5 commonly asked questions about fiber-optic cabling

After 25 years in the industry, CommScope’s director of field application engineering Mike Cooper has heard a lot, including certain questions about fiber-optic cabling over and over again.

Whether deployed in a data center, a cellular wireless network, or a central office, fiber-optic cable is the subject of many questions commonly asked by design and installation professionals.
Whether deployed in a data center, a cellular wireless network, or a central office, fiber-optic cable is the subject of many questions commonly asked by design and installation professionals.

By Mike Cooper, RCDD, DCDC, NTS; CommScope

In my 25 years in the industry, I have seen and heard a lot of things. More than anything, I get a fair number of questions on fiber—everything from how to suspend and bend it to how it fits into European regulations. Even as director of the North American field application engineer team, many of these questions are the same no matter where I am. I’ve rounded up a few of the most-asked here. What are your questions?

1. How long of a span can I suspend self-supporting fiber?

Most self-supporting fiber-optic cables can mechanically withstand the loads of longer distances that are typically specified for each cable. However, the span lengths are often limited by the strain placed on the fiber-optic glass inside the cable and/or by the minimum clearance requirements provided by the National Electrical Safety Code (NESC).

CommScope provides span lengths in three categories: NESC vehicular access, NESC pedestrian access, and infinity within each NESC loading category: heavy, medium and light. When a self-supporting fiber cable is latched to a support strand such as a ¼-inch 6.6M EHS strand, the self-support span limitations no longer apply because the load is being placed on the strand and not the cable.

The only sure way to know the limitations is to review the specifications for the cable.

2. Can I bend fiber around a sharp corner?

In the past, we were limited to where and how we placed slack storage. We devised spools up in overhead tray to keep a large bend radius. Sometimes we’d run patches through different frames to keep the bends out and take up all the slack needed. Now that reduced bend radius (RBR) fiber is rated to a particular standard, there are panels, frames, wall boxes, etc. that can spool the slack right in the unit.

But does this mean you no longer worry about how to handle slack coils? Does bend-induced loss go away? Do you even bother testing for it? There are still fiber-optic glass bend radius standards. ITU-T G.657.A1 has a minimum bend radius of 10mm, G.657.A2/B2 at 7.5mm and G.657.B3 down to 5mm. With specified bend radii, you need to maintain clean systems with the proper RBR. There may still be bend loss, but maybe not in the same way as the past. Historically, you would trace the fiber to physically see the bend. With today’s fiber, the bend loss might indicate more of an improper seating of a connector or a routing issue in a splice tray.

RBR fiber is a great step in fiber technology that will expand to all parts of the network—even the outside plant. Keep in mind, with proper use and cable management, technicians should be able to eliminate bend loss through the entire network.

3. I have heard about 8-fiber connectivity, but use 12-fiber MPOs. Do I need to switch?

There is a saying about how “less is more,” but in this case, the opposite is true. The short answer is no. You do not need to switch. If managed well, a 12-fiber MPO infrastructure with more fibers per connector provides 50 percent more usable fibers per connector in the same footprint. This is valuable as evolving standards continue to use duplex fibers as connectivity options through at least 100 Gbits/sec.

The main reason for introduction of 8-fiber MPO connectors was to provide application support of parallel signals using 8 of the available 12 fiber positions of the industry-standard 12-fiber MPO connector. This application typically occurs in a QSFP (Quad Small Form-factor Pluggable) transceiver. Examples of this transceiver would be the 40GBase-SR4 or 100GBase-SR4, where four pairs of fiber deliver 10G or 25G each to achieve a channel of 40 Gbits/sec or 100 Gbits/sec.

There are other multifiber connector options, such as the 12-fiber MPO or the 24-fiber MPO, which continues to gain popularity in the market. Both are industry standard. The higher-fiber-count MPOs provide much more architectural flexibility and trunk efficiency compared to the 8-fiber application.

4. Will fiber be the best solution to connect cellular network radios in the future?

That is the consensus. Mobile network operators will opt for fiber as the preferred technology for backhaul and fronthaul to cellular network radios wherever possible because of the ever-increasing bandwidth requirements of today and into the future.

The density of radios for future cellular will drive the requirement for network convergence between wired and wireless traffic, increasing the requirement for fiber network solutions that focus on providing the density, accessibility and flexibility to support multiple applications needed for the future.

Another major driver is to reduce power usage and optimize space utilization at the tower. Many operators are now transitioning to C-RAN (centralized RAN) architecture—and fiber is key to the transition. With C-RAN, baseband units (BBUs) are moved away from the bottom of the tower and into central offices or BBU pooling locations, which can be located many kilometers away.

At the central office, the BBUs from multiple cell sites are pooled and connected to the remote radio head via fronthaul connectivity (to carry data from the cell sites to the BBU pool) and backhaul (to carry data from the BBUs back to the core network).

C-RAN offers an effective way to increase the capacity, reliability and flexibility of the network while lowering operational costs. It is also a necessary step along the path to cloud-RAN, where the BBU functionality will become “virtualized”—allowing for greater elasticity and scalability for future network requirements.

5. How does one confirm compliance of fiber-optic cables to new European CPR regulations for in-building applications?

Introduced in 1989 by European regulators, the Construction Product Directive (CPD), later the Construction Product Regulation (CPR), was designed to ensure materials and equipment that make up buildings such as offices, schools, and shops are safe from fire hazards and other risks.

With further classification published in 2016 on how products such as communications cables react to fire, a deadline for the mandatory CE marking of cables was set for July 1, 2017. The European Commission mandates construction materials like fiber optics have a common technical language like CPR 305/2011, for example.

All manufacturing facilities serving the European market will need to have been audited and approved by Notified Bodies, and the building industry will be required to work only with vendors that have carried out extensive testing with these Notified Bodies, and can provide the proper Declarations of Performance for their cabling products, organized in Euroclasses A to F.

Every product will be required to carry the CE label appropriate to the applicable Euroclassification. The type of testing is determined by the type of verification system being used by the Notified Body. Euroclass Cca and B2ca use the most stringent verification “System 1+,” requiring continuous audits and of the production facility and product testing. System 3 includes Euroclass Dca and Eca, which are lower safety classes.

Approximately 80 percent of the Notified Bodies are accredited for System 1+ and can assign Euroclass Cca and above. It’s important for organizations to ensure they are using the appropriate Notified Body, which can be found on the NANDO website of the European Commission.

Mike Cooper, RCDD, DCDC, NTS is director of field application engineering with CommScope.

More in Wireless/5G