ITU-T K.44 is the basic recommendation of the ITU-T K series on the protection of telecommunication equipment, and it defines the resistibility tests themselves. Where the other recommendations in the series state the levels that a particular class of equipment must withstand, this document specifies how the tests are performed: the generators and their waveforms, the coupling arrangements, the test configurations for each port and for combinations of ports, the number of applications and the interval between them, and the conditions under which the equipment is operated while the test is applied. It covers tests at power frequency, representing the situation in which a power conductor comes into contact with a telecommunication line, and impulse tests that represent lightning, and it explains how the outcome of a test is judged, including the acceptable degradation of performance and the requirement that a failure must not create a hazard. The document is used as the reference for the whole family of equipment resistibility recommendations.