HP ProCurve Tech Brief: 100BASE-FX Ethernet

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Introduction
New technologies generate great excitement, but sometimes older technologies continue to
serve important needs. An example of such a technology is 100BASE-FX.
Although 100BASE-FX was developed in the mid-1990s, it is still in use today, 10 years later,
when we also have Gigabit and 10-Gigabit available. Why? One reason is that 100-FX has the
longest range over multimode fiberoptic cable of any Ethernet technology. While 100-FX can
reach two kilometers using any quality of multimode fiber, the Gigabit maximum range is 550
meters, and 10-Gigabit maximum range is 300 meters on only the highest-quality multimode
fiber.
Fiberoptic cabling provides several benefits over copper cabling: noise immunity, no
electromagnetic emissions, and it is difficult to tap or eavesdrop, in addition to supporting long
distances. There are two types of fiberoptic cabling: multimode and singlemode. Multimode
fiberoptic cabling is much less expensive than singlemode, although singlemode fiber provides
greater distances. The 100BASE-FX standard specifies multimode fiber as the transmission
medium.
Because 100-FX operates over multimode fiber and reaches distances up to two kilometers,
there continues to be widespread use of 100-FX as a cost-effective way to extend Ethernet
networks. ProCurve Networking by HP supports 100-FX in our new switches, so that our
customers can continue to get the most from their old fiber and take advantage of whatever
fiber type, distance and speed best serves their needs. By creatively connecting the past with
the future, ProCurve offers both investment protection and the flexibility that comes with choice
— all of which adds long-term value to ProCurve solutions.
Quick history
Two goals that networking standards bodies struggle to achieve are speed and distance.
Ethernet keeps evolving to speeds that are 10 times faster than the previous generation. And
fiberoptic cabling allows networks to reach distances far greater than the standard 100 meters
supported by copper cabling.
The success of 10-Megabit Ethernet led to the creation of 100-Megabit "Fast" Ethernet in the
early 1990s. FDDI was created to provide 100-Megabit connectivity over multimode fiberoptic
cabling, with a maximum distance of two kilometers between stations. So when the IEEE
developed the 100BASE-FX specification for 100-Megabit Ethernet over fiberoptic cabling, one
goal was to allow a maximum distance of two kilometers over multimode fiber, to match FDDI
capabilities.
Fiberoptic cable installers were careful to adhere to the FDDI and 100-FX distance
specifications, and companies were careful to limit their multimode fiber links to two kilometers
or less. This allowed network expansion at 100-Megabit speeds.
Today, many companies are installing singlemode fiberoptic cabling primarily to gain higher
speed network links, because singlemode fiber preserves signal integrity and allows extremely
long distances and high speeds. But singlemode fiber is more expensive to install than
multimode, and the networking components that send signals over singlemode fiber are more
expensive than the components that send signals over multimode fiber.
Benefits of 100BASE-FX
After a decade of existence, there are still good reasons to use 100-FX. There are many
applications where higher speed is not needed and where there is existing multimode fiber in
place. When 100 Megabits/sec is adequate, there are several benefits of 100-FX:
• can extend the network to greater distances than copper cabling can support
• noise immunity (fiber is immune to external interference)
• security (fiber is difficult, though not impossible, to tap)
• electrical immunity (there are no grounding issues with fiber)
Factories can be difficult environments for computer networks due to many sources of external
interference that can affect the signal on copper cabling. For factories, fiber-based networks are
often the only option.