How many DWDM channels do access networks need?

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Fiber optics and DWDM technology are moving to the edges of networks. Meeting the ambitious performance goals of 5G architectures requires more fiber links than ever before between small cell sites and when replacing legacy TDM transmission with higher capacity DWDM links (Figure 1). In the case of fixed access, new architectures such as Remote PHY free up ports in cable operators’ headends that can be used to deliver more bandwidth to more customers.

A Deloitte report summarizes the reasons for the need to extend the reach and capacity of optical access networks: “Extending optical fiber deeper into communities is a critical economic driver, fostering competition, increasing connectivity for rural and underserved areas and supporting densification for wireless”.

To achieve today’s objectives, operators of fixed and mobile access networks in dense areas need to make the most of their fiber capacity, so they seek to apply DWDM. The technology has become cheaper than ever due to the availability of low cost filters and SFP transceivers with greater photonic integration. Additionally, self-tuning modules have made installation and maintenance of transceivers easier and more affordable.

Despite the benefits of DWDM, its price often makes operators wonder if the upgrade is worth it. Fortunately, they can now choose between narrowband and fullband tunable modules that offer different amounts of wavelength channels. These choices provide an optimal fit for budget and network requirements.

Applications for full-band tunable

Let’s examine what happens when fixed access networks need to be migrated to a distributed access architecture like Remote PHY. A single optical node serving 500 customers is divided into 10 nodes of 50 customers. By dividing an optical node into 10, a provider can grow from 8 to 80 nodes. Each of these nodes requires the cable company to assign a new DWDM channel, so the provider must increasingly use C-band optical spectrum to accommodate all of these DWDM channels. Network upgrades like this are a typical example of a situation where tunable modules that cover the entire C-band and have narrow grid spacing are practical (Figure 2).

Additionally, a single full-band DWDM transceiver reference can handle all the wavelengths needed for the network. In the past, network operators used fixed wavelength DWDM modules that could only be used in specific ports. For example, an SFP+ module with a C16 wavelength can only work with the C16 wavelength port of a DWDM multiplexer. However, tunable SFP+ modules can connect to any port on a DWDM multiplexer. This advantage means that technicians no longer have to navigate a confusing sea of ​​fixed modules with specific wavelengths; one adjustable module and one part number will do.

Overall, full band tunable transceivers will suit applications that require a large number of wavelength channels to maximize fiber infrastructure capacity. Metro transport or Data Center Interconnects (DCI) are good examples of applications with such requirements.

Applications for narrowband tunable

The transition to 5G will require a significant restructuring of the architecture of mobile networks. 5G networks will use higher frequency bands, which will require deploying more cell sites and antennas to cover the same geographic areas as 4G. Additionally, existing antennas need to be upgraded to denser antenna arrays. These requirements will put more strain on existing fiber infrastructure, and mobile network operators are expected to deliver on their 5G promises with relatively little expansion of their fiber footprint.

DWDM will be vital for mobile network operators as the capacity needed in cell towers skyrockets with new 5G architectures. Tunable SFP+ DWDM transceivers can handle this increased optical traffic, but operators often consider traditional full-band tunable modules to be expensive for this application. Mobile frontends don’t need all 40-80 channels of a full-band transceiver. It’s like having a cable subscription where you only watch 10 out of 80 TV channels.

Therefore, an alternative approach is to develop narrowband DWDM transceivers with only eight channels. They offer an alternative that allows for more affordable and moderate capacity expansion. Advances in photonic integration and packaging now enable modules that can help scale mobile access networks cost-effectively. With these modules, operators can reduce inventory compared to gray transceivers while avoiding the cost of a full band transceiver.

Overall, narrowband tunable transceivers will be suitable for applications in areas of the network that require relatively low density aggregation.

Synergy with auto-tuning algorithms

The sheer number of channels in a tunable module (up to 100 in the case of high-end full-range modules) can quickly become overwhelming for technicians in the field. There will be more files to review, more programming for tuning equipment, more trucks to load with tuning equipment and more checks to be done in the field. These tasks can take a few hours for a single node. If there are hundreds of nodes to install or repair, the man-hours required will quickly run into the thousands and the associated costs into the hundreds of thousands. Self-tuning modules play an important role in overcoming these problems and making network deployment and maintenance easier and more affordable.

Autotuning allows technicians to treat DWDM tunable modules the same way they treat gray transceivers. There is no need for additional training for technicians to install the adjustable module. There is no need to program tuning equipment or obsessively check wavelength records and tables to avoid field deployment errors. Technicians simply follow typical cleaning and handling procedures, plug in the transceiver, and the device will automatically scan and find the correct wavelength when plugged in. This feature can save providers thousands of man-hours in installing and maintaining their network and reduce the likelihood of human error, effectively reducing CAPEX and OPEX.

Take away food

Full-band self-tuning modules will allow providers to deploy extensive network upgrades faster than ever. However, in use cases such as mobile access networks where operators do not need a wide range of DWDM channels, they can opt for narrowband transceivers which are more affordable than their full band alternatives. By combining full-band and narrow-band modules with self-tuning algorithms, operators can expand their networks in an affordable and accessible way.

JOOST VERBERK is Director of Product Management at EFFECT Photonics. He made his career in product management, working for ENGIE before joining EFFECT Photonics, where he leads the cross-functional product management team.

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