By Paula Bernier
When Williams Network was looking to build a new nationwide network, after selling off
all but one fiber strand of its original network to WorldCom Inc. in 1995, the company
knew it was going to cost them.
But because of advances in asynchronous transfer mode (ATM) and optical technology, the
buildout will be far less painful than Williams had originally envisioned.
Rather than installing separate synchronous optical networking (SONET) add/drop
multiplexers (ADMs) to pull access traffic on and off of SONET links, and digital
cross-connects (DCS) for traffic grooming, concentrating traffic and bandwidth allocation,
Williams decided to install Ascend Communications Inc.’s GX 550 Smart Core ATM switches.
These switches are among a new breed of equipment that integrates SONET ADM and DCS
capabilities into the switch. Because Williams doesn’t have to invest in separate DCSs (a
40 percent savings, in Williams’ estimation) and SONET equipment (an estimated 40 percent
to 45 percent savings), Williams expects to save up to 85 percent on its network capital
costs as a result of the new, integrated equipment, says Wayne Price, manager of
technology development at the carriers’ carrier.
"We were actually prepared to pay more for this network. When we saw the 80
[percent] to 85 percent [savings], it was almost beyond belief," says Price.
Consulting company BancAmerica Robertson Stephens says a DS-3 link on a traditional
network would typically require a $3,906 digital cross-connect, a $2,917 SONET ADM and a
$1,416 backbone ATM switch. By eliminating the DCS and the SONET ADM switch with this new
architecture, a company can realize a savings of about 75 percent, according to
BancAmerica Robertson Stephens.
In addition to lower equipment costs, integrating cross-connect and muxing capabilities
in with routers and switches can result in more reliability and more efficient use of
physical space in equipment offices, where space is at a premium, says Michael Arellano,
analyst with Degas Communications Group Inc.
"We’re removing network elements so there are fewer points of failure," says
An integrated approach also means Williams doesn’t have to employ special "SONET
and [digital access and cross-connect system] guys," Price says.
The switches will also enable Williams to reconfigure private lines within a few
minutes, which is far faster than is allowed with today’s digital cross-connects, say
Price and Kiel.
Ascend and Williams last month launched a live field trial on the Williams network
between Washington and Atlanta. They also are working with dense wave division
multiplexing (DWDM) vendors Pirelli Cables & Systems Worldwide and Ciena Corp. to do
interoperability testing between their DWDM equipment and Ascend’s GX 550 switch. The
testing focuses on error-free transmission by the DWDM systems, path protection by the GX
550 and successful management of performance monitoring between the two systems.
According to Jeffry Kiel, Ascend’s director of product marketing, data switches offer
as much protection as SONET does.
"All the interfaces are the same and the functionality is the same, it’s just
different plumbing," says Kiel, noting that SONET line cards plug into the switch.
SONET capabilities also can be integrated into the DWDM gear that Ciena Corp. sells, adds
Denny Bilter, director of marketing for Ciena.
"SONET is really a redundant layer. It’s not necessary," he says.
That’s a controversial statement.
While SONET is designed to reroute traffic within 50 milliseconds of the outage in the
event of a fiber cut, it typically takes ATM switches between 300 and 500 milliseconds to
do that restoration, says Randy Eisenach, marketing manager for SONET at Fujitsu Network
ATM does some restoration in small networks, adds Kathy Szelag, vice president of
marketing for Lucent Technologies Inc.
"If you took a bank’s ATM network with a few sites, ATM could restore [a fiber
cut] by finding an alternate path," Szelag says. "But if you used a network with
thousands of fibers and thousands of nodes, it wouldn’t be able to do it fast
According to Eisenach, eliminating the SONET layer just results in higher fiber costs,
making any savings from eliminating SONET equipment a wash. The three cost components in a
transport network are the ATM equipment costs, fiber costs and SONET transport costs,
Eisenach explains. Eliminating the SONET layer dramatically increases the fiber count and
costs, because the ATM switches then have to be deployed in a meshed network (so ATM
switches are each interconnected by fiber–much like a spider web–rather than just with
the ATM switches on either side of them), so the number of connections between the
switches grows exponentially.
"That’s a key element that the ATM guys don’t really put in the press bulletins
they put out," says Eisenach.
But Williams’ Price asserts "the ATM to optical interface is really
The companies expected to begin field trials of the integrated equipment in July.
Williams, which has bought 68 GX550s, committed to buy $150 million in Ascend equipment
within the next three years.
"That number is meaningless," however, says Price. "We’re going to blow
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January 21 2020 @ 19:35:32 UTC