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Before you Dig: The DWDM Difference Whitepaper

The large amount of CapEx involved in building out new fiber is enough to make any service provider pause before starting up a cable plow. Digging up the ground also takes a great deal of time and expends a lot of resources. Therefore, most service providers put off deploying new fiber as long as they possibly can. Nevertheless, they know that they must meet sustained and exponentially increasing demand for bandwidth somehow.

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For example, Bell Labs has forecasted a 560% increase in metro network traffic by 20171. Service providers with metro and long-haul fiber networks are under unprecedented pressure to prepare their networks to meet customer needs that ultimately could exceed current forecasts. The impact of variables such as the Internet of Things (IoT), 4K Ultra HD, and other applications that will need consume massive bandwidth remains unknown. The unforeseen spike in demand for video applications and cellular backhaul that took mobile providers by surprise practically overnight is just as likely to manifest in some as yet unknown form in the next few years.


Fortunately, service providers do have a way to optimize their fiber networks without digging. Dense wave division multiplexing (DWDM) is a mature, proven and cost-effective technology that breathes new life into existing fiber architectures. Service providers that have not yet considered deploying DWDM are beginning to seriously think about giving it a try or further exploring this time- and money- saving fiber expansion solution.

What is DWDM
First Introduced in the mid-1990s (Figure 1), DWDM systems employ multiplexers/demultiplexers that use lasers to place many closely spaced wavelengths onto a single fiber and take them off when they reach their destination. If conversions or regeneration of signals is required, transponders are added to the architecture. Much has been learned about optical networking over the years. As a result, today’s 100 Gigabit (G) systems can support up to 96 wavelengths and 9.6 Terabits of bandwidth. Currently, 200G systems are making their debut in service providers’ networks while vendors put the finishing touches on 400G systems, which are waiting in the wings.

Many people think of DWDM as a technology that is used to increase the capacity of ultra-long haul networks that span across the nation or under the sea. However, the technology can also be used to revitalize fiber used in long-haul and regional networks.

In addition to providing significantly more capacity using fiber that would otherwise be considered “exhausted,” DWDM systems are attractive to service providers because they are easy to install and maintain. They also can be installed without taking existing services off line when augmenting ring architectures. Capacity is added by lighting up a new wavelength. Most transport equipment vendors support DWDM small form factor pluggable (SFP) optics in their systems, which help to keep incremental costs for each new channel low. DWDM systems are able to transmit wavelengths across longer distances than time division multiplexing (TDM) systems, which are more prone to chromatic- and polarization-mode dispersion.3

DWDM systems employ standardized optics that utilize the same frequencies. Therefore, service providers are not locked into using equipment provided by a single vendor. System pricing reflects the competitive market for equipment and the improved cost effectiveness and performance compared to TDM-based equipment.

The return on investment (ROI) is quick. For example, a service provider that has an add-drop multiplexer on a two-fiber SONET OC-12 ring can install a new 10G Ethernet ring using eight-channel mux/demux units and transponders. Doing so converts the OC-12 wavelengths to DWDM channels and provides an additional seven wavelengths to that circuit. The capital expense to the service provider is the cost of the DWDM equipment plus a relatively minimal investment in labor for installation, configuration and turn-up. Even when physical construction is a viable alternative to DWDM, it has the potential to create distractions, necessitate the use of political capital or stir-up goodwill risks associated with rights-of-way and potential unnecessary use of new or restricted construction corridors. The consistent advantages of using DWDM include predictable turn-up timeframes and improved certainty of cost and effort.



In addition to not having to dig, a service provider that installs DWDM in support of existing fibers does not have to strand any legacy SONET equipment in its network. A carrier that is running out of fibers anywhere in its network as it evolves from SONET to an Ethernet backbone, or when adding additional Ethernet circuits, can install DWDM today to solve pressing issues and gain valuable experience that will come in handy when inevitable increases in demand for bandwidth occur in the not-so-distant future.

Improving Your Network With DWDM

Why make the move?
In addition to providing significantly more capacity When it comes to making the decision on whether or not to add DWDM technology to a network, mindset is critical. Service providers with plenty of fiber at their disposal today may feel like they are good-to-go for years to come. As mentioned above, this may not be the case. Gaining some experience with DWDM deployment in portions of their networks that make sense today will improve service providers’ responses to bandwidth requests and provide them with an advantage over competitors that are not investing in the same type of strategy. Measurements and statistics concerning increased variables associated with the addition of various technologies to carriers’ networks have gone up and down over the past 20 years, but demand for bandwidth has never wavered.

