H3C Technologies H3C S12500 Series Switches - Manual (Page 9)

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reach the receiving end early or late as the transmission distance increases, which in turn causes
impulse broadening, making the signal values indistinguishable.
To meet different transmission distance requirements, choose fiber transceiver modules according to
actual networking conditions.
Central wavelength
Central wavelength represents the wave band used for optical signal transmission. At present, there are
mainly three central wavelengths for common fiber transceiver modules: 850 nm, 1310 nm, and 1550 nm,
respectively representing three wavebands.
• The 850 nm wave band is mainly used for short-reach transmission.
• The 1310 nm and 1550 nm wave bands are mainly used for middle- and long-reach transmission.
Fiber
Fiber types
Fibers are classified as multimode fibers and single-mode fibers.
• Multimode fibers
Multimode fibers (MMFs) have thicker fiber cores and can transport light in multiple modes.
However, the inter-mode dispersion is greater and worsens as the transmission distance increases.
Multimode fibers can be classified into multiple grades according to their diameters and modal
bandwidth. For more information, see
Table 2 . The modal bandwidth of a multimode fiber is
determined by the expression the modulation frequency of the maximum modulation frequency
pulse that can pass a fiber × the fiber length. The modal bandwidth is a comprehensive index
reflecting the optical characteristics of a multimode fiber.
International Telecommunication Union (ITU) defines multimode fiber types in its G series
standards. The commonly-used multimode fiber is defined in the ITU G.651 standard. The
G.651-compliant fiber transmits light at the wavelength range 800 nm to 900 nm or 1200 nm to
1350 nm.
Table 2 Multimode fiber grades
Fiber mode Fiber grade Fiber diameter (μm)
Modal bandwidth at
850 nm (MHz*km)
Multimode fiber
OM1 62.5/125 200
OM2 50/125 500
OM3 50/125 1500
Other factors that influence the transmission distance of multimode fibers include interface type,
central wavelength, and fiber grade. For more information, see
Table 3 .
Table 3 Multimode fiber specifications
Interface type
Central
wavelength (nm)
Fiber grade Transmission distance
1000BASE-SX 850
OM1 < 275 m (902.23 ft)
OM2 < 550 m (1804.46 ft)