techguide.com
That's your best source for technical papers. There's one for DWDM and for SONET.
And from Lucent's website, their paper on DWDM:
lucent.com
One other article from Inter@ctive Week:
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Shedding Light On Optical Networking
June 8, 1998
Optical Networking In The Future
By Fred Dawson
Contributing Editor
Technical breakthroughs supporting the rollout of this year's state-of-the-art optical networking products have set the stage for an evolution to much more advanced capabilities that are likely to emerge piecemeal in various niches of the operating sector before taking hold universally.
It might seem rather simple to make the transition from Dense Wave Division Multiplexing (DWDM) systems using new optical add-drop multiplexers (ADMs) to networks employing dynamically configured optical cross-connects and, eventually, optical switches. But the market conditions that would make such systems economically attractive to network operators remain uncertain.
The most significant drivers toward implementation of advanced optical networking at the regional level - that is, in places other than the long-haul stretches of long-distance networks - can be found in certain distribution network strategies within the Internet service provider, cable and local telephone company sectors.
Regional network penetration of DWDM is the key to pushing vendors to more advanced cross-connect and switching capabilities, says James Frodsham, director of high-capacity networks at Northern Telecom Inc.
"Implementing dynamic add-drop multiplexing is not a technical stretch from where we are with fixed add-drop capabilities," Frodsham says. "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, there have been few networking implementations of DWDM outside the long-haul stretches of long-distance networks. Companies deploying DWDM in a handful of metro rings include MCI Communications Corp., Teleport Communications Group Inc. and WorldCom Inc. At least one local exchange carrier, Bell Atlantic Corp., plans to do likewise.
However, several forces are at work, starting with finite-capacity limitations, that could push regional networks to DWDM faster than many people expect. Moreover, says Tim Krause, director of product marketing and business development at Alcatel Telecom'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 says. More important, he adds, the marketing of transport on a wavelength basis will let operators offer end users a way to enter the high-speed backbone in native formats, avoiding the costs of aggregating multiple service types.
"You can add a fast Ethernet link without having to choose between mapping it into something else or using separate facilities," Krause says.
Alcatel is moving quickly to a much larger cross-connect "that can be economically manufactured and readily available in the time frame the customer needs," says John Colbin, Alcatel's director of sales and services for AT&T Corp. 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 Synchronous Optical Network (SONET)-level applications that will be essential to more advanced systems, Colbin says.
But Alcatel won't be taking the next step to true cross-connect capabilities until next year. "To be a real cross-connect, it must be nonblocking, which none of the so-called optical cross-connects being introduced now can do," Krause says.
With the nonblocking capability, not only are the wavelengths routed or switched on the fly, but they are translated into other wavelengths to take advantage of available wavelength slots in a given fiber link as those slots open up in the ongoing routing process. Without 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 carriers can't live with in the high-volume environment of local telecommunications.
One company not waiting to move to this level of functionality is Tellium Inc., which is making its product debut at Supercomm '98 this week.
"The important thing to remember is that if you want a true all-optical backbone, you need the functionality that allows you to provision wavelengths dynamically as well as perform the monitoring and other tasks associated with traditional network architectures," Tellium Chief Executive Officer Farooque Mesiya says. "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 says the firm's 32-wavelength transport system is due in the second quarter and the first iteration of its cross-connect should come online by midsummer, with capacity expanding to 128 bidirectional ports by year's end.
GTE Internetworking is among the entities looking for the type of capabilities Mesiya talks 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]," says Steven Blumenthal, vice president and general manager of GTE Internetworking.
"Today we're deploying SONET multiplexers and also DWDM technology from Nortel," Blumenthal says. "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."
Another force driving optics on the distribution side and, by extension, the use of optical routing at the regional level is the use of fiber in the mass-market networks of the local exchange carriers and cable companies.
Cable, in particular, deploying a Hybrid Fiber-Coax (HFC) architecture that relies on fiber at the primary and secondary hub levels of the metro region, is now looking at DWDM as a way to maximize efficiencies of the embedded fiber infrastructure.
Tele-Communications Inc., for example, has decided to use DWDM to reduce electronics in its plant, with a single fiber carrying eight wavelengths from the headend to eight different hub distribution points. Each narrowcast - dedicated service - wavelength operating in the 1,550-nanometer lightwave "window" transmits up to 10 digitally modulated radio-frequency carriers from the headend to the hub, where each carrier is optically combined with broadcast cable services onto a 1,310- nanometer link to a node interfacing with a coaxial serving area. Thus, up to 10 nodes can be served by the narrowcast segments from a single wavelength.
This architecture vastly reduces the size of hubs and the cost of electronics, says Oleh Sniezko, vice president of engineering at TCI.
At least two vendors, Antec Corp. and Harmonic Lightwaves Inc., are moving to bring products to market that fit this architecture. "We've driven the development of this technology to where it is easily and cost-effectively deployable in large-scale systems," says Emmanuel Vella, vice president for optronics at Antec Network Technologies.
Telephone companies using HFC networks are looking at the new DWDM distribution system as well, says John Trail, product manager for transmission systems at Harmonic Lightwaves.
"BellSouth [Corp.] and Sprint [Corp.] are now conducting tests using our equipment in fiber-to-the-curb applications," Trail says.
Network operators are also looking at the ultimate in all-optical networking again, which is to say, fiber to the home. Lucent Technologies Inc., responding to growing demand in this arena, has embarked on product development in an initiative referred to by one researcher as "Quantum Leap."
"There certainly are some operators who are very serious about fiber to the home," says Tom Wood, a member of the technical staff at Bell Labs.
For DWDM systems like Lucent has in mind to be deployable in the distribution network, vendors will have to come up with low-cost waveguides that can be used at each node to siphon the wavelengths dedicated to the specific serving area. But the cost of such devices is dropping quickly, which is why Lucent and other vendors are offering metropolitan DWDM products, says Dave Schriftgiesser, director for broadband networking at Lucent's network systems unit.
Moreover, he adds, Lucent has now found a way to support a wide range of signal types in the conversion process at the node, greatly enhancing the flexibility of the DWDM setup.
"The key to being able to do DWDM cost-effectively in the distribution plant is the optical translator, which can handle any data format in the 150- to 750-megabit-per-second range," Schriftgiesser says. "Without it, you'd be running trucks every time the service profile changes."
With DWDM just beginning to migrate into the regional networks and some distribution networks, the market conditions are a long way from the point at which all-optical operations will become a reality. But clearly these trends and the more immediate force of IP-over-SONET will combine in the not-too-distant future to make it worth vendors' while to support the long-anticipated end-to-end optical network.
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