Does The ASND invention now permits ATM to be used directly with DWDM and eliminates the Sonet stage. If so, what are the implications for existing ATM switches.?
I'll let the following articles answer your questions since there's no straightforward answer.
<<<DWDM: The Long (Haul) and Short (Haul) of It
By Peter Meade
Dense wavelength division multiplexing (DWDM), already the darling of long distance carriers for its ability to efficiently add impressive capacity to their existing fiber optic networks, is becoming a growing attraction for the local loop.
Long- and short-haul carriers share a mutual interest in this technology because both are seeking remedies for fiber network congestion. DWDM systems are available today from such vendors as Alcatel Network Systems Inc., Cambrian Systems Corp., Ciena Corp., Fujitsu Network Communications Inc., Lucent Technologies Inc., Nortel and Pirelli. They have shown the technology can be used to multiply the capacity of an existing single optical fiber--which typically runs at 2.4 Gbps--by 16 times or more and support bandwidth of 40 Gbps or more in each direction over a fiber pair. Moreover, tomorrow's 40-channel systems promise 100 Gbps, the equivalent of 10 OC-192 transmitters.
"No one talked about bandwidth like this a year ago," says Pawan Jaggi, senior product planner, bandwidth transport planning for Richardson, Texas-based Fujitsu Network Com-munications. "And recent technological advancements have ensured the economic attractiveness of using DWDM, because it comes down to price in key enabling technology."
In addition to the growing demand for bandwidth, DWDM's increasing popularity can be attributed to two other factors: Prices for WDM components are dropping, and the technology continues to improve.
Mark Lutkowitz, president of Trans-Formation Inc., a Birmingham, Ala.-based market research house, says component prices have come down as much as 20 percent to 25 percent in the past six to eight months.
"Whatever has been done with an electrical signal can be done with optical, and it can be done cheaper at a higher level," says Tim Krause, senior director for business development and optical networks at Richardson, Texas-based Alcatel Network Systems Inc.
Time-division multiplexing (TDM) was commonplace when WDM first appeared in the 1980s. WDM started out in dual-channel wideband form, in 1310 nm or 1550 nm wavelength bands.
In the early 1990s systems emerged that could multiplex four to eight wavelengths, resulting in a notable gain in market momentum. The big gain came last year, when DWDM debuted, bringing with it network management capabilities and add-drop multiplexer functions. Now a selection of currently available WDM systems can handle eight to 16 wavelengths, which in many applications help interexchange carriers squeeze more capacity from their OC-48 (2.4 Gbps) backbones.
According to Trans-Formation Inc., the domestic market for WDM will grow from last year's $80 million to about $330 million by 2000.
The most common form of DWDM uses half of a fiber pair for transmission and half for reception. There also are systems in which a single fiber carries bi-directional traffic, but this approach reportedly sacrifices capacity and amplifier performance due to their configurations, according to several market players. In contrast to wideband WDM, also called interband or non-dense, all the optical carriers are within the same window and run within only a few nanometers of each other. Due to signal amplification traits of today's new optical amplifiers, this window is around 1550 nm.
This new brand of amplification, performed by erbium doped fiber amplifiers (EDFAs), can amplify all the wavelengths at the same time, helping DWDM systems achieve widespread commercial deployment. EDFAs differ from traditional regenerative or electro-optic repeaters in that the light does not require conversion to an electrical signal, amplification and then reconversion to light, explains Alcatel's Krause. EDFAs also can lengthen transmission distances to more than 300 km without regeneration, saving both time and money.
Long-haul carriers, such as AT&T, Bell Atlantic Corp., BellSouth, MCI Communications Corp., Sprint Corp. and WorldCom Inc., have invested heavily in the technology for long-haul applications. According to Kevin Slocum, managing director at Stamford, Conn.-based SoundView Financial Corp., Sprint is the most aggressive deployer of DWDM. "But we are just scratching the surface of fiber in the network," he adds. "The lower the cost, the closer the fiber will get to the home."
