This Recommendation specifies resistibility requirements and test procedures for telecommunication equipment which is installed in or on a customer premises building. Overvoltages or overcurrents covered by this Recommendation include surges due to lightning on or near the line plant, short-term induction from adjacent a.c. power lines or railway systems, earth potential rise due to power faults, direct contacts between telecommunication lines and power lines and electrostatic discharges. The sources for overvoltages in internal lines are mainly inductive coupling caused by lightning currents being conducted in nearby lightning strokes or lightning currents being conducted in nearby conductors. Major changes compared with the 2003 version of this Recommendation include: o removing the power induction test requirement for antenna ports where the installation is within the scope of K.71 o more clearly defined when the internal and external port classification applies to antenna ports