The MODE CONDITIONING (MC) cables are applied in systems, in which the modern active devices of the Gigabit Ethernet technology are connected by means of the existing multimode cabling. They make it possible to increase the transmission distance of the 1000BASE-LX technology to 550 m for OM1 cables. MC cables are duplex cables, at the end of which - on the transmission side - there is a section of single-mode cable. Next, a single-mode cable is connected with a multimode cable in a special manner, thus yielding an enhanced quality of signal propagation in the multimode cable. The MC technology consists in the optimum introduction of the signal from a single-mode fibre-optic cable to a multi-mode one, which is achieved by the displacement of cores. A single-mode signal is not introduced in the axis of the multimode fibre-optic core, because in such a situation there are many parallel signals, which interact and cause the so-called Differential Mode Delay (DMD parameter), thus limiting the transmission distance.