In the past 20 years,
bandwidth demands have increased more
than 1000 fold. As data has converged
with voice, 2 meg Powerpoint files have
converged with electronic postcards
of dancing reindeer to clog the desktop
connections and to fill campus backbones.
Fortunately, Ethernet technology has
been up for the challenge. When the
first Ethernet products shipped in 1986,
(at a blazing 10 Mbit/sec), few ever
dreamed that the technology would be
deployed over 85% of desktops in less
than 15 years. By 1995, a Fast Ethernet
(100 Mbit/sec) standard was ratified.
Now Gigabit Ethernet (1000 Mbit/sec)
is almost ubiquitous in campus backbones
and is moving to the desktop. This explosion
has made even faster speeds necessary,
and 10
Gigabit Ethernet (10,000) is rapidly
making its way into LAN and carrier
networks around the world.
This ever expanding array of speeds
and technology has made the job of the
system designer harder than ever. Gone
are the days when multimode always meant
62.5 micron, and single mode was never
needed until cable lengths stretched
over 2 km. The Gigabit Ethernet standard
introduced VCSELs (Vertical Cavity Surface
Emitting Laser) and mode conditioning
patch cords making many fiber backbones
obsolete.
Prior to Gigabit Ethernet (GbE), multimode
fiber was designed for operation with
LED transmitters. The LED worked very
well for 10 and 100 Mbit/s Ethernet.
It provided a coherent light source
that completely flooded all of the pathways
(modes) in a multimode fiber. Multimode
fiber was designed to work with LEDs,
and LED bandwidth was measured (Over
Filled Launch bandwidth or OFL). Gigabit
Ethernet proved to be more demanding
however, as a single transmitter is
blinking fast enough to send 1,000,000,000
bits of information each second. In
order to accomplish this type of speed,
two GbE standards were introduced, and
both of them rely on lasers instead
of LED’s.
IEEE 802.3z is the governing standard
for Gigabit Ethernet. The standard introduced
a short range (SX) and a long range
(LX) option for GbE transport. The SX
option operates in the 850 nm window,
and is designed for multimode fiber
only. Instead of an LED transmitter,
SX technology relies on an 850 nm VCSEL.
The LX option is designed for longer
distances over single mode fiber. It
can also be used over multimode fiber,
usually requiring a mode conditioning
patch cord to effectively launch the
single mode laser into the multimode
core.
While before, multimode always worked
up to 2 km, now the system designer
has a menu of options to choose from.
Depending on wavelength (SX or LX),
fiber core size and effective modal
bandwidth (laser bandwidth), the capacity
of multimode fibers ranges from 220
meters to 1 km. Fiber Connections offers
a range of options, summarized in the
chart below.
Gigabit Ethernet-Multimode
62.5/125
| |
62.5 µm
FDDI grade 850/1300 nm |
62.5/125
µm 850/1300 nm |
62.5 µm
InfiniCor® 850/1300 nm |
62.5 µm
InfiniCor® CL 850/1300 nm |
Gigabit Ethernet Distance Guarantee
(meters)
|
220/550* |
275/550* |
300/550* |
500/1000 |
OFL BW (MHz • km)
|
160/500 |
200/500 |
200/500 |
200/500 |
Effective Modal Bandwidth (MHz
• km)
|
— |
— |
220/— |
385/— |
Maximum Attenuation (dB/km)
|
3.75/1.5 |
3.5/1.0 |
3.5/1.0 |
3.5/1.0 |
| *requires mode conditioning patch
cord at 1300 nm |
|
Gigabit Ethernet-Multimode
50/125 and Single Mode
| |
50 µm
InfiniCor® 600 850/1300 nm |
50 µm
InfiniCor®SX 850/1300 nm |
50 µm
InfiniCor® SX+ 850/1300 nm |
SInglemode
1310/1550 nm |
Gigabit Ethernet Distance Guarantee
(m)
|
600/600 |
750/600 |
1000/600 |
5 km |
OFL BW (MHz • km)
|
500/500 |
1000/500 |
1500/500 |
— |
Effective Modal Bandwidth (MHz
• km)
|
510/— |
1000/— |
2000/— |
— |
| Maximum Attenuation (dB/km) |
3.5/1.5 |
3.5/1.5 |
3.5/1.5 |
0.5/0.4 |
All of these fiber types are available
in variety of indoor and outdoor cables.
|