DWDM Components
North America ($millions) 1995$52.522000$1828.72005$5729
Worldwide ($ millions)1995$100.892000$174.12005$121.28Source: ElectroniCast Corp.
Fiber relief is the main requirement in designing for long haul, says Solomon Wong, director of product management for Ottawa-based Cambrian Systems, which--along with Linthicum, Md.-based Ciena Corp.--is leading the charge to the local loop. However, Wong notes, short-haul applications require systems that offer greater flexibility, scalability and operational ease.
Moreover, explosive Internet, intranet and extranet growth has changed the economic model for building these networks. For example, data traffic in the public switched network in the San Francisco Bay area doubles every 10 months, says Joachim Vobis, a Santa Rosa, Calif.-based product manager, optical spectrum analysis, at Hewlett-Packard. With that kind of growth, megabits become gigabits very quickly, he says. DWDM offers a promising solution.
DWDM systems, with network management gear and add-drop multiplexers, represent an attractive option because the cost of adding fiber to any network remains pricey, no matter who's talking. Costs for deploying fiber can exceed $70,000 per mile, according to several industry players. For this reason alone, as well as others--such as the limitations of current products and legacy installations--relieving fiber congestion by deploying more fiber is not always the best answer. This may be especially true for local traffic in highly congested areas, where additional fiber deployment can be extremely challenging or impossible. According to Douglas McKinley, director of engineering for Sprint's long distance division, the $70,000-per-mile price tag is "on the skinny side" of the price chart. "In the prairies, perhaps," he says. "But the sky's the limit in metropolitan areas, so we must eke every bit out of existing fiber." Jeff D. Montgomery, founder and chairman of ElectroniCast Corp., a San Mateo, Calif.-based research house, says prices may be as low as $10,000 per mile if suitable ductwork is available.
In some instances, short-haul DWDM systems actually can be simpler and less expensive to install because they do not require expensive optical amplification, says Alcatel's Krause. Moreover, simplicity, cost reduction and speed to market make short-haul DWDM applications increasingly attractive, says Cambrian Systems' Wong.
There does, however, remain the high cost of terminals, which may make some short-haul applications price-prohibitive. This is not the case when the cost of terminals is stretched over a long-haul application, explains Sprint's McKinley. In some cases, though, installing terminals remains cheaper than the cost of deploying more fiber, he says.
A universally acceptable answer is cheaper terminals. "We don't need sophisticated filters for the local loop," McKinley says. Yet his colleague Samuelson adds that some vendors remain firm in requiring them--a point of debate that may cost these vendors their share of the market.
Companies such as Cambrian Systems and Ciena, however, are delivering local boxes that do not include amplifiers, Samuelson says. If Cambrian's OPTera can handle up to 40 km, it is sufficient for 80 percent to 90 percent of Sprint's local loops, he adds.
The growing array of short-haul DWDM systems should be of particular interest to competitive local exchange carriers (CLECs) because of their ability to deliver new services more quickly while reducing the costs associated with delivery that, in turn, allow CLECs to offer services at a more attractive (and competitive) price. "Short-haul systems will change the way CLECs as well as incumbent local exchange carriers (ILECs) deploy bandwidth," says Cambrian Systems' Wong. For example, carriers now will be able to offer services on an individual wavelength basis.
But, even with all the positive momentum, DWDM in the local loop has a way to go, according to several market watchers. "Fiber is making its way from a long haul-only application to short haul," Leon says. "But it will be a long time before fiber-to-the-house is a mass reality."
Sprint currently is evaluating several 32-wavelength products and one 40-wavelength offering. Testing will begin in Sprint's lab in the fourth quarter, McKinley says.
According to ElectroniCast's Montgomery, Bell Laboratories is looking even further ahead. DWDM technology with wavelengths of 64, 72, even 100 are not inconceivable, he says. The widespread availability of these wares has become an economic --not a technological--issue, he adds.
