The patch cord is required to comply with IEEE standards. The IEEE found that link distances could not be met with certain types of fiber-optic cable due to a problem in the center of some fiber-optic cable cores. The solution is to launch light from the laser at a precise offset from the center, which is accomplished by using the patch cord. At the output of the patch cord, the LX/LH GBIC is compliant with the IEEE 802.3z standard for 1000Base-LX.

Less than 328 feet (100 meters). When illuminating short lengths of MMF with an LX/LH GBIC, the mode-conditioning patch cord reduces the amount of optical power coupled into the MMF. Excessive power can saturate the LX/LH receiver causing an elevated bit error rate (BER) greater than 984 feet (300 meters). When illuminating long lengths of MMF with an LX/LH GBIC, the mode-conditioning patch cord offsets the laser light to reduce the possibility of differential mode delay.