a simple example.