And, Lucent reportedly has developed one laser that can replace 206 by using WDM to generate 206 separate wavelengths, each carrying 36.7 Mbps of data.
According to Alcatel's Krause, DWDM is just the beginning of tomorrow's photonic network, in which DWDM systems with open interfaces will give carriers the opportunity to deliver SONET, ATM, frame relay and other protocols on the same fiber. Achieving an open systems environment means additional costly, optical transmitters are not needed to interface with specific protocols. Instead, less expensive transmitters can do the job. "Bit-rate protocol independence gives flexibility and growth," says Cambrian Systems' Wong. "We can go from OC-3, to OC-12 to gigabit Ethernet without changing the network interface. Carriers may hate changes, but what they hate more is having to take their networks down for 16 hours for upgrades."
Sprint will be using WDM in 70 percent of its route miles by the end of this year, according to the company. And that figure is expected to surge to 98 percent by the end of year. McKinley clarifies the statistics by explaining that certain route miles already contain several WDM systems. Other route miles currently without may not carry enough traffic to be WDM-worthy. Regardless, "WDM will be ubiquitous in Sprint's network by next year," says McKinley, who predicts several of Sprint's competitors likewise will buy into WDM in a big way.
DWDM's growth from ubiquitous in the long haul to a familiar site in the local loop may slow the need for some new fiber deployment, but it is not likely to hurt the overall fiber game, says SoundView's Slocum. "After all, you cannot continue to leverage all the benefits of DWDM without having the access in the ground." >>>
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Shedding Light On Optical Networking<Picture>June 8, 1998
Optical Networking 101
By Carol Wilson
Optical networking has burst onto the telecommunications scene with hurricane force, blowing new bandwidth into exhausted fiber-optic cables.
The concepts behind optical networking - putting hundreds of new signals onto a single fiber-optic strand and amplifying their power using other specially treated strands of cable - can seem exotic and mysterious and sometimes can defy understanding.
The articles in this special supplement take a look at what optical networking is today, what it is becoming and what it will be in the future. Understanding what is written in these pages requires some basic knowledge of what optical networking is and how key elements are evolving.
At its most rudimentary, optical networking involves dealing with transmission signals as wavelengths or colors of light, rather than as electrical pulses. This is made possible by two recent technological advancements: the ongoing evolution of tunable lasers and the development of optical amplifiers.
Tunable lasers are simply light sources that can be fixed to transmit light in a very specific wavelength or color of light. The more precisely these lasers can be tuned, the more wavelengths can be packed onto a single fiber. This is because precision eliminates the need for spacing between wavelengths to prevent interference.
Optical amplifiers are pieces of fiber that are doped with erbium, an element that, engineers have discovered, can boost the power of an optical wavelength. In fact, it can boost the power of many different wavelengths, and it does so passively - that is, without electrical power or electronic systems.
A long-distance company can install Dense Wave Division Multiplexing (DWDM) equipment - the stuff that packs multiple wavelengths onto a single fiber - into its network and place optical amplifiers at the point of generation. This not only gains more bandwidth, but also eliminates the need to periodically regenerate the signal to boost its strength. Taking regenerators out of the network means eliminating maintenance and powering challenges, as well.
Optical networking only starts with DWDM, however. Coming onto the market this year are optical cross-connect systems, which direct optical signals without first converting them into electrical signals. This achieves other new efficiencies.
In today's transmission networks, the dominant means of managing bandwidth involves the Synchronous Optical Network (SONET) standard.
Using SONET, a network operator transmits signals as beams of light. At points in the network where traffic drops off or gets on, that beam of light is converted to an electrical signal so that traffic can be added or dropped. This is done at a SONET Add-Drop Multiplexer (ADM), which represents a leap forward from previous systems that required an entire high-speed payload not only to be converted from optical to electrical signals but also to be brought down to the lowest transmission speed.
