Must-read. Data Sees the Light Lay Down Your SONET Muxes, Cast Off Your Cross-Connects [ASND/WMB references]
Excerpt: "By using Ascend Communications Inc.'s GX 550 Smart Core
ATM switch, which has an integrated SONET line card, service provider
Williams expects to save up to 85 percent on its network buildout costs,
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."
x-changemag.com
By Paula Bernier
With the incredible growth in data traffic, companies are reassessing how
to manage and design networks, which in the past were created for
voice. As a result, data equipment such as switches and routers are
converging with synchronous optical networks (SONET) and wave
division multiplexing (WDM). Ultimately, this path is expected to lead to
a promised land called the all-optical network.
"Optical switches of the future will switch light," says Mat Steinberg,
director of optical networking with consulting firm Ryan Hankin Kent Inc.
In the "very far future" the world is moving toward photonics, adds
Randy Eisenach, marketing manager for SONET at Fujitsu Network
Communications Inc.
"This is more than short-term planning. It's not two to four years, it's
more like seven to 10 years," Eisenach says.
Whatever the timeline, optical technologies and data are quickly
becoming more closely aligned.
Many routers already have OC-3, OC-12 and are coming out with
OC-48 interfaces, which plug into SONET add/drop multiplexers.
"We introduced packet over SONET solutions two years ago. Our 7500
and [12000] gigabit switch routers do packet over SONET," says says
Graeme Fraser, vice president of engineering and general manager of the
optical internetworking business unit at Cisco Systems Inc.
Silicon vendors such as Lucent Microelectronics and PMC Sierra are
building packet-over-SONET capabilities into their framer chips, he
adds. Lucent Technologies Inc. also has direct local area network (LAN)
interfaces to its SONET gear and recently announced a SONET Internet
protocol (IP) router, says Kathy Szelag, vice president of marketing.
"You couldn't have done that in the past," she says.
Despite what would seem a straightforward issue, placing asynchronous
transfer mode (ATM) or IP onto SONET is no easy task, says Szelag.
Lucent and Cisco worked together to overcome some of the barriers.
For example, both IP and ATM have scramblers that prevent long strings
of 1s or 0s that could create an outage, she says, but optical systems
look for transitions between light and dark--dark is 0 and light is 1. So
the two scramblers can cancel each other out. Cisco and Lucent helped
work on standards to allow the scramblers in IP and ATM to work with
the scramblers in SONET, she says.
Of course, since its core business is selling IP routers, Cisco believes that
mapping IP onto SONET, without an in-between ATM layer, is the way
to go.
"The reason people are discussing [packet over SONET] is it's a more
cost-effective and efficient way to move IP across a backbone. You no
longer need an ATM backbone with it," says Fraser.
In the past, IP links tended to be low-speed, so carriers would
encapsulate IP into ATM cells at OC-3, then mux OC-3 links up to
higher OC rates to go over a backbone. But as IP traffic grows, IP links
are higher speed and don't require that extra layer, he says.
Traditional telecom vendors, which tend to support ATM over SONET,
also are coming out with new products that put data directly onto
SONET.
Siemens Public Communication Networks Group's TransXpress ALine
allows direct transmission of broadband ATM signals, as well as
narrowband signals, onto SONET. The product allocates bandwidth in
64 kilobits per second (kbps) increments up to 150 megabits per second
(mbps).
Michael McLaughlin, vice president of transport networks, says ALine
reduces by 30 percent the overall network costs of transporting data
over SONET by providing efficient interfaces to switches, and allowing
for higher use of SONET ring capacity.
"For example, if a customer needs 10mbps today the carrier has to
support that with a DS-3 (45mbps), so 35mbps is unused for that
customer. Plus it ties up ports unnecessarily on ATM switches," says
McLaughlin. "Our product is at the customer interface when you take the
10mbps onto the ring. Multiple customers' traffic is aggregated on the
ATM switch."
