Describes two methods for determining and measuring the modal bandwidth of multi-mode optical fibres (see IEC 60793-2-10, IEC 60793-2-30 and IEC 60793-2-40).The baseband frequency response is directly measured in the frequency domain by determining the fibre response to a sinusoidally modulated light source, it can also be measured by observing the broadening of a narrow pulse of light. Method A - Optical time domain measurement method (pulse distortion). Method 2 - Frequency domain measurement method. Each method can be performed using one of two launches: an overfilled launch (OFL) condition or a restricted mode launch (RML) condition.