Last Updated: December 17, 2020
One of the questions I often get from fiber optic cable manufacturers is: “Which specifications do I have to qualify to?” Additionally, I often hear: “Why is it that this particular specification is not good enough? Why can’t one spec fit all?”
Unfortunately, a one-size-fits-all approach doesn’t work in today’s optical cable world.
Why were so many different specifications created?
To understand why the various specs were created, we have to go back to the basics. The oldest specifications out there were written in the early days of fiber optics. This was a time when fiber was considered delicate, with a little dose of “black magic.” When those early specs were created, say in the 1980s, the number of people worldwide who could actually handle and install cable was in the hundreds. In today’s world, many fiber optic cables are, if you will, commodity products that are handled by tens of thousands of skilled technicians around the world. Many specifications continue to evolve, yet some specs have become set in stone. And, over time, new specifications have been added.
One reason so many different specs have been created is that each application may seem to have special needs. Initially, we were using fiber optic cable for long-haul telecommunications. Now we’ve expanded into the data communications world. We have Fiber To The Office (FTTO) along with cable TV and the Internet – Fiber To The Home (FTTH). These applications were talked about only in a very “future” way in the 1980’s and even in the 1990’s. Each application has its own set of needs, has a new set of slightly different requirements, and has resulted in a new specification – one that is particularly related to the application.
Plus, we have industry and government agencies that say: “We have special needs, and we’re going to require that you meet those needs.” The first major government specifications were, of course, related to military applications. Military requirements for tactical cable are very different – very non-standard from other requirements. It made sense that military applications required manufacturers to develop robust, flexible, secure, and “handle-able” cables that might be buried, because you don’t want someone to find, tap, or cut those cables.
The second major industry and government development was when cables went into new applications. As soon as the old REA (Rural Electrification Administration) became the Rural Development Utilities Programs, the methods changed. They suddenly announced, “We need cables that can be installed on existing networks – on poles or buried out in the middle of the prairie or in very thinly populated areas.” So their specifications called for different requirements: easier handle-ability, easier workability, and behavior that was close to the copper cables these folks had been using. Next, cables started moving into areas like oil and gas fields to maintain the instrumentation. As each new application came along, organizations added new requirements that were unique to their industry. Over the years, a lot of specifications came out for different markets and different applications.
Cables then and now: Why cables of 10 or 20 years ago needed different specs
Two things have happened in the past decade or so. The first is that cable designs have evolved. Fiber optic cables that were manufactured 20 years ago – even 10 years ago – were much less generic in nature. The advent of the bend-insensitive optical fiber (both single mode and multimode) has made cables much more user-friendly in the last decade. Therefore, the fact is that manufacturers could get sloppier in the design of their cables, so the specifications began to call for different types of tests. Today, each specification has been updated by the relative issuing bodies: Telcordia, RDUP or the US military DOD, and even end users such as Verizon, which created its own TPRs (Technical Purchase Requirements) for its products.
Second, the knowledge base of the people who install these cables has grown and evolved as well as the methods and tools. As an example, many years ago it was common to see copper cable pulling devices that had very small radii pulling fiber optic cables. At the time, those cables could not withstand that tight end radius.
The installation methodology was a problem at the time. No one really knew how to specify the cables’ bend radius (other then 10 or 20 times the cable diameter) or realized that if you wrapped it around a number of cables under tension, as you would in various pulling devices, it could cause a problem. Well, the pulling devices have also evolved significantly over the years for fiber optic cable.
Today, installation methods are much different than they were back then. So the specifications in some areas could be “loosened up,” as is seen by the fact that, for many years, we have made rugged, reinforced stranded core cables with loose tubes and central GRP strength members with outer yarns or fiberglass as well as armor and jackets to pull it through conduits. Over time, we’ve thinned this out significantly to a central tube design that’s much less expensive, bringing down the price of cable. This also means the termination is easier.
Cable designs are evolving. The cable installation methods and tools are evolving. There is a significant change in how we install cables today. It’s much simpler and much more forgiving. The training and required skills are significantly different than they were 10 or 20 years ago. In addition, access to the cables with new tools and new cable designs is easier, so termination has become a simpler matter.
