The calibration kit CAS ISN is made for function tests and remeasurements on impedance stabilization network (ISN) for unshielded balanced pairs. Measuring parameters are common mode (CM) impedance, phase angle, voltage division factor, decoupling attenuation (isolation) and longitudinal conversion loss (LCL). Impedance stabilization networks (ISN) are defined in CISPR 22 and CISPR 16-1-2. The CISPR 16-1-2 gives additional requirements and provides examples and measurements for the networks. The ITU-T recommendations G.117 and O.9 offers the background knowledge for measurements on symmetrical telecommunication lines.