Defines the requirements for equipment to measure error performance at bit rates between 0.050 and 168 kbit/s Keywords - digital error detector; - digital pattern generator; - error performance measurement; - measurement; - tester. PREAMBLE The requirements for the characteristics of error measuring equipment which are described below must be adhered to in order to ensure compatibility between equipment produced by different manufacturers. While requirements are given for the equipment, the realization of the equipment configuration is not covered and should be given careful consideration by the designer and user. In particular, it is not required that all features listed below shall be provided in one piece of equipment. Administrations may select those functions which correspond best to their applications. When selecting functions, administrations may also consider other Recommendations dealing with error measuring equipment, e. g. Recommendations O.151 [17] and O.152 [18].