How many DWDM channels do access networks need?

Optical fiber and DWDM technology are moving to the edges of networks. Achieving the ambitious performance goals of 5G architectures requires more optical fiber links than ever 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 like Remote PHY are freeing up ports in cable operator headends that can be used to serve more bandwidth to more customers.

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

To achieve current goals, operators in fixed and mobile access networks in dense areas need to make the most of their fiber capacity, so they are looking 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. Furthermore, self-tuning modules have made the installation and maintenance of transceivers easier and more affordable.

Despite the advantages of DWDM, its price often causes operators to second-guess whether the upgrade is worth it. Fortunately, now they can choose between narrow- and full-band tunable modules that offer different amounts of wavelength channels. These choices provide an optimal fit for budget and network requirements.

Applications for a full-band tunable

Let’s look at 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 split into 10 nodes of 50 customers. By splitting one optical node into 10, a provider can expand from 8 to 80 nodes. Each of these nodes requires the cable provider to assign a new DWDM channel, so the provider needs to use more and more of the optical C-Band spectrum to fit all these DWDM channels. Network upgrades like this one are a typical example of a situation when tunable modules that cover the full C-Band and have a narrow grid spacing come in handy (Figure 2).

Furthermore, a single full-band DWDM transceiver part number can handle all the necessary wavelengths 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 could only work with the C16 wavelength port of a DWDM multiplexer. However, tunable SFP+ modules can connect to any port of a DWDM multiplexer. This advantage means technicians no longer have to navigate a confusing sea of fixed modules with specific wavelengths; a single tunable module and part number will do the job.

Overall, full-band tunable transceivers will fit applications that need a large number of wavelength channels to maximize the capacity of fiber infrastructure. Metro transport or data center interconnects (DCIs) are good examples of applications with such requirements.

Applications for a narrow-band tunable

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

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

Therefore, an alternative approach is to develop narrow-band DWDM transceivers with just eight channels. They offer an alternative that enables a more affordable and moderate capacity expansion. Photonic integration and packaging advances now enable modules that can help scale mobile access networks cost-effectively. With these modules, operators can reduce inventory compared to grey transceivers while avoiding the cost of a full-band transceiver.

Overall, narrow-band tunable transceivers will fit applications in areas of the network that need relatively low-density aggregation.

Synergy with self-tuning algorithms

The enormous number of channels in a tunable module (up to 100 in the case of top-of-the-line full-band modules) can quickly become overwhelming for technicians in the field. There will be more records to examine, more programming for tuning equipment, more trucks to load with tuning equipment, and more verifications to do in the field. These tasks can take a couple of hours just for a single node. If there are hundreds of nodes to install or repair, the required hours of labor will quickly rack up into the thousands and the associated costs into hundreds of thousands. Self-tuning modules play a significant role in overcoming these issues and making network deployment and maintenance more straightforward and more affordable.

Self-tuning enables technicians to treat DWDM tunable modules the same way they treat grey transceivers. There is no need for additional training for technicians to install the tunable module. There is no need to program tuning equipment or obsessively check the wavelength records and tables to avoid deployment errors on the field. Technicians only need to follow the typical cleaning and handling procedures, plug in the transceiver, and the device will automatically scan and find the correct wavelength once plugged. This feature can save providers thousands of person-hours in their network installation and maintenance and reduce the probability of human errors, effectively reducing capital and operational expenditures.

Takeaways

Full-band self-tuning modules will enable providers to deploy extensive network upgrades more quickly than ever. However, in use cases such as mobile access networks where operators don’t need a wide array of DWDM channels, they can opt for narrow-band transceivers that 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 has made his career in product management, working for ENGIE before joining EFFECT Photonics, where he leads the cross-functional product management team.