December 12, 2000, 1:38 PM — Enterprise networks face a condition called fiber exhaust when the demand
for backbone fiber exceeds the availability of installed fiber strands.
The most obvious and expensive solution to fiber exhaust is to install more fiber.
However, the costs associated with running and terminating the new fiber, and the
restrictions involved with rights of way, open tray or duct space, and access to buried
fiber often make this a less-than-attractive option.
An alternative is to say no to those who want to place new applications on the fiber
infrastructure. However, saying no is neither popular nor politically correct.
Another option is to remove the less critical applications from your fiber network
to make room for the newer ones. However, telling users that they can no longer use
their fiber connections won't win you any popularity contests either.
DWDM to the rescue
Fortunately, a relatively new technology called Dense Wave Division Multiplexing (DWDM)
can boost the capacity of a single fiber pair by as much as 32 times.
Prior to DWDM, only one light beam at a time traveled down each single- or
multi-mode fiber strand. Since network data travels in two directions, it took a pair
of strands to make a single network connection -- one strand for transmission, the
other for reception.
DWDM is able to increase the total bandwidth of the fiber because instead of using a
single-color laser beam (typically a white beam), it sends multiple-color beams, called
lambdas or channels, down the same fiber pair. Multiple frequencies
of light offer more bandwidth in a fiber strand in much the same way that different
radio frequencies offer many FM stations on a single radio band.
Each lambda can carry its own independent signal, providing the same overall
bandwidth per channel (approximately 2.4 Gbps with most of today's fiber) that a
single-color laser does. Thus, if you run DWDM with eight lambdas, you increase the
capacity of a fiber pair from 2.4 Gbps to 19.2 Gbps. This creates virtual dark
fiber, which enterprise networks can use to run multiple higher-layer technologies
such as ATM and Gigabit Ethernet simultaneously over the same physical fiber
DWDM can be configured in a simple point-to-point configuration, a hub architecture
in which all connections run to a single DWDM device, a chain, or a ring. In a ring
configuration, DWDM can bring fault tolerance to point-to-point networks such as ATM
and Gigabit Ethernet.