802.3z
Three distinct standards are specified under the 802.3z standard; they are referred to collectively as 1000BaseX.
The three standards are 1000BaseLX, 1000BaseSX, and 1000BaseCX. 1000BaseLX and 1000BaseSX use long wavelength laser and short wavelength laser, respectively. Both 1000BaseSX and 1000BaseLX can be supported over two types of multimode fiber62.5 and 50 micron-diameter fibers. Only long wave lasers support the use of single-mode fiber.
The 1000BaseCX standard specifies Gigabit Ethernet over STP cabling. Segment length of 1000BaseCX is extremely limited, reaching a maximum of 25 meters. 1000BaseCX is not widely implemented.