Record fiber-count cable fits in Manhattan ducts

Record fiber-count cable fits in Manhattan ducts

george kotelly

Under a multimillion-dollar contract, Lucent Technologies, assisted by Antec Corp., Rolling Meadows, IL, is delivering 50 miles of singlemode, 288-fiber-count AccuRibbon cable to cable-TV operator Time Warner Cable of New York City for transporting high-bandwidth video, voice and data communications services to Manhattan subscribers.

The specially designed Lucent Technologies-Bell Laboratories` ribbon cable represents the highest-fiber-count ribbon cable installed to date. Essentially, it consists of a central-core tube surrounded by water-blocking tape, dielectric strength members, rip cords, an inner sheath, a metal armor sheath and a polyethylene jacket. The core tube contains 12 ribbon sections, with each section holding 24 depressed-clad optical fibers--a technology first, according to Lucent officials (see Fig. 1).

The 0.9-inch-diameter ribbon cable is being pulled through restricted 1.25-inch diameter duct spaces inside crowded underground Time Warner Cable conduits using standard capstan methods and intermediate assist capstans. At press time, approximately eight miles of ribbon cable had been installed.

"Time Warner Cable is trying to install the largest amount of fiber possible in as small a cable space as possible so the company can optimize underground duct space and increase its network bandwidth capabilities," says Nina Aversano, Lucent Technologies` global commercial markets president.

The 288-fiber-count ribbon cable is supporting Time Warner Cable`s hybrid fiber/coaxial-cable (HFC) network in Manhattan, which employs numerous optical nodes that connect to approximately 500 to 1000 homes (see Fig. 2). The HFC network passes about 150,000 homes now, but during the next five years, the network is anticipated to pass about a million homes in Manhattan, Queens, Staten Island and Brooklyn.

States Pete Wagener, vice president at Antec Network Technologies, which is Lucent`s primary distributor of products to U.S. cable-TV customers, "Time Warner`s Manhattan network architecture requires extremely high fiber counts for the initial phases of the build. The architecture is complicated by having limited duct space available, necessitating a cable design that meets Time Warner`s fiber-count requirements in a single cable sheath."

To achieve fast and cost-effective high-fiber-count connectivity, updated mass fusion splicing technology is being implemented. According to Lynda McHale Kane, business manager for network cable system products to global commercial markets at Lucent Technologies, Norcross, GA, "Mass fusion splicing can now splice 12 fibers at a time. More important, the 12-fiber splice loss is essentially equivalent to the splice loss for a single-fiber fusion splice. In fact, splicing 12 fibers rather than one fiber at a time with low loss has improved time productivity by a factor of 4 to 1 and installation costs by a factor of 2 to 1. And these numbers are expected to continually improve."

Limited duct space

"Our duct space in Manhattan is extremely limited, and Lucent`s custom-designed cables allow us to use what we have and avoid installing or acquiring new duct," remarks Larry Pestana, vice president of engineering at Time Warner Cable of New York City. "Mass fusion splicing these cables, rather than splicing each fiber individually, will save us time and money in bringing this cable project to fruition."

"Refinements in ribbon fiber cable and mass fusion splicing techniques have improved such that mass fusion splicing now more readily meets overall network splicing requirements," adds Antec`s Wagener. "Using mass fusion splicing will bring high splice integrity and substantial splice cost savings to this project."

The lack of duct space is a major problem under Manhattan, and Time Warner Cable needed a high-density fiber-optic cable at a one-time installation cost that would meet both short-term and future communications services. The cable also had to be rugged to withstand the tight and harsh installation environments under New York City streets. In fact, the cable requirements called for a diameter of less than one inch to allow pulling space, and a metallic armor sheath for strength and protection. Says Tom Walter, manager of optical fiber and cable at Lucent Technologies, "Standard cable materials were used, but the dimensions were tight. The armor is made of electrically chrome-plated steel, and the central-tube cable design gets its strength via an outer armored sheath." Despite the tiny duct space, the ribbon cable installed easily without any problems.

"A 288-fiber-count ribbon cable was selected because of the high fiber density required and because it could be mass fusion spliced," remarks Pestana. "Splicing single fibers in one location would be prohibitively time-consuming and expensive."

Adds Lucent`s Kane, "The 24-fiber ribbon cable is a leapfrog in technology. The industry standard is 12 fibers to a ribbon."

12 fibers at a time

Technology improvements in fiber geometry, ribbon cables and mass fusion splicing machines have all reached the point where mass fusion can now splice 12 fibers at a time. Therefore, in the Time Warner network, each 24-fiber ribbon cable has to be split in two for splicing 12 fibers at a time.

Commenting on high-fiber-count technology, Lucent`s Walter declares, "Since the delivery of the 288-fiber ribbon cable, the company has been able to jump the count to 360 fibers. The higher count is commercially available now, and the fiber count is expected to increase again by the end of this year."

In fact, adds Kane, "Another cable-TV company has already placed an order for the 360-fiber cable. Cable operators have moved quickly with fiber deployments during the past four years. They have moved rapidly up the learning curve; are receptive to new ideas, ways and technologies to increase the fiber installed in their networks; and readily seek assistance from suppliers for cable installation help. They are also cooperative on installation needs, requirements and upfront meetings, and are willing to take risks."

Multimedia services

"As for planned Time Warner communications services, just regular video delivery will be provided initially," cites Time Warner`s Pestana. "Plans are in the works for telephony and data services, the use of cable modems for Internet access, and video-on-demand and other similar services, but all services will be determined from a business sense."

The specific network transmission bands are going to vary depending on the availability of affordable electro-optic converters. To handle additional analog communications, Time Warner`s present 550-MH¥video spectrum is being expanded to 650 to 700 MHz. The spectrum goal is 860 MHz, with the top 200 MH¥reserved for digital video, telephony and data services.

The fiber-based network is also expected to be pushed closer to the customer. It will have a maximum of three radio-frequency (RF) amplifiers, three line extenders, from the optical node over coaxial cable to the farthest subscriber. In some of the large New York City buildings, as telephony services are made available, both twisted-pair copper wires and coaxial cable could be used depending on the building layout. In fact, in some high-rises, the media might carry separate services, such as entertainment on coaxial cable and voice on twisted-pair cable.

Time Warner has installed fiber in New York City since the late 1980s for interconnects and backbone distribution. The company had previous experience with Lucent`s 216-fiber ribbon cables for carrying commercial voice services in New York City. The company is using more fiber to reduce the number of cascade amplifiers needed; the amplifiers are emplaced in a basic tree-and-branch architecture.

"Pushing fiber closer to the customer in Manhattan is restrictive because of cost conversion," says Pestana. "In Manhattan, Time Warner has an optical node in the basement of a building in nearly every block, just a few thousand feet from the customer. Because this setup is already close to the customer, there is no present need to get closer," he notes.

Time Warner estimates that 60% of its customers are within the range of the first RF amplifier from the optical node, thereby achieving high network reliability. The connection cost per customer ranges from $500 to $1000, depending on the price of the support electronic boxes.

Interactive video services are still considered futuristic by Time Warner. Its upgraded New York City network can accommodate interactive services, but content, delivery and set-top box costs remain too high for now. According to Pestana, the HFC network build is under way, but won`t be completed until next year. Then, advanced communications services will follow over the next few years. q

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