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Connectors improved.


The first round of the fiber-optic shakeout offers good news about products for fiber-based LANs and premises wiring.

Only a few years ago, this emerging technology presented a range of bewildering choices as manufacturers offered an array of incompatible products in the absence of formal or de facto standards.

Cable manufacturers forcefully debated the comparative merits of 50/125, 85/125, 62.5/125, and 100/140 multimode fibers for LAN and other applications.

A variety of connectors were offered, each with performance, ease-of-use, and compatibility issues for the user to evaluate.

Today the situation has changed. Every major LAN topology has a fiber-optic alternative, while the Fiber Distributed Data Interface (FDDI), designed specifically for fiber, is a high-speed backbone LAN.

Bridges provide the transition between copper and optical legs of the LAN.

The 62.5/125 fiber has emerged as the fiber of choice, with the 50/125 fiber running a distant second and 85/125 fiber nearly forgotten. The 100/140 fiber still retains popularity in some applications, and every connector available for 125 multimode fiber has a counterpart for 140 fiber.

Better Cables

At the same time, cables have matured, making it much easier for the user to specify the cable suited to his application.

One can routinely specify general purpose, riser, or plenum cable, with mechanical and flammability specifications matched to the application.

In addition, off-the-shelf availability of fiber-optic transceivers, couplers, and such accessories as wall/floor outlets and distribution panels simplifies the packaging of the LAN in the building.

In fact, many new buildings are being constructed with the fiber in place, even in the absence of immediate plans for its use.

Finally, two standard types of connectors have surfaced from the pack as the preferred choice for LANs and premises wiring: the ST-style and the FDDI-compatible.

Connectors that emerge as standards are usually designed by major companies in the industry, with the research and manufacturing resources and the marketing skills to popularize the design.

The ST connector was designed by AT&T for use in its premises wiring system.

Similarly, the FDDI-style connector is based on a design by AMP Inc. to fill the requirements listed by the ANSI X3T9.5 FDDI committee. Both connectors are based on a 2.5mm-diameter ceramic ferrule, itself becoming a standard in fiber-optic connectors.

The ST is a single-channel connector using a spring-loaded bayonet coupling.

Among the features that have helped the ST connector supplant FSMA connectors as the industry standard are lower insertion loss, and the quick-release bayonet coupling in place of the multiturn threaded coupling.

The ST-style connector also contains fewer separate parts. In particular, the tiny alignment sleeve of 906-style FSMA connectors is a part easily lost.

The FDDI connector is a two-channel connector using side latches for a quick-connect capability with audible and tactile feedback of the latching. A fixed shroud protects the ferrules.

Four different field-installable keying combinations are offered per the FDDI specification, and polarization prevents transmitting and receiving lines from being crossed.

The connector is designed for the high-end 100-Mb/s FDDI LAN but is widely used in other applications.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:for fiber-optic networks
Author:Hess, Dennis; Himes, Jack
Publication:Communications News
Date:Nov 1, 1990
Previous Article:The wireless option.
Next Article:Hospital's broadband LAN poised for future.

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