Sonet conformance testing points to interoperability

Sonet conformance testing points to interoperability


In response to the industry challenge issued at last year`s National Fiber Optic Engineers Conference to deliver synchronous optical network interoperability, three companies--Fujitsu Network Transmission Systems Inc. of Richardson, TX, Ando Corp. of Rockville, MD, and Bell Communications Research of Morristown, NJ--combined their resources to demonstrate at this year`s conference the first public test of open systems interconnection protocols specified by the Synchronous Optical Network Interoperability Forum and Bellcore.

For its part, network equipment supplier Fujitsu built and operated a three-node, Sonet bidirectional ring network using its off-the-shelf FLM 150 add/drop multiplexers to transmit at an optical carrier, level three (155-megabit-per-second) rate. Operating at 1310 nanometers, the multiplexers transported the company`s OSI seven-layer protocol stack capabilities over data communications channels and an Ethernet link. The network used approximately 15 meters of singlemode, single-strand fiber-optic cable.

Contributing network test equipment, Ando connected three of its AP-946B Sonet analyzers to separate network node links via optical splitters. These analyzers monitored, processed and dropped out the information being passed among the add/drop multiplexers in the data communications channels. They extracted the protocol stacks and transferred the Sonet ring`s operations messaging information to an Ando AE-5150 protocol analyzer workstation for analysis. Also connected to this workstation was the Ethernet or local communications network link from one of the multiplexers.

In its network testing role, Bellcore installed its Ocat data analysis software tool on the Ando AE-5150 workstation. Based on criteria established by the Forum and Bellcore, the software tool analyzed the OSI seven-layer protocol stack, layer by layer, and checked the capability of the network`s data communications channels to ensure Sonet conformance.

The successful messaging delivered over the Sonet optical fiber network means that telephone and cable-TV companies will be able to confirm that the information related to operations, administration, maintenance and provisioning is being communicated from one network element to another. In addition, message communications capabilities were also delivered through the local communications network link.

Says Ron Martin, Fujitsu senior vice president for research and planning, "The only way to see if a vendor has met Sonet Interoperability Forum specifications is in a network with multiple network elements. By initiating pre-defined messages in the Sonet ring and monitoring them as they travel between the optical rings, Bellcore can get an accurate representation of [Fujitsu`s] data communications channel capabilities. Service providers, in turn, will have assurance that Fujitsu`s equipment can send and receive operations messages through optical links or electrical local area network connections."

Adds Bill Erickson, Fujitsu`s director of access planning, "With vendors building to the OSI protocols and submitting their products to test-vendors such as Bellcore for conformance testing, data communications channel interoperability will be achievable this year. Previously, each vendor implemented proprietary data communications channel protocols, which made interoperability impossible."

Sid Shelton, Bellcore`s executive director of Sonet technology, comments, "Bellcore is ready to share its [data analysis] software with the telecommunications industry as it moves forward with extensive deployment of Sonet transport systems and operations capabilities. We anticipate that network equipment manufacturers and network providers will want to accelerate delivery of interoperable communications among Sonet network elements and operations systems at minimum overall costs."

Key test

In Sonet deployments thus far, a key test of network operations has been missing--the interoperability of data communications channels. Fujitsu is presently developing OSI protocols and exploring conformance testing by taking the first step of achieving DCC interoperability. The company is opening up its specifications and going through formal public testing to ensure the meeting of specifications. If other Sonet equipment vendors do the same, then DCC interoperability will be completed for the network providers.

According to Erickson, "The OSI protocols are very complex. In the past, it has been easier for vendors to offer proprietary equipment and protocols to provide the functionality that customers needed, such as remote provisioning and surveillance. But with agreement on the OSI specifications, different vendors can develop products that meet these specifications and begin the Sonet interoperability process."

At the NFOEC `95 demonstration, the OSI protocol stack rode on top of the DCC. The stack information also came out of the Sonet network over a LAN interface, which in Sonet terms is known as a local communications network. Therefore, to accomplish Sonet conformance testing, the DCC and local communications network interfaces were checked.

According to Mike Griffin, general manager at Ando Corp., "These two interfaces covered two of the three DCC access points in a telecommunications system. The third or missing connection was an X.25 connection to an operating system. The decision was made by the involved companies not to demonstrate this connection or have an operating system on site; however, that connection could have been made."

