This part of IEC 61281 is a generic specification for optical fibre communication subsystems (FOCSs). The subsystems are classified into families with common partial specifications. Each partial specification is supplemented with a blank detail specification, and with detail specifications applicable to a particular type or type of subsystem. The parameters defined here form the minimum set of specifiable specifications common to all optical fibre subsystems. Depending on the specific application and technology, additional parameters may be required. These additional parameters will be specified in the relevant partial specifications and/or detail specifications. Each specified parameter can be measured using one of the test procedures. Guidance on the use of these parameters for system design is given in the Design Guide.