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December 1, 1999
By Khali Henderson
The New Wave in Leasing Fiber
By Khali Henderson and Charlotte Wolter
In "telecom-speak" lambdas are not fraternity members, but their availability
on a wholesale basis is expected to be offered by a growing club of carrier’s carriers.
Lambdas are basically discrete wavelengths of light that traverse a fiber optic network
and, for wholesalers, bridge the gap between dark fiber and private lines, say advocates.
The addition of colors, or wavelengths, is made possible by dense wave division
multiplexing (DWDM) equipment that has been on the market for some time. Its recent
emergence as a service delivery medium–and a new unit of commerce for service
providers–is attributable to advances in optical network management. It also may get a
boost from just-announced advancements, enabling service providers to instantly direct and
route optical signals from fiber to fiber in the network without first converting them to
electrical form as done today.
"Service providers will move from leasing dark fiber, the physical medium, to
leasing lightpaths, an end-to-end optical path through the network," explains
Sycamore Networks, Chelmsford, Mass., in its primer on intelligent optical networking.
"Services are mapped directly onto the lightpaths without any intervening
transmission equipment, enabling service providers to quickly add new services or increase
bandwidth without impacting existing traffic."
Announced in June and made available in October, Williams Communications Group Inc.,
Tulsa, Okla., is the first carrier’s carrier to tender such an offer publicly. Called
Optical Wave Service, Williams’ offer enables wholesale customers to lease individual
wavelengths providing "clear" channel OC-48c capacity on Williams’ nationwide
fiber optic network. To provide its service, Williams is deploying an intelligent
wavelength DWDM conversion and management system from Sycamore Networks that interleaves
OC-48c optical channels with its existing OC-192 optical channels. This system is expected
to be deployed throughout the company’s network by the fourth quarter.
The service provides a transparent interface with a customer’s network for completion
of synchronous optical network (SONET) rings, construction of diverse or required routes
and transmission of asynchronous transfer mode (ATM) or Internet protocol (IP) traffic.
"The first users of lightpath services are likely to be service providers
themselves who purchase backbone bandwidth at speeds of OC-48/STM-16 and above to complete
their data networks," states Sycamore Networks in its primer. "As time goes on
and intelligent optical networking technology spreads throughout the network, optical
services will find their way to the enterprise user and will provide the foundation for
very high-speed optical extranets to support an e-commerce-based economy."
DWDM is a key technology in long-haul networks, because it gives carriers the ability
to multiply the capacity of fibers by factors of 16, 32 and even 80 in the most advanced
systems. It does this by sending multiple colors or wavelengths of light down a fiber,
rather than just one color.
The signals at each color or wavelength are generated by a separate laser in the DWDM
transmitter/receivers, so these pieces of equipment can be quite expensive. However,
service providers can start with as few as four wavelengths in a chassis and add
additional cards later as demand grows.
The different wavelengths are all grouped around 1550 nanometers, the most widely used
frequency in long-haul optical networking today. The colors are kept separate by very
sophisticated diffraction gratings (which act something like a prism). Waves can be added
or dropped at nodes with the use of highly developed filters. The cost of a DWDM system is
influenced by how finely it can differentiate among waves (which determines how many waves
it can transmit) and how precisely it can add and drop them at nodes.
DWDM has precipitated changes and new opportunities in the dark fiber business. By
adding DWDM equipment, these service providers gain additional capacity and have the
option of leasing individual wavelengths rather than a whole fiber. Each wavelength could
be leased to a different customer, because although the waves are all on the same fiber,
they operate independently. Each wavelength can carry the same capacity as a whole strand
of fiber, such as a SONET multiplex, e.g. OC-12 (622 megabits per second) or OC-48 (2.5
gigabits per second). To the customers, it appears as if they have their own leased
An additional alternative that some dark fiber operators are exploring is leasing a
wavelength with a managed service on top of it. For example, MetroMedia Fiber Network,
White Plains, N.Y., is offering waves with equipment that transmits Ethernet natively
(without SONET equipment, which adds cost). The customer "owns" a pipe that
today has the capacity of carrying gigabit Ethernet, but does not have to pay for that
full capacity until it is used. If a terabit Ethernet technology should become available
in the future, the customer does not pay more for the pipe itself, just for the
transmission equipment at either end.
The concept of leasing wavelengths and running a network based completely on
wavelengths has been given even greater potency by the announcement on Nov. 9 of an
optical switch, the WaveStar LambdaRouter, by Lucent Technologies Inc., Murray Hill, N.J.
There are large wavelength-based optical networks today, such as Williams’. However,
these networks have no way to switch wavelengths as light. They must convert the signals
to electricity, switch them in huge digital cross-connects by companies such as Tellium
Inc., Edison, N.J., then convert the signals back to light and send them on their way. The
digital cross-connects are able to switch large numbers of waves–matrices of 256 by 256
now are available–and huge bandwidths, but at some point it will be difficult for the
processing power of the chips that do the switching to keep up with the volume.
By contrast, the true optical cross-connect of the LambdaRouter is simplicity itself.
Waves are switched by bouncing them off tiny mirrors no bigger in diameter than a human
hair. The angle of the mylar-like mirrors is changed by small changes in heat. The whole
256-by-256 cross-connect is less than an inch across. Theoretically, it can switch many
times the capacity of all-optical networks today.
Maintaining all-optical traffic paves the way for network providers to offer customers
instant Internet and other high-speed data and video services as well as to sell and
manage bandwidth as individual optical wavelengths, Lucent states in its launch release.
For example, a provider could initiate a videoconference at a moment’s notice. The same
task, without the all-optical link, would require the carrier to patch together a series
of digital switches, which would take several hours and considerably more network and
The other important characteristic of wavelength-based networks, whether they use
electrical or optical cross-connects, is their ability to manage these networks end to end
using technology that is often referred to as intelligent optical networking. Sycamore
Networks has the Silvx Optical Network Management System that allows service providers to
provision wavelengths in the optical network, scale the network rapidly, monitor
performance, and assess and respond to requirements for additional capacity.
This kind of capability allows service providers to turn up services very quickly in
DWDM networks. It also allows them to manage networks that may have very complex mesh,
rather than ring, architectures. Without the ability to look at the network end to end,
the multiple wavelengths could look as complex as a plate of spaghetti.
Traditional vs. Intelligent Optical Networks
Traditional SONET/SDH Network Architecture
Intelligent Optical Network
Unit of commerce
A strand of fiber
An optical length
Up to 50 percent reserved for protection
100 percent available
Linear, rings and mesh
Provisioning time for high-speed services
Days (moving over time to hours, minutes and eventually to
End-to-end network management
Entire network affected
Insert only where needed – "slide in a card"
End to end – "point, click, done"
Class of service
Protected, unprotected, pre-emptable
Source: Sycamore Networks, Chelmsford, Mass.
Khali Henderson is editor-in-chief and Charlotte Wolter is infrastructure editor for
Read more about:Agents
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