|No matter who you are or what industry you are in, if you are
responsible for a network, the odds are that you are looking for ways to expand
your bandwidth capabilities not reduce them.
There are many options to consider in your quest and of course as a
savvy professional, you have already learned that there is definitely a right
way and a wrong way to go about it. One
thing is for certain; if you have already installed fiber optic cable in your
network, bandwidth expansion is much easier to accomplish.
For years now, Wide Area Network (WAN) owners, also referred to as carriers or service providers, have enjoyed the benefits of a highly advanced
technology called DWDM or Dense Wave Division Multiplexing. The basic concept of DWDM relies on the fact
that a single fiber has nearly infinite capacity and this can be exploited by
using different wavelengths for each fiber channel being transmitted.
The problem with DWDM technology is that it is cost prohibited for
anyone except carriers who typically have several hundred-thousand
to millions of customers paying the bill for the equipment.
Today however, with the advancements in passive restricted channel multiplexers,
as well as the advent of multiple SFP (Small Form-factor Pluggable) wavelengths
available at relatively low costs, just about any network owner with a quality
built fiber optic network can play the game. The emphasis is on the words "quality
built” fiber optic network, because as you stack
multiple wavelengths on the same fiber, the combined signal becomes
increasingly sensitive proportionately. The more wavelengths you add, the more
sensitive the transmission becomes to network imperfections. This is why we rarely try to multiplex on
multimode fiber, as there are just too many inherent imperfections and
restrictions in the fiber itself.
However, if you had originally selected singlemode fiber for your
network, all you may need is a bit of a connection or splice upgrade in order
to run the simplest form of multiplexing WDM (or) the next level CWDM (Course
Wave Division Multiplexing) in your network.
Some forms of WDM are already experienced through
active dual wavelength SFPs, but it is important to note that this is a more
expensive form of multiplexing than the passive multiplexer. With passive multiplexing, it is relatively
easy to stack 4 to 8 independently produced SFP wavelengths onto a single fiber
or fiber pair, creating a more cost-effective CDWM circuit.
When you are ready to increase the capacity of your network by 4 to
8 fold, you will have a few up front tasks to accomplish. First, you will need to select the CWDM
modules for deployment (let’s say 4 channel) and in doing so your base
wavelengths will be identified. This is
because the CWDM module will be optimized for a specific range of wavelengths
in order to ensure proper channel separation is maintained in accordance with
ITU (International Telecom Union) mandates. Your next task will be to re-certify your network to the more specific
Standards requirement for accommodating multiple wavelength applications. This is often done by a network consultant or
Independent Verification Consultant that has the appropriate instruments with
programmable acceptance criteria and other test parameters such as PMD
(Polarization Mode Dispersion) and CD (Chromatic Dispersion) measurements.
Once the front end work has been accomplished, the actual process
of converting to an acceptable multiplexed circuit is relatively easy. Where normally, four independent circuits
would launch from independent SFPs and connect to four separate fiber pairs,
the new scheme would be that the four independent circuits would plug into the individual
channel inputs of the CWDM module with a single fiber or fiber pair output
taking up the slot of the four fibers previously used.
And there you have it, increasing
the capacity of your existing bandwidth pipeline without pulling any new fiber.
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