Leaving No Trace
We may be nearing an era where copper is coming to an end. With Verizon leading the way in the U.S., fiber-to-the-home (FTTH) is quickly becoming a preferred technology for delivering telephone, Internet, and video services to the home in both greenfield and brownfield applications. The lifespan of existing coaxial and copper plant may be extended by DOCSIS, FTTN, and VDSL2, but as bandwidth demands keep increasing, it’s inevitable that fiber directly to the subscriber will become the standard for deploying new infrastructure in the outside plant.
Further fiber requirements are being fuelled by the success of bandwidth-intensive wireless devices such as BlackBerry® and iPhone. These, of course, are driving cellular network upgrades. Distributed antenna systems (DAS) are being deployed in cities across the nation to service the increasing bandwidth demand; DAS networks are interconnected using fiber.
We are in the midst of an enormous telecom infrastructure overhaul. The copper network that served us over the last century will be replaced by the fiber network that will connect us to the 21st Century.
How can a new national fiber network be deployed cost-effectively and with minimal impact?
In many urban areas, existing leasable duct is either at capacity or doesn’t reach the desired end point. Cities are increasingly reluctant to allow carriers to excavate their streets, and the restoration fees involved can often make a fiber build cost prohibitive.
In existing brownfield suburban areas where there are no aerial facilities and limited or no green space to bore or trench, costs and community disruption are a huge factor.
New methods for fiber deployment that reduce cost, increase speed of installation, and minimize community impact need to be explored.
Digging Into Micro Trenching
Over the last several years, micro trenching has evolved as a cost-effective and non disruptive method for deploying fiber that will play a significant role in building the network of the future.
The concept is simple. Rather than dig a 3-foot-deep trench or dig multiple pits for directional boring, micro trenching uses a narrow and shallow trench (typically 1/2 inch wide by 5 to 8 inches deep) to bury the fiber directly in the roadway, sidewalk, or grass boulevard.
In concrete or asphalt, the saw cut is typically reinstated with a cold patch asphalt restoration product enabling a total installation time that is fast compared to traditional methods, and, once restored, leaves a footprint that is barely visible. In grassy areas the native soil is replaced and, within a few weeks, it’s as if the micro trench was never there.
To the seasoned OSP engineer, the thought of deploying fiber in anything but a conduit buried at least 36 inches underground may seem as crazy as climbing up a utility pole in a thunderstorm. However, the conduits used for micro trenching have evolved to minimize the risk of damage, and their shallow deployment means that they are quick and simple to repair should damage occur.
The reality is, with proper documentation and care, micro-trenched networks are as safe and resilient as any other buried utility. A micro-trenched installation may be worked around just like a traditional conduit.
Another key benefit of a micro-trenched network arises when extensive construction activity is underway, such as a road or sidewalk replacement, whereby the live network can be lifted, moved, and re-installed out of harm’s way.
The beauty of micro trenching is that it can be installed with small crews using light construction equipment in a very non disruptive manner, with a five person crew installing and fully restoring up to 2,000 feet per day. The narrow trench is restored as the network is being built, resulting in an extremely low impact to the community. A city block can easily be completed in a day with minimal traffic disruption.
Micro trenching has evolved to meet the growing applications for fiber. Whether it’s fiber-to-the-home, wireless backhaul or traffic and security cameras, there are a number of ways to micro-trench fiber. Three of these methods include: direct buried, air blown, and vertical inlaid fiber.
Method A. Direct Buried
A direct buried cable is typically used for static point-to-point cable runs on private property where there are no plans for future branching of the cable. Because it is directly buried, there is no way of pulling the fiber post installation, so branching is not an option. Once it's in, it's in. Therefore, it's important to use direct fiber for the right applications. For a short run across a parking lot or in a sidewalk for a camera system, direct buried micro trench fiber is economical and quick to deploy. Direct buried cables are not usually encased in conduit and are somewhat more susceptible to damage.
Method B. Air Blown
It's no coincidence that air blown fiber is big in Europe, as it is a technique developed by British Telecom in 1980. There are different types of conduit used for air blown fiber, so this method is suitable for almost any application. For micro trenching applications using a small profile conduit in a narrow and shallow saw cut, the number of fibers that can be blown is limited. The current known capacity for micro trenched air blown fiber is 216 strands.
Once the conduit is buried in the micro trench, an air compressor is connected to the blowing head and blow tube. Rather than having fiber on large spools, the micro fibers are stored in compact blowing trays and are propelled through the tubes by the air passing over the cable in the blow tube. The air does not stress or damage the cable, and fiber can be blown for a mile or more without having to splice. With the entire conduit system in place, fiber can be deployed as needed, resulting in incremental capital outlay. Fiber can be blown into empty channels at any time, and new fiber can be blown in to replace damaged cable.
Method C. Vertical Inlaid Fiber
The vertical inlaid fiber (VIF) system enables long cable runs without splicing and uses a rugged 2-piece vertical deflecting conduit (VDC) that is zippered together using the specially designed "zipper" tool with the fiber inside. VDC is then placed vertically in the narrow saw cut with the cables stacked vertically. The design maximizes the strength of the conduit; when installed it can withstand 2,000 lbs of pressure per linear inch.
The VIF system can accommodate high fiber counts (up to 648) and the cable can be pulled, blown, or rodded through the conduit once it is installed, allowing for easy branching and repair.
A 5-channel VDC is used for FTTH path creation, with individual channels designated for backbone fibers that feed terminals. Pull string or blow tubes may be placed in the remaining empty channels which terminate at hand holes on the subscribers' property line. A standard home drop cable can then be pulled or blown through the empty VDC channels when the customer requests service.
VDC may also be extracted from the saw cut after it is installed, and branches can be easily made by pulling back slack and installing a new hand hole. This is ideal for adding laterals off the core network to expand the system to additional buildings, which is typical in urban installations.
It's All About Cost Control
In many cases, the cost of micro trenching is less than half the cost of traditional trenching or boring. The most advantageous situations for using a micro trench solution are urban or suburban areas having curb and gutter with little or no soft infrastructure in which to bore or trench. Significant cost reductions are realized by not having to restore bore pits or trenches in the road or sidewalk.
The cost of micro trenching in different infrastructures is very consistent, making it simple to budget builds accurately. Its route flexibility also enables fiber networks to access hard to reach places on both private and public property.
Micro trenching has been embraced globally with installations from Australia to Saudi Arabia, across North America, and throughout Europe. With networks being deployed in all climates -- from frigid Winnipeg, Manitoba, Canada, to the blistering heat of Riyadh, Saudi Arabia -- micro trenching has proven to be as robust as traditional installations.
Micro trenching is being used world wide as an effective alternative to traditional trenching or boring. With its low cost and minimal impact on the community, it's easy to understand why. With the ever increasing need to place more fiber in more places, faster and more economically, innovation in how we deploy fiber will enable us to build the network of the 21st Century.
About the Author
Gary Stahlbrand is Director of Product Sales, TeraSpan. He has more than 25 years experience in telecom. For more information, please visit www.teraspan.com or email him at firstname.lastname@example.org.
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