As very high-speed signals begin to connect fast, powerful routers, however, it becomes inefficient to convert every optical signal to an electrical signal to drop off or add bandwidth. Thus, the industry is moving ahead to create new ways of managing bandwidth as colors of light for circumstances in which that would be more efficient.
Longer term, it is possible to envision the day when most of the networks are optical and the equipment we are familiar with today - switches, ADMs, cross-connects - are all equipped to handle signals as wavelengths.
Turning this page, you'll find out in greater detail how network operators are using what's available today in optical networking - and what they are hoping to get from vendors in the future.
Now that you've mastered the basics, it's time to move on to the advanced class.
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Optical Networking Tomorrow
By Carol Wilson <Picture>
The dizzying pace of change in the optical networking industry will be most visible this week in Atlanta, on the exhibit floor of Supercomm '98 at the World Congress Center. There, a burgeoning number of companies - including giants and start-ups - will capture attention with technology that has come onto the drawing board only within the past year and yet is already about to become commercial product.
Just a couple of years after Dense Wave Division Multiplexing (DWDM) burst onto the scene with systems that put eight wavelengths to 16 wavelengths onto a single fiber, multiple vendors will be showing 32-wavelength systems, and a few such as Ciena Corp. and Lucent Technologies Inc. will have the much denser 80- to 96-wavelength systems.
It's telling, in fact, that optical network vendors have to break some of the rules surrounding publicly announcing technology before it is commercially ready in order to stay abreast of this market. Whereas equipment makers are traditionally criticized for preannouncing their systems, technology is jumping from lab to market so quickly in optical networking that preannouncements are a virtual requirement.
As a result, this week's Supercomm '98 show will set reasonable expectations for what optical networking will produce over the next 18 months. Many of the products and systems being previewed at the show are expected to be available late this year or in early 1999 and will show up in live networks by midyear 1999.
The rapid progress of optical networking is being driven by demand: Carriers - initially the long-distance and new service providers but now also local telephone companies - see the bandwidth crunch that the boom in data traffic is causing and are asking for more bandwidth on each fiber-optic strand. The next step becomes obvious: providing the means to manage all that bandwidth in the most efficient way possible.
"Networks are going to scale to become very large even relative to what they are today," says Jack Wimmer, executive director of network and technology planning at MCI Communications Corp. "A phone call today consumes 64 kilobits per second of bandwidth, but the average 'data call' of tomorrow will consume 1 megabit or more. So we have to think about networks that scale even faster."
Creating scalable networks - those that can easily increase in size without having to remove or replace key components - means streamlining the optical network by doing as many functions as possible at the optical layer and eliminating the need for multiple optical-to-electrical conversions of signals.
"In today's network, we have SONET [Synchronous Optical Network] rings coming into a service node, and those signals go through a light-wave terminal and are converted from optical to electrical, then multiplexed down and put through a digital cross-connect," says Harry Bosco, president of Lucent. "This happens to all the traffic, even though 40 percent to 50 percent goes on to the next office."
That will change as early as this year, equipment vendors say. Due to be available from a range of vendors by late 1998 are optical add-drop multiplexers (ADMs) that can carry an optical signal into a service node and drop off traffic that needs to be routed to customers served by that node, while allowing other traffic to continue without being converted to an opto-electrical signal by a SONET terminal. Built into optical terminals from some vendors will be ring capabilities - either unidirectional path-switched or bidirectional line-switched - that let network operators automatically route signals around an equipment failure or fiber cut, much as SONET rings do today.
Also commercially available this year will be optical cross-connects, the light-wave version of the systems that allows lower-speed signals to be exchanged between higher-speed pipes at a central location and provides an access point for testing signal quality.
In addition, network operators can expect to see optical interfaces on high-speed data equipment, such as gigabit routers, on the market this year, and they can expect DWDM equipment that is specifically designed and priced for metropolitan area networks.
