25 Gigabit Ethernet( 25GbE) was developed for data center and backplanecabling. The IEEE 802.3by and 802.3cc standardization bodies have specified various 25GbE interfaces for monomode fiber, multimode fiber, backplane cabling and copper cable for 25GbE technology. The nomenclature of the 25GbE interfaces corresponds to the well-known Ethernet nomenclature 25GBase-xxx and characterizes in the appendix (xxx) the wavelength of the optical fiber, the coding and the wavelength division multiplexing(WDM).
As for copper cabling, the backplane cabling is done through the backplane PCB. For this application, there is the 25GbE interface 25GBase-KR and the 25GBase-KR-S variant. The bridgeable distance is 1 m. For copper-based interfaces, there is the 25GBase- CR for twinaxial cables with a length of up to 5 m, and the 25GBase-CR-S variant. Twisted pair is used with the 25GBase-T interface with four-pair balanced copper cables of category 7 and 8.
Distances from 70 m to several kilometers are supported by the fiber optic interfaces25GBase- SR (S, Short), 25GBase-LR (L, Long) and 25GBase- ER (E, Extra Long). The designations S, L and E also refer to the wavelength used. 25GBase-SR uses multimode fibers with a wavelength of 850 nm, which is indicated by the letter S. 25GBase-LR uses single- mode fibers and wavelengths between 1,295 nm and 1,325 nm, and 25GBase-ER, which also uses single-mode fibers, transmits at a long wavelength of 1,550 nm.