New distribution frame: higher density without more congestion

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The latest product release from Telect Inc. (Liberty Lake, WA) isn't flashy. It's not tunable, it doesn't use mirrors, and it's not likely to appear in market studies from top analyst firms. While Telect's ultra-high-density advanced distribution frame (ADF) may not be the "sexiest" part of the network, its function is critical for managing and protecting fiber-optic cables and the high-value traffic and services they carry.

A distribution frame is the centralized point of access and maintenance for fiber connectivity coming in and out of a building. It is the "nerve center" for fiber-optic cables and signals, the point of interconnection between active network elements, such as optical switches and DWDM equipment. The distribution frame is also the point at which carriers and service providers make cross connections between their facility and their customers' facilities, and for this reason, the folks at Telect turned to the service providers for input regarding the ADF's design.

"We asked them, 'How fast is it to make a crossconnect? How user-friendly is it? How easy is it to deploy? How much floor space does it take up?' A number of factors of cost and weight and size and protection-all those things were benchmarked," explains Buddy Reeves, senior product manager.

Telect also examined market trends, looking at where companies like Cisco, Sycamore, and Juniper are headed. The company determined that its new distribution frame would have to support higher power levels, more wavelengths, and higher data rates.Th 1807lwe200

Telect's advanced distribution frame features a tray-based architecture on the right and left sides with a split vertical cable-storage channel in the center, which minimizes cable congestion within the frame.

Increased density proved to be the industry's most immediate need, however. Higher port density is critical, says Reeves, because many service providers average more than 24 distribution frames per office, and they are simply running out of space. The ADF enables 2,304 terminations in a 26-inch-wide frame using small-form-factor LC connectors, which equates to more than 530 terminations per square foot of floor space. Using SC connectors, the ADF enables 1,536 terminations in a 26-inch-wide frame, or more than 350 terminations per square foot. The ADF is also scalable and can house as few as 72 terminations, depending on the user's need.

Increasing port density can cause significant problems, however, and may result in tangled cables, unidentifiable circuits, and overwhelming congestion-all of which plague existing distribution frames. Many of these frames were de signed "before the bandwidth explosion," explains Reeves, "before all of the 10 Gbits times 70 or greater wavelengths per cable. Now people are very aware of the fact that you want to protect that cable-it is carrying millions and millions of dollars in services-and you want to make it easy to get to and easy to use."

The ADF provides circuit protection through its tray-based architecture, which limits the number of ex posed ports to six or eight at time, which is the number of interconnection points housed in a single tray. Trays are positioned in groups of 12, 16, and 24 and run along the right and left sides of the frame. The company's Invisi Manage sliding mechanism prevents movement and tension of the cable while the trays move from fully open to closed positions. In the center of the frame is a vertical cable-storage channel, which houses the slack cable used to connect points within the frame.

The ADF features a total front access design, which allows the user to place the frame up against a wall, thereby saving precious central office space. Because the frame does not require simultaneous front and rear access, only one technician is necessary to provision a circuit.

In addition to protecting the cable, the ADF is also designed to protect the end user. According to Reeves, at least four of Telect's customers were concerned about increasing power levels. In a typical SONET system, power levels did not exceed the 200- to 250-mW range, but some of today's new equipment uses Class 4 optical lasers, which operate in the 5-W range. To protect the user from laser radiation exposure, Telect has designed the ADF so that all the trays pivot away from the user; the laser radiation points in toward the tray face. Telect is also in the process of having its trays burned to see just how much radiation they can withstand.

Another critical feature of the ADF is its 30-mm or greater bend-radius protection, which is the industry's recommendation for protecting high-bandwidth fiber in high-density environments to prevent degradation of the signal and alleviate physical stress on the cable itself.

"That was really a design criteria of the ADF," explains Reeves. "No part of the frame where cable runs, whether it is the multifiber cable or the single patch-cord cables on the front or anywhere on the rear of the frame, nowhere will those cables ever exceed that bend radius."

The bend-radius protection allows the ADF to be "futureproof," claims Reeves. As the industry moves to higher optical frequencies-such as the L-band or 1,600-nm window-the bending of the cable becomes more critical. In addition to causing physical stress that can damage the fiber, violating the 30-mm bend radius in the L-band affects the overall optical performance of the network. Attenuation of the signal in this window is subject to "the hockey stick effect," says Reeves. High attenuation leads to signal loss, which leads to the need for more amplification, which adds expense to the network.

"We're to the point now where we think our design took into account newer technologies as they were coming out," asserts Reeves. "We feel like maintaining the bend radius is one of those things that really futureproofs our product and positions it well for next-generation technologies that we don't even know are out there yet."

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