Because this technology is so new, however, there are still standards and interoperability issues to resolve, and there are some fairly wide variations in the approach equipment vendors are taking to optical networking. The opportunity exists for innovation, and a number of companies are poised to capitalize.
"I don't think the standards are going to lead the product, I think it's the other way around," says Steve Chaddick, vice president of product development at Ciena. "The products will come first and then will evolve to meet the standards."
Lucent kicked off 1998 by announcing its WaveStar Optical Line System that can put 80 different signals at up to 2.5 gigabits per second each onto a single fiber. AT&T Corp. has been lined up as the first customer of that system, due out in the fourth quarter. The WaveStar and Lucent's Bandwidth Manager are scheduled to be on display this week in Atlanta.
Also this week, Ciena is expected to announce a 96-wavelength Sentry DWDM system intended for long-distance networks. Most vendors will have 32-wavelength or 40-wavelength systems and agree they are working on pushing the capacity envelope.
"We're only limited by the lasers and what people are building today," Chaddick says. "There's no definable ceiling yet."
The big push behind these fatter optical pipes is the need to connect ever-faster data routers that carry largely Internet Protocol (IP) traffic. That's why some vendors will be demonstrating IP directly over optical networks, eliminating the use of both SONET and Asynchronous Transfer Mode (ATM) switches in intervening network layers.
Both Ciena and Alcatel Network Systems Inc. will have live demonstrations at Supercomm that show optical connections directly into Cisco Systems Inc. routers. Such connections become important for point-to-point links between routers on large data networks.
Northern Telecom Inc. has announced joint development with Avici Systems Inc. to create optical interfaces for that company's terabit router.
"Today, it's one of the fundamental questions - are we going to handle IP over ATM over SONET over an optical layer, or does it make more sense for some networks to go directly IP over the optical layer?" says Joe Bass, vice president and general manager of light-wave products at Alcatel. "Right now, the SONET layer is in there for survivability reasons - it's what restores traffic within milliseconds when something goes wrong."
Ciena will demonstrate path-switched ring technology on its Sentry system, says Mark Yin, technical marketing manager at the company. "One of the things we'll show at Supercomm is IP restoration, ATM restoration and optical restoration."
Fujitsu Network Communications also will show restoration capabilities, using optical add-drop multiplexing and optical cross-connect technology.
The company says it has an edge in developing acousto-optic tunable filters that can filter - or reflect - specific wavelengths within a fiber optic system, letting others pass. The filters are incorporated into Fujitsu's Flashwave Optical ADM system, which ultimately will be used to do bidirectional line-switched rings, says Pawaan Jaggi, manager of Fujitsu's optical networking group. The acousto-optic tunable filters can be adjusted using sound frequencies so that the ADM can route traffic dynamically.
"The system can drop any of the 32 channels carried at any node," Jaggi says. "It's a truly dynamic ATM."
Using filters to route wavelengths is also built into Nortel's ADM product line, which will be on display at Supercomm. The company will exhibit a fixed optical ADM, in which the filters reflect prespecified wavelengths or colors of light out of the fiber-optic cable at a specific service node.
Tellium Inc., a relatively new player that was spun off from Bellcore, will also show off restoration of services at the optical layer, using both unidirectional path-switched rings and bidirectional line-switched rings, in what Tellium President Farooque Mesiya calls "SONET-like" capabilities.
"We are taking most of the SONET principles and allowing them to happen at much higher line rates," says Mesiya.
One way of doing this is to read certain key bits of the messages normally sent in the SONET overhead - data communications channels used to send messages between different network elements and network management systems - such as loss of signal, but not process the entire overhead.
That's a process, known as slimming down SONET, that network operators can also expect to see over the next couple of years, according to Lucent's Bosco.
"We'll incorporate what's required for optical networks to achieve the level of reliability that SONET can provide, but not try to do the full SONET overhead," he says.
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