Bandwidth needs spur fiber diversity

Bandwidth needs spur fiber diversity

Paul Palumbo

As a carrier`s carrier, IXC Communications in Aus tin, TX, regularly leases capacity to major long-haul providers to ensure both "route diversity"--running cable through unfibered regions--and support of growing bandwidth-intensive requirements from Internet service providers.

Demands for bandwidth include voice, data and video traffic (see Lightwave, January 1996, page 1). To meet this rising demand for route-diverse bandwidth, IXC has installed more than 1200 miles of fiber this year. The company is projecting total network expansion by more than 4000 fiber-miles to be completed by year-end 1996. In total, IXC has committed about $600 million to fund its two-year construction plan.

Ken Hinther, IXC vice president and chief operating officer, says that growing demand for bandwidth from the big four carriers (AT&T, MCI, Sprint and GTE) is fueling network expansion. "Some of that demand can be provided via their own networks, and some has to be leased from other carriers, like IXC," Hinther says.

IXC turned up its frame relay Asynchronous Transfer Mode (ATM) network in September, and, if construction goes according to plan, fiber routes from Cleveland through the Ohio Valley, down to Chicago and Dallas, then out to El Paso, Phoenix, Tucson and Las Vegas are expected to be completed this year. Fiber routes running from Las Vegas into Los Angeles, and from Cleveland into New York and Boston are scheduled to be completed before the end of 1997. Routes from New York through Atlanta, back to Houston and on to Florida are expected to be turned up in 1998.

Phase one of IXC`s network build is essentially an overbuild of an existing microwave system. Phase two construction is planned to expand the company`s network in the Southeast and create diversity from phase one.

The third phase is designed to expand along the West Coast. With demand for capacity rising, IXC is evaluating expanding phase two into a much more extensive build than called for in the original plans, according to Hinther. If completed, that would require an additional 3000 route-miles of fiber to be installed. Originally, the company had planned to lay some 9000 route-miles of fiber.

IXC is deploying Alcatel Synchronous Optical Network technology from Dallas going west and is using Northern Telecom equipment from Dallas going north. Hinther says that IXC is using Alcatel`s fluo ride-fiber amplifiers, which are OC-48 capable at speeds to 2.5 Gbits/sec (see Fig. 1). These amplifiers operate in the 1500-nm range, but IXC stacks light signals through 16 channels. Total capacity is boosted to 38.4 Gbits/sec by packing 16 OC-48 lines per fiber pair.

Going north, IXC is using Janus amplifiers from Northern Telecom. They also operate at 1500 nm. IXC has designed the network so it can supply multiple OC-192 capacity. It can deliver capacity out of a network interface ranging from DS-3, at speeds of 44.736 Mbits/sec; OC-3 at 155 Mbits/sec to OC-12 at 622 Mbits/sec; and up to OC-48 speeds (see Fig. 2). Hinther explains that IXC can drop any increment of capacity from DS-3 up, based on what needs to be handed off at terminal or junction points.

The company typically installs 48 fibers for its own use, plus whatever else is required by its partners. The number of fibers depends, in some measure, on the partnerships IXC builds along the way. For example, a "rights-of-way" deal might specify that IXC allocate dark fiber for a particular partner.

During initial network turn-up, IXC uses only four fibers. That leaves 44 fibers for expansion and more than enough dark fiber for prospective rights-of-way deals. However, IXC could also exchange some of those dark fibers for additional routes.

In some areas of the country, especially in the western United States, IXC is using fiber-optic ground (FOG) wire on top of high-power transmission lines. This method of deployment does not, however, alter rights-of-way partnerships. Hinther says that, in certain areas of the build, FOG wire has proven to be more reliable and less susceptible than typical buried wire to outages such as backhoe fades. "In the western part of the United States, ground wire is truly diverse to existing areas, and IXC can sell that diversity to the other carriers," Hinther notes. IXC is not using FOG wire in all parts of the country because icing and bad weather adversely affect its performance.

Getting fiber into the ground (or strung on towers) is the most labor-intensive part of IXC`s construction, accounting for as much as 80% of new build costs. Equipping the fiber with electronics accounts for 20% of total construction costs.

According to Morgan Stanley analyst Peter Kennedy, the fact that IXC is putting in dispersion-shifted fiber is a big advantage for the company. "Average fiber construction is running about $80,000 to $100,000 per mile, but IXC is coming in at about $60,000 to $65,000 per mile," Kennedy observes.

The fiber cable deployed by IXC is Corning LS fiber or AT&T TrueWave fiber. Both are non-zero-dispersion-shifted fiber. Coupled with wavelength-division multiplexing technology, the additional 44 fiber strands give IXC latitude to grow its network capacity without approaching fiber exhaust levels. Using Alcatel and Northern Telecom electronics, IXC`s network is designed to carry more than one-half million conversations on a single fiber pair.

Hinther says that non-zero-dispersion-shifted fiber provides a cost advantage over older fiber in the ground. He notes that repeater spacing can be increased to 45-mile increments, as opposed to 25 miles with the older fiber. Moreover, IXC doesn`t have to install equipment to compensate for light-pulse dispersion. The company estimates that it is saving 30% to 50% on the cost of equipping the fiber. q

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