On the LAN

Premises cabling to support phones and PC networks hasn’t really changed much since it was first standardized by TIA-568 around 1990; It has just become faster, and Ethernet local-area networks (LANs) are now a thousand times faster. Plain old telephone service (POTS) has migrated to voice over Internet protocol (VoIP) on Ethernet LANs. Enterprise networks are now expected to also transport digital video at high bit rates. Even wireless access points, the preferred method of connection for many users today, have become so fast they require gigabit connections to support their speed.

These changes in communications over premises cabling have forced users to incrementally upgrade not only their networking equipment, PCs and phones, but also their cabling. Many companies have already replaced all copper cabling systems with systems using fiber optic backbones, unshielded twisted-pair (UTP) copper to the desktop and wireless access points. Companies with new buildings or facing network upgrades must decide on what the next upgrade technology should be.

A new type of computer LAN that uses a fiber optic cable plant has become an option for updates and new systems. Called a passive optical LAN (POL), it promises significant savings in cost, energy consumption and space for enterprise networks. It will also affect the practices of contractors who install premises networks today using either copper or fiber cabling.

This new option to traditional structured cabling is already causing some users to reconsider their options. One can now install a “triple-play” system with voice, data and video, which is based on the consumer technology now used for fiber to the home (FTTH), at a significantly lower cost than traditional LANs.

Economics is, as usual, the driving force. FTTH uses optical splitters (hence the term passive optical network or PON), instead of electronics switches, to connect many users over a single fiber. Using splitters greatly reduces the costs of both electronics and fiber optic cabling. The low cost of FTTH has already led to 5 million U.S. homes being connected with fiber optics and many times that number in the rest of the world.

The cost of the PON hardware used in FTTH, as well as the cost of installation, continues to decline, since high volume for FTTH hardware has driven costs down fast, as with all electronic systems. Innovations, such as using prefabricated cabling systems, have also contributed to reducing installation costs.

Where connecting a home with fiber would have cost thousands of dollars until recently, the cost is now down to a few hundred. The lower cost of FTTH, combined with the increasing cost of maintaining aging copper networks, has led some telephone companies (such as Verizon) to make a 100 percent commitment to fiber—no more copper—for their phone systems.

The technology developed for FTTH in multidwelling units (MDUs)—such as condos or apartments, where users are close together in a single building—has allowed particularly large cost savings. Prefabricated cabling systems, combined with new bend-insensitive fibers, allow easy installation in tight spaces, greatly reducing installation costs.

If you want a converged LAN, what could be better than the technology developed for triple-play (voice/data/video) MDU FTTH? It offers some compelling advantages. It is proven technology, gigabit-fast, cheap and easily upgradable, since it runs on a single-mode fiber cable network with virtually infinite bandwidth. The short distances allow 64 stations to share one GPON (gigabit PON, an international standard) link, and these can be integrated into systems with thousands of users, just like a city.

The advantages don’t stop there. Desktop units similar to the optical network terminal used at the home connects on a single fiber to allow connections for multiple (four to 24) users with Ethernet speeds of 10/100/1,000 Mbps. Equipment is even available for those still using analog POTS phones. Managing the network is centralized, and security is handled with encryption for all users.

The cable plant architecture is similar to a TIA-568 centralized fiber-cabling system. But instead of multimode fiber, it uses single-mode fiber, and a good portion of signal distribution is done not by electronic switching but by passive optical couplers, which has the further advantages of reducing power consumption and enhancing reliability.

The shared-fiber architecture of a PON minimizes the cabling needed and, like any centralized fiber architecture, gets rid of the electronics, cooling and grounding needed in a telecom closet. You don’t even need the closet at all.

The system approach used in these PONs lends itself well to prefabricated cabling systems that just require placing cables and plugging in modules. No field termination of fiber is needed at all. The only copper cabling is patchcords to connect PCs or wireless access points to the desktop workgroup terminal.

A complete system using this concept cannot only cost less than fiber to the desk, but it can cost less than Category 6 to the desk, too. Of course, it can also support the mandatory wireless access points required in today’s enterprise network and hardware is available to support power over Ethernet devices.

In case you think all this is new technology, the first fiber optic LANs used passive coupler technology instead of electronic hubs in the 1980s. The big pitch for them was not cost, but the reliability of a passive network. Motorola reintroduced this concept using FTTH PON components less than a year ago, and Verizon has been selling it to large users—very successfully, it seems. It even has that new acronym, POL, for passive optical LAN.

The success of PONs in MDUs has inspired another application for PON or POL technology: enterprise LANs. These LANs have become an applications for triple-play just like the home, merging LAN data and Internet connections with voice in the form of VoIP and adding video for videoconferencing (and maybe downloads of some entertainment on the corporate network, too.)

The POL is a cost-effective potential game-changer for enterprise LANs. It uses single-mode fiber, making it basically infinitely expandable, not only for higher bandwidth networks but to connect on outside plant fiber to other locations in larger geographic areas, making it an ideal solution for metropolitan networks.

What does this mean for contractors? Installing these systems is obviously different than installing traditional structured cabling. Prefabricated fiber optic cabling systems are easy for the contractor to install and have already been gaining in popularity for all premises fiber optic installations.

If the cabling is installed and terminated on-site, the traditional way, the recommended termination method for single-mode fiber is fusion-splicing pigtails onto the fibers in the cables. On short cables like these, it’s important to reduce the reflections on the connectors, so only low-reflectance connectors like ultra physical contact (UPC) or angled physical contact (APC) connectors are used, depending on the equipment requirements.

The contractor will need to invest in good fusion-splicing equipment and installers will need to be skillful at fusion splicing, perhaps requiring additional training.

Installing prefabricated cabling for the systems is easy. Cables and connectors have been developed for FTTH that are rugged and easy to pull. Bend-insensitive fibers allow installers to run cables in places that regular cables could not be run, such as inside modular furniture, where tight bends are encountered.

Cabling systems will still need careful handling to ensure not damaging cables or connectors. Cleanliness is even more important since POLs use single-mode fiber. Specks of dirt are large compared to the tiny core of single-mode fiber and can greatly affect connector loss and reflectance.

Finally, testing single-mode systems is easier than multimode, but equipment for single-mode insertion loss testing will be required.

There is one extra thing to remember on POL installations. All that old copper cabling is now obsolete, so before installing the new fiber cabling, it should be removed and scrapped.

HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.JimHayes.com.

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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