Some of the newest gear actually integrates SONET functionality into
routers and switches, eliminating the need for separate SONET add/drop
multiplexers and digital cross-connects.
Lucent in the third quarter expects to make generally available an
integrated product it calls the WaveStar Bandwidth Manager.
Self-healing ring interfaces within the WaveStar Bandwidth Manager
integrate traditionally separate network elements such as standalone
add/drop multiplexers; broadband, wideband and ATM digital
cross-connect systems; and ATM and IP core switches and routers.
"Lucent can have a fiber coming into a [central office] at OC-12, hit the
WaveStar Bandwidth Manager, which has IP and ATM fabrics and
SONET/TDM (time division multiplexing) fabrics, and come out at
OC-12 again. It has very nice management capabilities," says Michael
Arellano, analyst with Degas Communications Group Inc.
Integrating cross-connect and muxing capabilities in with routers and
switches means fewer points of failure in the network, more efficient use
of physical space in equipment offices and lower equipment costs, says
Arellano.
Indeed. By using Ascend Communications Inc.'s GX 550 Smart Core
ATM switch, which has an integrated SONET line card, service provider
Williams expects to save up to 85 percent on its network buildout costs,
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.
The company also expects to reap savings on the network maintenance
balance sheet.
"We're removing network elements so there are fewer points of failure.
We don't need special SONET and [digital cross-connect] guys," Price
says. "The ATM to optical interface is really happening."
Ascend and Williams, which last month launched a live field trial on the
Williams network between Washington and Atlanta, also are working
with dense WDM (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. Ascend's switch, for
example, allows the carrier to reconfigure private lines in a few minutes.
But Fujitsu's Eisenach says 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.
On the reliability side, SONET is designed to reroute traffic, in the event
of a fiber cut, within 50 milliseconds of the outage, says Eisenach. It
typically takes ATM switches between 300 and 500 milliseconds to do
that restoration, he says.
"ATM networks may not need SONET because ATM can monitor the
quality of the signal, but we also offer protection at the optical layer,"
says Roselyne Genin, vice president of optical networks and transport
solutions for Ericsson Inc.
ATM does some restoration in small networks, says Lucent's Szelag.
"If you took a bank's ATM network with a few sites, ATM could restore
it 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 enough."
To make IP interconnect to WDM without SONET a company would
need optical rings or optical cross-connects all over the place, plus the
company would need to improve IP for voice.
"If those two things happen, then you're ready," she says, adding that's a
few years off.
But Denny Bilter, director of marketing for Ciena, says SONET
capabilities can be integrated into equipment such as the WDWM gear
his company sells.
"SONET is really a redundant layer. It's not necessary," he says.
Survivability and muxing are key functions of SONET, he says, but Ciena
integrates those capabilities into its ATM WDWM and IP WDWM
products. At Supercomm '98, Ciena performed demonstrations both
with and without SONET, he says.
Companies with an embedded base on SONET might find that the most
attractive route, but newer carriers might find it overkill, Bilter and others
say.
"If routers are operating at OC-48 rates, it doesn't make sense to plug
them into SONET at OC-48, because they take up the entire bandwidth
on the ring. That's where WDM comes in," says Fraser of Cisco. "We
still use SONET framing. SONET framing lets you do operations and
maintenance functions. It tells you where the start of a frame is; the more
important part is it gives you bit errors on the link, isolates faults and sets
loop backs. If we do something else, we just need to build SONET all
over a again."
But nobody offers ring switching on ATM or IP yet.
"Theoretically you can do that," says Brian McFadden, general manager
of optical network applications at Northern Telecom Inc. "If you want to
build a uniform IP or ATM network and you can put ring switches on it,
fine, but in a multiprotocol network that's evolving, I think you'd want
SONET to put it on a survivable network."
WDM ultimately could be integrated into switches, adds McFadden. But
the more integration of products there is, he says, the tougher it is to
upgrade those products, because the upgrades affect every function of
that box.
Copyright c 1998 by Virgo Publishing, Inc.
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