'Breakthrough technologies' to make MONET fully optical network

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The multiwavelength optical-networking (MONET) consortium is putting the finishing touches on an experimental research network in Washington, DC, that links six government agencies. The latest upgrade provides what the consortium describes as "breakthrough technologies" that add flexibility, expand the transmission capacity, and transform the network from a point-to-point optical system to a fully optical network.

The Advanced Technology Demonstration network, or ATDnet, can carry a mixture of telecommunications traffic, including voice, data, and high-definition television (HDTV), simultaneously on various wavelengths. The ATDnet consists of two eight-wavelength rings, each connecting three agencies (see Figure). The east ring interconnects the Naval Research Laboratory (NRL), National Security Agency (NSA), and National Aeronautics and Space Administration (NASA) with equipment provided by Lucent Technologies (Murray Hill, NJ).

On the east ring, the Defense Advanced Research Projects Agency (DARPA), Defense Information Agency (DIA), and Defense Information Systems Agency (DISA) are connected with equipment provided by Tellium Inc. of Oceanport, NJ. At press time, the east and west rings were scheduled for interconnection through wavelength-selective crossconnects at NSA and NRL, offering a research platform for exploring the operation and behavior of complex optical networks.

The east ring of the ATDnet is capable of carrying the network's former full load of Synchronous Optical Network (SONET) traffic across a wavelength at OC-48 (2.5 Gbits/sec) speed. At the same time, the network can transmit various types and rates of traffic between different locations, such as Asynchronous Transfer Mode (ATM) at OC-48 and HDTV links at 1.5 Gbits/sec.

MONET is a five-year program that began in December 1994 to define and demonstrate how best to achieve multiwavelength optical networking on a national scale to serve commercial and U.S. government applications. The program, funded in part by DARPA for $5 million over a five-year period, sought to integrate network architecture, advanced technology, network management, and business drivers to achieve high-capacity, high-performance, cost-effective, reliable, transparent multiwavelength optical networking. Consortium members include AT&T, Bell Atlantic, BellSouth, Lucent Technologies, SBC Communications, and Telcordia Technologies, in cooperation with the NSA and NRL.

The MONET project first made headlines in 1997 with the progress it made in its New Jersey network, which consisted of three interconnected testbeds. The local-exchange carrier (LEC) testbed at Red Bank, NJ, incorporated four managed-network elements for multiple architectures, including multiwavelength two- and four-fiber ring topologies. This testbed demonstrated transparent multiwavelength operation, including digital video teleconferencing, cable-TV analog signal distribution, and multichannel 2.5-Gbit/sec transmission. The long-distance testbed at Holmdel, NJ, accomplished more than 2000-km transmission with dispersion management at 2.5 Gbits/sec. Also in Holmdel, the crossconnect testbed demonstrated a non blocking, eight-wavelength, 4x4 multiwavelength optical-network element using lithium niobate switching elements. This was a milestone in the development of multiwavelength technology toward commercialization.

"Following the New Jersey network operations, we redirected the program to construct the Washington, DC, testbed," says Nattu Srinivasan, technical director for advanced optical networking at Bell Labs, the research and development arm of Lucent. "The MONET technologies are a continuation of the ATDnet technology that already exists in the Washington, DC, area. Here, we're using these advanced network elements or prototype technologies."Th Acf148

The MONET project in Washington, DC, used the existing Advanced Technology Demonstration Network (ATDnet) linking six government agencies as a testbed for experimenting with prototype optical-networking elements. (Source: Bell Labs Technical Journal.)

The ATDnet became the testbed for MONET's prototype network elements for the last few years, using the latest technologies to achieve the objectives set forth by the consortium. "There are a number of key technologies and realizations that have gone on in MONET," says Srinivasan. "Some have to do with constructing the network elements and system aspects, and others have to do with management aspects. I think that, over time, these technologies will improve the performance and flexibility of the network, eventually making it into real products for the market."

The MONET wavelength-division multiplexing (WDM) network element provided by Lucent demonstrates how to increase the flexibility of commercial WDM systems. Originally targeted at long-distance point-to-point topologies to alleviate the problem of fiber exhaust, WDM is moving toward the metropolitan and enterprise markets as prices decrease. These areas require flexibility in assigning wavelengths. For instance, where current commercial WDM systems tend to have rather rigid rules in wavelength assignment, MONET's WDM network element can adapt incoming wavelengths at various bit rates up to OC-48 to any of the eight MONET-compliant wavelengths going out. MONET's WDM wavelength routing operation can route incoming wavelengths to any wavelength on any output port.

"The various aspects we've talked about over the last five years--how the optical layer offers flexibility in terms of transporting signals and its ability to carry ATM and SONET signals without the optical-to-electrical conversion at the optical layer--have come together," says Srinivasan. "It's exciting to see it coming to fruition. It's existing proof that we can experimentally understand various aspects of the optical layer."

The MONET consortium defined five pillars by which to measure its success during the program: massive aggregate capacity, reconfigurability, transparency, scalability, and interoperability. Massive aggregate capacity is the ability to enhance the use of available bandwidth on the fiber. The latest announcement of simultaneous transmission of several traffic types and bit rates over the same network seem to indicate success in increasing bandwidth usage. The other four pillars have been addressed as well, from New Jersey to Washington, DC.

"The level of transparency was demonstrated by the east ring accomplishments," says Srinivasan, referring to the ability to transport different protocols, different bit rates, and both digital and analog signals on any given wavelength without provisioning the network element to know what it is transporting. "Scalability was demonstrated in the New Jersey testbed, including the long-distance and crossconnect testbeds. It was further supported in the Washington, DC, area with the interconnection of six agencies with 2.5-Gbit/sec signals being transported. Configurability is fully built in, meaning once a signal enters on a particular wavelength, we can route that wavelength to any drop point in any node. In many cases, that flexibility won't be commercially available for some time."

Lastly, interoperability is demonstrated by MONET's use of different vendors whose products are interconnected on the transmission layer of the network, coupled with the ability to support similar minimal feature sets.

"I think I'd look at three different thrusts to categorize our level of success," says Srinivasan. "One is in advancing optical technologies and accelerating the ability to provide very large bandwidth. Secondly, the optical layer was once a vision which now, thanks to MONET, is at the implementation phase. Finally, MONET has provided a significant understanding of networking using the optical layer and helping us understand its capabilities."

Following the interconnection of the east and west rings, the MONET consortium will reach the end of its agreement, around the end of October. However, the tech nology developed by MONET is planned for use by the agencies beyond that time.

Although there is a commitment to the consortium, Srinivasan says the information gathered throughout the project is planned for release, as long as it doesn't infringe on any patents. The consortium's intent is to publish the information to the extent that it benefits the telecommunications industry.

"MONET is an outstanding example of how the government could set directions jointly with industry partners to advance networking capabilities and bring new technology to the user faster than would otherwise be feasible," says Srinivasan. "I think that working as a consortium has demonstrated an outstanding example of how to make these things happen."

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