Out With the Old Fiber: Deciding the right time to upgrade

Communications networks are always evolving to handle more data. Indoors, local area network (LAN) speeds increase regularly for wired and wireless. New architectures, such as passive optical LANs, offer logistical and financial advantages. Outdoors, networks are getting faster to connect data centers and facilitate the expansion of wireless networks with new architectures, such as small cells, distributed antenna systems (DAS) and 5G. Passive optical networks for fiber to the home (FTTH) often require new fiber networks.

Cabling upgrades to support newer and faster networks have been common for decades.

For LANs, unshielded twisted-pair (UTP) cables have gone through a half-dozen upgrades to keep up with LAN speeds. It seemed like a new UTP cable grade was coming out on a schedule similar to Moore’s law—the speed of computers doubling every 18 months. UTP copper ran out of steam when it became unfeasible to create an acceptable copper cable network for LAN speeds over 10 gigabits/second (10G.) What saved UTP cable from extinction was Wi-Fi running on power over ethernet and using the copper wires to power wireless access points in offices.

Over the same time, only two multimode optical fibers were needed for LANs. Again, 10G proved a barrier due to speed limitations of the fiber and laser transmitters. Data centers quickly became too fast for multimode fiber except when used in parallel networks, such as a link consisting of 10 pairs of fiber running 10 Gbps to equal 100 Gbps, a cumbersome solution. Data centers preferred using a pair of single-mode fibers with wavelength-division multiplexing to get the same speeds with many fewer fibers. Since single-mode fiber has practically unlimited bandwidth, it has the ability to upgrade speeds without installing new fiber.

In the outside plant (OSP), multimode fiber was only used experimentally for the first few years on a few trial networks. OSP fiber networks took off in the mid-1980s when single-mode fiber became feasible to manufacture in volume, and installation processes were perfected. That same single-mode fiber, mostly known today by its international standard nomenclature, G.652, is still the world’s most popular fiber 35 years later. And single-mode fiber represents more than 95% of all fiber installed today.

Fiber has always had such high performance that it is able to accommodate network speed upgrades more easily than copper wire, which means fiber requires fewer cabling infrastructure upgrades over time. More recently, the fast-growing volume of fiber optic links, particularly those used in FTTH and data centers, have changed the economics of fiber optics.

In any fast-growing market, higher volume means lower prices, which is a result of technical development, economies of scale and the competition between all the companies fighting for a share. That has been happening in the high-volume part of the fiber optic market. That part is the single-mode market—fiber, cable, installation and transceivers.

The high volume of single-mode components used in FTTH—where hundreds of millions of users are connected worldwide, and data centers may have 100,000 to 1 million links—has significantly affected data link pricing. Single-mode links are now at cost parity with multimode.

Single-mode fiber has always been substantially cheaper to manufacture than multimode fiber, giving single-mode cabling a cost advantage. However, Single-mode transceivers, which require more expensive laser sources for transmitters used to cost 5 to 10 times as much as multimode. The high volume of transceivers used in data centers and FTTH have driven the cost down so single-mode and multimode transceivers are now close to equal in cost. The link cost advantage certainly goes to single-mode if you consider future upgrades.

Single-mode fiber also used to be more difficult to install than multimode, mainly where termination was involved. But the fusion splice-on connector, developed to speed single-mode termination in FTTH and data centers where one might need 100,000 terminations or more, has made single-mode termination a quick, simple and inexpensive project.

In the past, many contractors were not trained or equipped to do single-mode installation. But the large number of premises projects using single-mode for DAS, passive optical LANs, OSP metropolitan networks and FTTH have changed that. Most contractors are now equipped with fusion splicers and other specialized tools and have trained personnel for single-mode installation.

I would never recommend ripping out current cabling if it meets the user’s needs, but when a network needs upgrading and the cabling is inadequate for that upgrade, removing older multimode fiber, or UTP copper, and replacing with it single-mode fiber probably means that will be the last cabling upgrade ever needed.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor

Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.

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