States Erickson, "Fujitsu believes that conformance testing is necessary because of the large number of players in the Sonet industry. It`s not practical for one equipment company to do pair-wise interoperability testing with every other vendor. Conformance testing accomplished through a testing agency, such as Bellcore, is the best approach."

During the NFOEC demonstration, the Bellcore software separated each of the seven OSI layers. The software checked that each layer conformed to the actual protocol specifications and worked properly on a Sonet ring network. The SIF test suites delineated how the measurements were to be implemented and determined whether incompatibilities existed among the equipment.

Consequently, the demonstration established the groundwork to perform Sonet interoperability testing. Fujitsu implemented its OSI/DCC protocols; Bellcore provided the software for analyzing the Sonet/synchronous digital hierarchy protocols; and Ando supplied the test equipment that offered protocol access to multiple subnetworks.

In a Sonet network, providers and users want to mix and match equipment. For example, they might prefer to hook up a crossconnect device from one vendor, an add/drop multiplexer from another vendor and a digital loop carrier from yet another vendor. These multiple-vendor devices need to interoperate at a certain network level. The industry has already done that for the traffic mid-span meet by connecting equipment, transporting digital signal, level one and DS-3 signals and demonstrating protection switching. The next step is DCC interoperability so that the operations systems can communicate through a multi-vendor network. In that regard, says Erickson, "At NFOEC `96, Fujitsu would like to demonstrate a multi-vendor DCC mid-span meet."

Conformance testing

As proposed by Bellcore to the industry in general and to the telephone operators, in particular, Sonet provides a means of implementing multi-vendor, non-proprietary, interoperable transport mechanisms.

The NFOEC demonstration showed that a concerned industry vendor--Fujitsu-- came forward and confronted the technical issues dealing with the Sonet requirements for the conformance testing of the DCCs. These DCC tests are regarded by the industry as the first tests of interoperability. This strategic marketing move by Fujitsu was most likely in response to both competitive and operator pressures.

According to Griffin, "The significance of this demonstration is that Fujitsu took the risk and put the bulk of the funding into addressing the interoperability issue. The original promise of Sonet is being overworked, but has not yet been fulfilled. A solid interoperable network is needed regardless of the provider or operator to make a Sonet network work on a universal basis."

The promise of Sonet cannot be fulfilled without standardization and conformance testing leading to network interoperability. Without interoperability, the whole concept of multi-vendor Sonet rings is unworkable. For many years, network operators, private network owners and end users have emphatically expressed the need for bandwidth-on-demand.

Explains Griffin, "The next step is get other equipment vendors to move up to the mark set by Fujitsu and address the conformance issue first, and then move forward to interoperability testing. Otherwise, adding different vendor equipment could crash the network."

Test software

The Ocat operations test software designed by Bellcore can check out all the network elements involved--whether provided by a service provider, a network element supplier or an operations systems supplier. According to Simon Leopold, Bellcore senior product manager, broadband professional services, this relatively mature software is aimed at Sonet conformance and interoperability testing. The software is priced at $94,000.

It can test all the layers in an OSI seven-layer protocol stack. With the tool, users can create test scripts and all the functionalities needed by designers for developing an operations stack for a network element. Moreover, test scripts for OSI protocol stack layers 2, 3 and 4 help verify conformance to Bellcore`s GR-253-CORE Generic Requirements for Sonet Transport Systems (published in December 1994). They also cover the SDH international standards.

A key protocol supplied by Ocat is target address resolution protocol. It assists in making the translation from a numerical address to a named address. This critical process aids in the evolution to the common management information service element; Cmise is an application that sits on top of the seven-layer protocol stack. The Ocat software tests the protocols that allow the system to communicate among network elements, regardless of what application the user decides to implement.

Claims Leopold, "A future version of this software will have the ability to test the actual application layer and, therefore, have the ability to test Cmise objects. This capability would allow the identification of the final element of true interoperability--to be able to look at a set of objects and make sure they are implemented correctly."

According to Leopold, the Bellcore software was targeted at exhibiting Sonet interoperability via an implementation of a seven-layer OSI stack carrying Cmise. Another key Bellcore objective was to demonstrate that it could work with equipment suppliers and support the lightwave industry in getting seven-layer implementations into deployed networks. q

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