OK well, it’s been a long time since I’ve blogged
anything. Someone be sure and tell
@networkstatic about this. He’ll be
proud. Here goes…
I wanted to talk about the wonders of DWDM and how it works.
Let’s start by stating the meaning of the acronym. DWDM – Dense Wave Division Multiplexing. Dense is a relative term in this
context. The other type of WDM is CWDM,
which is Course Wave Division Multiplexing.
Course wave is great for smaller scale because the gear is cheap and you
can get away with “dirty” fiber. Dense
wave has higher density multiplexers.
The latest one I’ve heard of for 10gb channels give you 96 channels of
10gb. The last one I heard of for 100gb,
gives you 44 channels of 100gb.
So - what does it do?
How does it work? Why would you
use it?
What does it do? It
allows companies and service providers to leverage just one pair of fiber to
carry multiple “channels” of data. Each
channel acts like a different physical connection within the same fiber
cable. Sometimes when explaining it at a
high level, I describe it like this: “Think of each channel as a 60 mile long
patch cable.”
How does it work? To
me, this is the cool part. Inside of one
of the module of the DWDM gear is a prism.
Everyone is probably familiar with the Pink Floyd’s Dark Side of the
Moon album cover that looks like this:
So, why does this happen?
Why does the light scatter like that?
According to Joseph Von Fraunhofer, when light travels through
air, all of the colors in the spectrum travel at the same speed. However, when that same light passes through
a prism, the light slows down and changes direction. Since the light is passing through glass at
an angle and the different colors of light vibrate at different frequencies,
the different colors of light begin to travel at different speeds. This speed difference between the colors
causes them to break apart as they pass through the prism. Maybe I’m just a total geek, but I find that
very cool.
Why would you use it?
There are several use cases for this technology. Probably the most widely used, but taken for
granted, is transcontinental communication.
There are thousands of miles of fiber optic cable laying on the floor of
the world’s oceans. Check out this
website to see all of this cable and who owns it. This is one of my favorite websites: http://www.submarinecablemap.com/. DWDM technology is used at the landing points
to maximize the use of the fiber strands.
Another use case would be for companies that needs to move
large amounts of data between data centers in very short spans of time. For instance, storage replication is a common
reason for implementing DWDM. I’ve seen
cases where companies need a layer two adjacency between data centers. Using DWDM over dark fiber is a great option
over VPLS or pseudowire, depending on the needed scale and distance.
One of the more compelling cases is to replace more
expensive, slow managed services with much faster, cheaper equipment that is
far more scalable. When trying to price
large bandwidth connections between data centers, some companies will lease
wavelength services from a carrier. This
can be a good interim option. However, I
have found that you can actually buy the fiber gear and have multiple strands
of dark fiber run between your data centers more cheaply than wavelength
services.
Some companies could even build a DWDM ring to replace the
function of the Local Exchange Carrier for remote office connectivity. This particular option requires colocation of
your DWDM gear in a carrier hotel.
Taking over the LEC function provides a far more flexible, manageable
and more cost effective solution than traditional carriers can provide.
The flexibility gained by the use of DWDM is simply
unmatched. One of the sites I visit for
news on DWDM is: http://www.lightwaveonline.com/network-design/dwdm-roadm.html
I hope this gives you information you didn’t already
have. Happy Computing!
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