“The average monthly consumption [of data] was 9,665 Petabytes (PB) in 2010 and will climb to 116,539 PB by 2015, according to an IDC report.’Despite enormous growth projected in IDC’s forecast, it is difficult to overestimate this phenomenon. Fixed and mobile operators will have to deal with a new reality that will tax network resources to the limit —and perhaps past the limit,’ said Matt Davis, an analyst with IDC4.”

“An estimated one-third of the world’s population is online now, a proportion that is sure to grow. More users, more devices that connect to networks, and more data-heavy services to ride over the pipes are causing a “bandwidth explosion,” [John] D’Ambrosia [head of the IEEE bandwidth assessment group and chairman of the Ethernet Alliance industry group] said. The data reviewed by his IEEE committees over the past few years indicates that bandwidth demand is growing faster than our capacity to deliver it5.”

Certainly, service providers’ experience tells them that making investments in new equipment tends to offer up at least as many challenges as it does benefits. DWDM is an exception to that rule as it is virtually plug-and-play. Its ease of deployment is a compelling reason for service providers to review reasons to deploy it sooner rather than later.

In fact, service providers that install DWDM today will be well positioned to install it in other areas of their network going forward. The need for more fiber capacity is already here for service providers that are in a position to provide cellular carriers with much- needed fiber facilities for mobile backhaul. The same applies to service providers with customers in the financial industry as an increasing number of banks and other financial institutions order gigabit Ethernet (GigE) connections.

In an effort to serve customers with multiple locations outside of their footprints, or provide high-bandwidth connections to data centers, many service providers are leasing increasing amounts of fiber. By installing multiple-wavelength DWDM systems on leased fiber, they can exponentially increase the amount of bandwidth it yields. They also are minimizing the number of fibers they need to lease and continue to grow their businesses without worrying about increased bandwidth requirements.

In addition to deploying DWDM systems, service providers can build their own solutions by installing DWDM optics in their existing electronics. For example, it is possible to equip two routers terminating each end of a circuit with SFP optics tuned to DWDM wavelengths. By doing this, a direct connection to the mux/demux units can be done, increasing the available bandwidth between both locations.

Last but not least, migrating to DWDM systems enables service providers to modernize older networks. With DWDM, service providers can layer leading-edge data services on top of existing investments in legacy SONET infrastructures.

In summary, making the move to DWDM is a wise decision because it is a mature, cost-effective optical technology that works well with existing fiber. The experience of installing and using DWDM gives service providers the edge should the opportunity arise to gain new customers or expand services to existing customers on routes in which their fiber is filled to capacity today, or in the future.

Cost-Benefit Analysis

Incumbent local exchange carriers (ILECs), competitive local exchange carriers (CLECs), Internet service providers (ISPs) middle mile transport providers, and utilities are all looking for ways to maximize the optical fiber they have at their disposal. Some have a great deal of experience with it, while others do not. It is not uncommon to find service providers using multiple strands of fiber to carry circuits in the same direction. This inefficiency can be remedied very easily with DWDM technology.

In addition, service providers with limited availability of fiber due to leases or bottlenecks in their networks can use DWDM to gain instant relief from capacity issues that have been percolating for some time. The systems also place them in a position to meet any sudden demands for bandwidth from customers or across the regions they serve.

The expense of installing fiber vs. the lower cost of installing DWDM is clear. A small system that will multiplex two dark fibers into eight available channels, including conversion of existing 1GigE or SONET OC-48 circuits into a DWDM wavelength, costs less than $40,000 with spares. This is equivalent in price to installing approximately two to three miles of fiber cable.


Smart Choice
Service providers that decide to install DWDM in their networks quickly realize its many benefits. DWDM is affordable, easy to deploy and it provides immediate capacity on otherwise exhausted fiber. The ability to quickly add up to 96 wavelengths onto a single fiber pair enables service providers to save on both CapEx and OpEx. It also enables them to easily meet expected or unexpected demand for more capacity anywhere they need it without delay.

Installing DWDM systems using on-net fiber, inserting it on leased lines, or placing DWDM optics on routers enables service providers to add capacity as it is needed with very little effort while simultaneously improving their bottom lines. Service providers that put DWDM to work in their networks today are better prepared to meet the increasing bandwidth needs of their customers and any unforeseen demand spurred by new technologies or market variables. Finally, with DWDM, digging becomes the choice of last resort for service providers that want to expand their existing fiber optic networks.


1. Lightwave – “Bell Labs forecasts 560% increase in metro network traffic by 2017,” traffic-by-2017.html

2. Dublin Institute of Technology, School of Electronic and Communications Engineering, Applied Optoelectronics Centre, 802529,d.cWc


4. Tom’s Hardware – “Broadband Bandwidth Demand to Jump 10X by 2015,”,15013.html

5. Ars Technica – “Bandwidth explosion: As Internet use soars, can bottlenecks be averted?,” be-averted/)


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