The requirement of connecting the transmitter of one side to the receiver on the other side and vice versa makes it necessary to always have an "odd number of crossovers" between two devices, with an MDI-X port containing an internal crossover. Thus, connecting MDI to MDI-X requires a straight-through cable (one crossover in total). Connecting MDI to MDI (no crossover) or MDI-X to MDI-X (two crossovers) requires a(nother) crossover in the cable to get an odd number. When using more complicated setups through multiple patch panels in structured cabling, the connection can use multiple patch and building cable segments. It is a good idea to have all necessary crossovers on one side, i.e. either on the central hub/switch or on each secondary hub/switch.