HP ProCurve Tech Brief: 10-Gigabit Ethernet Cabling

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Copper is the de facto standard for transmitting data
between devices due to its low cost, easy installation,
and flexibility. It also possesses distinct shortcomings.
Copper is best when utilized in short lengths, typically
100 m or less. When employed over long distances,
electromagnetic signal characteristics hinder
performance. In addition, bundling copper cabling can
cause interference, making it difficult to employ as a
comprehensive backbone. For these reasons, copper
cabling has become the principal data-carrying
technique for communication among PCs and LANs,
but not for campus or long-distance transmission.
On the other hand, fiber cabling is typically used for
remote campus connectivity, crowded wiring closets,
long-distance communications, and environments
that need protection from interference, such as
manufacturing areas. Because it is very reliable and
less susceptible to attenuation, it is ideal for sending
data beyond 100 m. However, fiber is also more costly
than copper and its use is typically limited to those
applications that demand it.
As a result, most organizations utilize a combination of
copper and fiber cabling. As these companies
transition to 10-GbE functionality, they must have a
solid understanding of the various cabling
technologies and a sound migration strategy to provide
a cabling infrastructure that will support their network
infrastructure, both today and tomorrow.
The evolution of cabling
technologies
Just as gigabit and 10-GbE technologies have changed,
so have the cabling technologies that support them.
In fact, evolutions of cabling technologies have walked
in-step with, and been largely driven by, evolutions
to gigabit and 10-GbE standards. Both IEEE 802.3
standards and the associated cabling technologies have
assumed many forms in order to enhance a variety of
environments.
A grasp of the particular gigabit or 10-GbE standard
being employed is just as important as an
understanding of the circumstance and environment—
factoring distance of data transmission, equipment
being utilized, and budget—in order to determine
what cabling strategy best suits a particular
organization. Just as the difference between sending
data 100 m and 100 km affects the more effective
cabling strategy, so does the difference between
sending data with IEEE 802.3ae and IEEE 802.3ak
standards.
The 10-GbE standards outlined below help define and
enhance the environment in which they operate and
the cabling technologies over which they
communicate.
IEEE 802.3ae
Ratified in June 2002, the IEEE 802.3ae LAN standard
was developed to update the preexisting IEEE 802.3
standard for 10-GbE fiber transmission. With the new
standard, six new media types were defined for LAN,
metropolitan area network (MAN) and wide area
network (WAN) connectivity:
• 10GBASE-SR—uses the lowest-cost optics (850 nm) to
support 10-GbE transmission over standard
multimode fiber for distances of 33 and 82 m. The SR
standard also supports up to 300 m using the new
2000 MHz*km multimode fiber (laser optimized). SR
is the lowest-cost optics of all defined 10-GbE optics.
• 10GBASE-LR—uses higher-cost optics (1310 nm) than
SR and requires more complex alignment of the
optics to support single-mode fiber up to 10 km.
• 10GBASE-LX4—supports traditional FDDI-grade
multimode fiber for distances up to 300 m using
Coarse Wavelength Division Multiplexing (CWDM),
which lowers the transmission rate of each
wavelength to 3.125 Gbaud. The LX4 standard also
supports single-mode fiber for up to 10 km. LX4 is
more expensive than both SR and LR because it
requires four times the optical and electrical circuitry
in addition to optical multiplexers. Over time, the
quantity of components required to implement the
technology may limit its ability to fit into smaller
form factors.
• 10GBASE-ER—uses the most expensive optics
(1550 nm) to support single-mode fiber up to 30 km.
For 40 km, the fiber-optic connection must be an
engineered link.
• 10GBASE-LRM—The LRM standard was ratified in
November 2006, and supports up to 220 m over
standard multimode fiber. Using a technology called
Electronic Dispersion Compensation (EDC), 10GBASE-
LRM can provide a long-distance solution based on
multimode fiber and operates with a single
wavelength (1310 nm).
• 10GBASE-SW, 10GBASE-LW, 10GBASE-EW—defined
for use with a WAN PHY. These standards were
defined to operate at the same baud rate as OC-
192/STM-64 SONET/SDH equipment. They are the
equivalent of the SR, LR, and ER standards and
support the same fiber cabling. LX4 does not have an
equivalent WAN PHY standard.