This week marks another incremental step forward in the
optical-networking capabilities offered by telecommunications-systems vendors, as the
market continues to sort out just how fast the evolution to much more advanced systems
will be.
At the annual Supercomm convention in Atlanta, leading
system vendors such as Lucent Technologies, Alcatel Telecom and Nortel will be touting new
add/drop multiplexers and other components associated with
dense-wavelength-division-multiplexing technology deployed by long-distance carriers.
But it appears that only one vendor, start-up Tellium Inc.,
will be going so far as to introduce the true optical cross-connects and other
capabilities that would be needed to support all-fiber backbones at the
metropolitan-regional level.
Fixed add/drop capabilities seem to be sufficient for
LDCs' current needs, simply because they "have limited connectivity with other
networks, so they aren't dropping a lot of traffic along the way," noted James
Frodsham, vice president of optical systems at Nortel.
The value proposition is harder to spot for use of
advanced-optical systems in regional networks, he added.
"Implementing dynamic add/drop multiplexing is not a
technical stretch from where we are with fixed add/drop capabilities," Frodsham said.
"All-optical networking is a sexy concept, but the question is: What's the
utility? We're working with a number of customers to figure out the value
proposition."
So far, regional-networking implementations of DWDM have
been few and far between. Companies deploying DWDM in a handful of metro rings include MCI
Communications Corp., Teleport Communications Group and WorldCom. And at least one
local-exchange carrier, Bell Atlantic Corp., is preparing to do likewise.
However, several forces are at work, starting with finite
capacity limitations, which could push regional networks to DWDM faster than many people
expect.
Moreover, said Tim Krause, director of product marketing
and business development for Alcatel's lightwave-products unit, deregulation has
engendered a new business approach among incumbent carriers where flexible allocation of
capacity to multiple network providers is vital to success.
With implementation of DWDM and advanced-optical routing,
owners of fiber links will be able to sell "fractional dark fiber," using some
wavelengths for themselves and wholesaling others, Krause said. More important, he added,
the marketing of transport on a wavelength basis will allow operators to offer end-users a
way to enter the high-speed backbone in native formats, avoiding the costs of aggregating
multiple service types together.
"You can add a fast Ethernet link without having to
choose between mapping it into something else or using separate facilities," Krause
said.
Such capabilities are not what Alcatel, Nortel and most
other vendors introducing optical add/drop multiplexers have in mind right now. In
Alcatel's case, a new 128-by-128 OC-48-gateway cross-connect is seen as an answer to
long-haul carriers' needs to maximize the efficiency of DWDM capabilities, said Paul
Baniewicz, the vendor's product manager for core transport network.
AT&T Corp. has agreed to test and deploy the Alcatel
gateway, which has many of the features that will eventually support dynamically
assignable, "on-the-fly" routing across the optical-wave guides, Baniewicz said.
"We see the optical-gateway cross-connect as a
migration path to full-wavelength switching," he said, noting that the new system can
support four bidirectional fiber rings operating at a rate of 10 OC-48s, or the equivalent
of OC-192 (10 megabits per second), per fiber.
Alcatel is moving quickly to a 512-by-512 fabric "that
can be economically manufactured and readily available in the time frame that the customer
needs," said John Colbin, Alcatel's director of sales and services for AT&T
core-network applications.
The migration path to dynamic switching is made possible
because the initial optical-gateway product supplies the optical restoration and
management for SONET-level (synchronous optical network) applications that will be
essential to more advanced systems, Colbin said.
But Alcatel won't be taking the next step to true
cross-connect capabilities until next year, Krause said.
"To be a real cross-connect, it must be
nonblocking," he added.
With the nonblocking capability, not only are the
wavelengths routed or switched on the fly, but they are translated into other wavelengths
in order to take advantage of available wavelength slots in a given fiber link as those
slots open up in the ongoing routing process.
Minus this capability -- which must be accomplished without
converting the signal to electronic frequencies and then regenerating it -- a switched
wavelength will be blocked until its slot opens over a desired link, which is something
that carriers can't live with in the high-volume trafficking environment of local
telecommunications.
One company that is not waiting to move to this level of
functionality is Tellium, which is backed by SAIC Inc., laser supplier Ortel Corp. and
several investment firms, and which is making its product debut at Supercomm.
Tellium is acting now to bring next-generation capabilities
to market because there's a significant value proposition to be found in all-optical
trafficking where the regional handoff is to optical links in the distribution network,
said Tellium CEO Farooque Mesiya.
"There are an increasing number of networking
environments at the regional level where optical interfaces to the distribution level make
a lot of sense," Mesiya said.
"Our view is that in the all-optical domain, SONET
migrates to the edge of the network, because you have dynamic control of multiplexed
signals at the core. If you have a data router that is putting out a multiplexed signal at
OC-48, you don't need to run it through a SONET multiplexer if you're operating
over a purely optical network," he added.
Mesiya said the firm's 32-wavelength transport system
is available now, and the first iteration of its cross-connect will come online by
midsummer, with capacity expanding to 128 bidirectional ports by year's end.
The products support remote, dynamic provisioning of
wavelengths; monitoring of the bit-error rate and other performance elements; and
restoring of the traffic at a high level of grooming in the central office, without
requiring that the signal be broken down and reconstituted, he said.
GTE Corp.'s GTE Internetworking unit is among the
entities looking for the type of capabilities that Mesiya is talking about -- using SONET
as the edge interface with routers in what has become known as "IP [Internet
protocol] over SONET" configurations.
"Aside from using [IP over SONET as] a point-to-point
connection between routers across our wide-area network, we're also looking at it as
an interconnecting mechanism within our POPs [points of presence]," said Steven
Blumenthal, vice president and general manager of GTE Internetworking.
"Today, we're deploying SONET multiplexers and,
also, DWDM technology from Nortel," Blumenthal said. "Going forward, we're
hoping to be able to avoid some of that SONET-muxing technology and to be able to have the
routers plug directly into the optical layer. That's something that we see coming
that will be of real benefit to us."
Such capabilities add up to "a new world network based
on data services," said Graeme Fraser, vice president of marketing at Cisco Systems
Inc. There will be rapid evolution of IP-over-SONET from today's point-to-point
capabilities, first to ring architectures, and "then to more complex mesh topologies,
as it plays into layer-three routing," he said. "You'll see routers and IP
move much closer to the physical layer and be part of a core infrastructure that very
efficiently maps variable-length packets across optical technologies."
