Information Technology Reference
In-Depth Information
Originally, most of the gigabit switches and routers on the market still used the
traditional fiber connections. Fiber is still much more flexible in terms of the dis-
tances covered and its ease of use. Almost any multimode fiber link will support
Gigabit Ethernet at more than double the copper distance. However, for proper
operation at gigabit, enhanced Cat 5e or better cable and connectors must be
installed to the very highest standards of workmanship to be usable, and even then,
the distance is limited to only 100 m.
We should mention that a lesser-known copper standard, 1000BaseCX, exists
that uses twinax over a distance of 25 m. This standard is not often seen, but exists
to allow the short-range interconnection of two Gigabit Ethernet devices without
the need for expensive laser optics.
Fiber-Optic Standards for Gigabit Ethernet
Three fiber-optic standards are available for Gigabit Ethernet. The two primary
standards use a range of fiber modes and transceiver wavelengths and are intended
to support link distances from 220 m to 5000 m. A third standard is in develop-
ment, and equipment manufacturers are already offering this option. All require
laser optics, because of the higher bandwidth requirements for gigabit data rates.
Each fiber standard is intended to support an increasing link distance.
1000BaseSX, LX, SLX, ELX, ZX.
Table 12.1 shows the three fiber-optic stan-
dards, along with the types of optical fiber and the specified operating distance. The
TABLE 12.1
Gigabit Ethernet Fiber-Optic Link Parameters
IEEE 802.3z Wavelength,* Core/cladding Bandwidth, Range,
fiber mode nm diameter, µm Mode
†
MHz/km m
1000BaseSX 850 50/100 MMF 400-500 500-550
1000BaseSX 850 62.5/125 MMF 160-200 220-275
1000BaseLX 1300 50/100 MMF 400-500 550
1000BaseLX 1300 62.5/125 MMF 500 550
1000BaseLX 1300 10 SMF N/A 5000
1000BaseSLX
‡
1550 10 SMF N/A 10,000
1000Base ELX/ZX 1550 10 SMF N/A 70,000
*IEEE 802.3z specifies a range of values, such as 770-860 nm for 1000BaseSX; however, the accepted nominal
wavelength is shown. It should be noted that the shorter wavelength actually represents a higher light frequency
and is associated with a greater attenuation.
†MMF is multimode fiber; SMF is single-mode fiber. See Chapter 5 for details.
‡Standards for 1000BaseSLX are under review and may change in the future.
