OC-192 runs coast to coast

July 1, 1997

OC-192 runs coast to coast

paul palumbo

Qwest Communications Corp., Denver, CO, has installed approximately 5000 miles of conduit to support a planned 13,000-mile national fiber-optic network deployment scheduled to culminate in 1998. Along the way, it will become the first company to use 10-Gbit/sec OC-192 exclusively throughout its network backbone.

The company`s network is divided into geographic zones and incorporates a Synchronous Optical Network (Sonet) ring topology. Each zone will be served by a 4-fiber, bidirectional system capable of delivering up to 80 Gbits/sec of transport capacity. Bidirectional transport can take place over both nonzero-dispersion-shifted fiber and singlemode fiber.

The company plans a ring connecting Denver, Houston, TX, and Kansas City, MO, along with eight other rings moving from west to east across the country (see figure on page 20). Rings in Seattle, WA, and Boston have yet to be closed. The network is currently illuminated between Los Angeles and Sacramento, CA, and between Dallas and Houston.

Nortel`s OC-192 Sonet electronics drive the network, with the addition of Nortel dense wavelength-division multiplexing (dwdm) features, to push fiber transport rates up to 80 Gbits/sec per fiber. Qwest recently announced a $150 million purchase of Nortel network electronics--the company`s largest order of OC-192 Sonet equipment to date.

The network costs about $100,000 per mile, and the total implied cost of Qwest`s OC-192 national backbone is approximately $1.3 billion. Qwest is funding the deployment through sales of dark fiber, proceeds from its pending initial public offering of stock (about $118 million out of an expected $242 million), and placement of long-term notes. Qwest is typically installing 96-fiber counts and reserving 48 fibers for future use. The company has sold dark fiber to Frontier Corp., WorldCom, and gte.

"Qwest started with a blank sheet of paper and then set out to build the most efficient, robust system available," according to company spokesperson Tony Brodman. "Qwest was going to build a new network, and it made sense to deploy state-of-the-art technology and not something older that would have to be retrofitted later on."

Qwest sells communications services to three primary customer segments: interexchange carriers, commercial businesses, and consumers. Among its customers are Sprint, mci, at&t, WilTel, and Internet service providers. The company also provides residential telephone services through a network overlaid on its fiber plant. Internet service provider backbone growth is expected to be tremendous over the next few years, and bandwidth wholesaling is forecast to gobble up much of the network`s capacity.

High bit-rate traffic

Qwest is installing Lucent Technologies` TrueWave nonzero-dispersion-shifted fiber because it is better suited to higher-bit-rate traffic. Fred McClimans, an analyst with Current Analysis, in Ashburn, VA, says that a key feature of this type of fiber is that it handles high bit rates more cost-effectively. McClimans emphasizes the "growing capacity of lans [local area networks] has created an even greater demand for backbone bandwidth."

In addition, nonzero-dispersion-shifted fiber lets providers increase reach between OC-192 system components. Compared to OC-48 (2.5-Gbit/sec) systems, this reduces the number of necessary amplifiers by 25%, according to Serge Melle, senior marketing manager at Nortel. Qwest is placing optical repeaters in 60-mile increments, on average, except when cities are close to each other.

As networks transport more and more data-centric traffic, quality and performance have become important issues. Melle says voice transmissions can contain a certain number of disruptions and still sound the same. For data transmissions such as Asynchronous Transfer Mode, "if one `zero` and one `one` are confused in the transmission, the whole transmission has to be resent," he says.

Nortel has created a new feature for OC-192 Sonet called "forward error correction," which improves bit-error rates. Compared to OC-48, which guarantees 10-12 bit-error rate transmission, OC-192 provides 10-15 end-to-end performance--a 1000¥ improvement. Errors are self-corrected before the transmission reaches its destination, thereby avoiding costly and time-consuming retransmissions. Nortel developed the technique, but other vendors are also implementing forward error correction features into their Sonet solutions.

dwdm configuration

Qwest is using Nortel`s dwdm configuration, which means wavelengths conform to International Telecommunication Union standards to better ensure future scalability. Nanometer ranges are between 1530 and 1560, appropriate to each of the erbium-doped amplifiers. To implement bidirectional transmission, the nanometer ranges are split into four wavelengths, with two operating in one direction, and the other two in the opposite direction. The 80-Gbit/sec capacity per fiber pair translates to 40 Gbits/sec in each direction.

The market is moving toward optical interconnects between carriers and crossconnects. Melle says the OC-192 platform is built to accommodate that transition; it connects to other customers` networks and equipment at rates of OC-3 (155 Mbits/sec), OC-12 (622 Mbits/sec), and OC-48. Crossconnect vendors such as Tellabs have introduced OC-12 and OC-3 ports. Such configurations are less expensive, use less space, and provide the benefits of Sonet networking. q

Paul Palumbo writes from Seaside, CA.

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