BUT all those specifications still exist due to the different classes of use for cable, whether it’s a Telcordia spec for telecommunications, or it’s an indoor/outdoor cable, or the cable is installed in an oil field, which may have significant chemical-resistance requirements.
A global disagreement on safety requirements results in different specifications.
Safety requirements have evolved differently for the US and Europe and, as a result, specifications have proliferated. For example, when it comes to fire and flammability, in many parts of the world fiber optic cables are required to have a low-smoke, zero-halogen makeup. In other words, halogenated gas is not generated when the cable burns. In the US, we took a different approach with our riser and plenum products – we look at flame spread and smoke generation. Therefore, you have different requirements in the US and Europe regarding how materials are used as well as how cables installed in buildings or in crafts would be evaluated. Various Asian countries follow either the US or European models.
Another example concerns aerial tension requirements. Worldwide, the decisions about aerial tension requirements for self-supporting cables or drop cables are based upon practices in a given country or a given culture. In certain developing countries, these cables must be able to support a ladder leaning against the cable, along with the weight of a person (typically 120 or 150 kilograms). In the US, you would be expected to use a bucket truck or some other method to access these cables.
Other cables with aerial tension requirements are used in different applications such as breakaway cables for long-haul self-support. When we talk about “long-haul self-support cables,” we’re referring to cables that would be on transmission towers or cables that might have a steel messenger wire embedded in a figure-eight or shot-gun configuration. These cables are very strong, typically 3,000 to 5,000 pounds (or greater) breaking strength.
One big concern is whether the cable is strung across a road. Here’s an incident that actually happened in Texas: A fiber optic cable sagged after a storm, causing it to hang low over traffic. A semi-truck snagged the cable on its trailer, and the cable peeled off the entire top of the trailer. Also, the cable was pulled off poles for about ½ kilometer. This incident shows there are good reasons to develop specific breakaway values that are very different than, for example, telecommunications cable requirements, which typically have a 2700-Newton or 600-pound break strength.
Let’s look at another example of why different specifications would have different aerial tension requirements: Ice and wind conditions. Even during a major storm, the amount of wind and weather your cable would need to withstand in, say, southern California is minimal compared to the Northeast. A New England ice storm can deliver sub-zero temperatures with sustained winds of 40 to 60 miles an hour – along with an inch of ice on the cable. Clearly, these two different environments demand a different set of requirements.
Evolving optical transmission requirements and optical hardware have impacted specifications.
We used to have a specification that said: “You’re going to work at these particular wavelengths: 850 and 1300 nanometers for multimode and 1310 and 1550 nanometers for single mode.” With the advent of both coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM), we have to look at broader applications. We’re actually measuring cables differently, depending on where they’re going. It would be very rare, for example, on a short-haul cable in a data center – that might require a kilometer or two of cable – to have a large amount of DWDM applications. But this would be very common on a 20- or 50-kilometer run of telecommunications cable. Changing optical transmission technology requirements has had a major impact on specifications over the last few years.
Another reason why there are many specifications: Cable is going where no cable has gone before!
To paraphrase Gene Roddenberry (creator of Star Trek), we are going where no one has gone before. In the fiber optic world, we are putting cables in places we never thought we would. We’re embedding cable in concrete with sensors that monitor the strength and stress of buildings and bridges. We are embedding cable in aircraft wings to measure stress on the aircraft. We are bringing cable into your living room. We are laying it underground for the oil and gas industry and, of course, under the ocean. We are using cable in subways to monitor stress on tunnels. We have done a lot of things with cable and put it in places no one ever expected it to go. Of course, these extremely different applications and environments require very different specifications.
So the real question is: “Which market will your cable serve?”
Remember that our initial question in this discussion was this: “Which specs should you qualify to?” Some people think the answer is to cover all the generic specifications applicable to telecommunications and data communications. However, any cable that is completely compliant to all those specifications would end up looking something like this old saying: “a camel is a horse designed by committee.” In other words, your results simply wouldn’t meet the mark. Thanks to increasingly diverse applications, I think fiber optic cables will continue to be more and more specialized. For this reason, I think specifications will continue to proliferate, since material needs are different, optical performance needs are different, and the physical environments are different. That’s why the question really comes down to this: “Which market will your cable serve?” Your chosen market and application will drive the specifications you qualify your fiber optic cable to.