Multiple vendors confirm OSI Sonet interoperability

Nov. 1, 1996

Multiple vendors confirm OSI Sonet interoperability

george kotelly

Representing the next step in achieving multiple-vendor equipment interoperability (see Lightwave, August 1995, page 1), Bell Communications Research (Bellcore) in Morristown, NJ; Fujitsu Network Communications Inc. in Richardson, TX; and Lucent Technologies in Murray Hill, NJ, conducted the first public demonstration of full seven-layer, open systems interconnection (OSI), Synchronous Optical Network (Sonet) operations communications interoperability. The demonstration took place in the Bellcore booth at the 1996 National Fiber Optic Engineers Conference held recently in Denver.

Bellcore supplied its licensable ocat protocol test software, Fujitsu provided its FLM 600 ADM Sonet add/drop multiplexer, and Lucent furnished its DDM-2000 OC-3 Sonet multiplexer. Two Sonet analyzers (AP-9460B) and one protocol analyzer (AE-5150S)) from Ando Corp. in Rockville, MD, were used to check out network operation.

The point-to-point network consisted of approximately 15 m of singlemode fiber-optic cable and operated at 155-Mbit/sec OC-3 rates at 1310 nm (see figure). This test demonstration corroborated that true Sonet interoperability was accomplished in accordance with standards specified by the Sonet Interoperability Forum (SIF), Bellcore and the American National Standards Institute.

Explains Simon Leopold, Bellcore principal project manager, professional services, "This exhibit demonstrated the ability to remotely log onto another supplier`s network element. For example, it typifies how a network operator in a central office containing the Fujitsu multiplexer could use network input commands and remotely log onto the Lucent multiplexer in another central office miles away, and vice versa.

"The interoperability milestone is that to establish network connections, interaction took place at each of the seven OSI layers. These layers determine addressing, connections and validity of the traffic. But even this simple demonstration needed a series of difficult protocols and steps to make it all work."

For the demonstration, all the companies worked together to implement successful seven-layer OSI stacks, including the target identifier address resolution protocol (tarp) and transaction language (TL1) applications. Their cooperation highlights the benefits of developing products to industry standards, identifying opportunities to improve standards and emphasizing the potential of Sonet network capabilities.

"Sonet standards that exist today support interoperability, but they do not guarantee it," says John Palladino, Sonet interoperability project manager at Bellcore. "Different suppliers` equipment can pass conformance tests and still not interoperate."

Lynn Erb, Lucent Technologies product manager of DDM-2000 multiplexers, says, "We see our customer base trying to include more than one vendor`s solution in their networks, as opposed to being tied to one vendor. In addition, we are getting good directions from SIF, which is pushing all the vendors to align on a specific interoperability direction. By having a common direction and a third party such as Bellcore making recommendations, all vendors can align to a standard interface. An independent or third-party agency serves best when you have competitors in the same equipment arena.

"We welcome other vendors to come forward for more Bellcore testing. This point-to-point network demonstration is step one, but we need to get to more typical customer topologies, such as ring topologies. Interestingly, we had interoperability working in less than a week with Bellcore assistance," says Erb.

"As a leader in implementing and defining Sonet protocols, Fujitsu donated example source code for the tarp protocol to SIF members in 1994 and the ftam [file transfer access and management] profile in 1995," states Ron Martin, senior vice president of planning and development at Fujitsu. "In addition, Fujitsu`s Sonet products have undergone extensive testing both internally and by Bellcore to ensure conformance to operations and performance standards."

Network benefits

Proper communications messages as delivered over the demonstrated Sonet network would enable network providers, such as telephone and cable-TV companies, to verify that the information is being successfully transmitted between network elements. In commercial Sonet networks, network planners and providers prefer to mix and match crossconnect, add/drop multiplexer and digital-loop carrier equipment from different suppliers. These multiple-vendor devices, however, need to work together to receive, process and deliver network-level information.

According to Leopold, "For network providers, the Telecommunications Act of 1996 introduces a new way to look at interoperability. In the past, interoperability and the opportunity to deploy communications networks were viewed as luxury issues. That is, network providers could opt to purchase equipment from two or three suppliers and select different equipment from different vendors as desired. With tele com munications reform and interconnect unbundling, networks are now required to interface to other networks.

"In fact, unbundling is going to take place in all three network areas--transport, switching and access. Consequently, network providers have less control over whose equipment and what networks they are going to be able to interconnect. The result is a shift from a luxury status to a necessity status. Network providers now have a mandate to move to equipment and network interoperability."

Centralizing management and control

Using the Sonet data communications channel (DCC) to transport operations communications information lets network providers centralize total management and control of Sonet networks. Presently, telephone carriers get around the interoperability issue by deploying single-equipment-supplier networks or by installing complicated, extended overlay networks to maintain and control their networks.

Palladino says, "Networks are evolving into single-supplier islands and, most likely, are not using the DCC. This channel enables the concentration of network control from a single location for administrative purposes. Separate islands of control result in equipment interface and connectivity interoperability and communications issues."

The Bellcore portfolio of protocol analysis tools provides test suites that can check out the upper layer protocols--common management information protocol, remote operations service element, ftam and TL1--with the embedded OSI Session and Presentation layers. In addition, an OSI management test system from German supplier Danet GmbH operates with Bellcore`s ocat software on the Ando AE-5150S protocol analyzer. Armed with this software, this analyzer queries the OSI seven-layer protocol stack layer by layer--each layer has its own responsibilities for communications, routing and tracking tasks--and interrogates the network`s DCC for Sonet interoperability.

Chip Current, Bellcore member of technical staff, network operations analysis, says, "The demonstration covered the full seven-layer OSI operation all the way to the TL1 application. The ocat tool monitored and certified that at every single layer from physical through application, connections and exchanges were occurring at every layer and providing a translation of each communications event."

In the demonstration, the two Ando AP-9460B Sonet analyzers were used to separate the two network nodes via optical splitters. The analyzers monitored, processed and dropped out the information being passed between the add/drop multiplexers. They then extracted the protocol stacks and transferred the operations messaging information via a V.11 interface to the Ando AE-5150S protocol analyzer for analysis. In this setup, they monitored, analyzed and displayed information for compliance to Bellcore GR-253-core, Synchronous Optical Network Transport Systems: Common Generic Criteria.

The next step

Bellcore`s Simon points out, "A public demonstration of common management information service element (cmise) and file transfers would be the next logical steps to full Sonet interoperability.

Palladino says that "true interoperability will happen when the management facility, ftam and cmise are fully interoperable among all network elements and all network management systems."

Sonet network equipment suppliers do not perceive an urgent need for interoperability. They, therefore, need a strong driving force. The open-competition ramifications of the Telecommunications Act and the open cooperation shown by the companies involved in the demonstration may be that force. q

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