The modern OSS test

In the race to provide high-speed data services to residential and business customers, carriers not only have to provide new high-bandwidth service, they must provide it without replacing the existing outside plant.

Enter digital subscriber line technology. The ideal DSL solution does not replace major parts of the existing plant but augments them with DSL capabilities by integrating new hardware and software modules or systems as necessary. This approach allows the service provider to continue to benefit from existing investments while adding new technology where required.

But DSL service deployment and maintenance responsibilities present a brand new set of challenges to the service provider. To deploy DSL services successfully, the service provider must be ready to implement new business models and processes, provide training for operations and field personnel, and cope with new installation and support challenges.

DSL technology works well under ideal conditions. But existing OSP conditions are less than perfect. To provide optimum DSL performance, impairments and obstacles must be identified and eliminated, or in some cases, significantly reduced. In addition, equipment failures, improper equipment configurations and data network problems all affect DSL service.

Because DSL is optimized for data communications, customers want high-quality service and expect the service provider to isolate and correct any faults quickly and accurately. Service providers find themselves pulled from four different directions: Customers expect their high-speed data services to be easily available, low-priced, highly reliable and have minimum downtime. Carriers have neither the time nor the money to build new network operations centers, yet cost and downtime restrictions rule out testing methods that involve many truck rolls. What's a service provider to do?

Use what you have The challenges of managing DSL service activation and ongoing maintenance functions can be alleviated through the use of a modern operations support system (OSS). The OSS lets the service provider manage network operations by combining interactive and flowthrough testing, performance monitoring and administrative functions under a common architecture.

Today's essential OSS functions include sophisticated graphical user interfaces, programming interfaces, testing engines, network element interfaces and administrative services (Figure 1). The system uses a distributed architecture based on client/server principles and object-oriented technology. Such a system enables carriers to easily and efficiently manage testing resources and databases, as well as support reusable testing scenarios and complex test routines. The OSS also lets service providers support user-defined test scenarios to perform tests as quickly and effortlessly as possible.

DSL service implementation and subsequent maintenance can be broadly categorized into three phases known as prequalification, installation and maintenance. In this order, the phases are correlated with service provider activities and procedures. Installation and maintenance testing are similar and essentially include the same functionality, but they are applied differently.

An example of a DSL prequalification, installation and maintenance testing solution is shown in Figure 2. This solution is centered around an OSS installed at a service provider's network operations center. The system includes remote access, testing, performance monitoring and other capabilities necessary to support DSL services.

The DSL software modules in the OSS must control the remote test equipment for physical analysis of the DSL circuit and logical analysis of the fast packet network, as well as the metallic test access unit (MTAU) equipment. The software modules also include interfaces to element management systems, various service provider databases and data network equipment such as asynchronous transfer mode switches. These interfaces ease configuration, performance and fault analysis at all points within the DSL circuit.

In many cases, the remote test equipment is already in place and requires only the addition of DSL-capable plug-in modules. But in some cases, test equipment has to be added, especially at remote locations that previously did not carry data traffic. Ideally, all test equipment, whether existing or added, will be able to test both DSL circuits and other types of data circuits.

The software modules in the OSS provide on-demand testing for interactive applications as well as automated testing for flowthrough applications. The OSS manages the interfaces with external equipment and systems, and it can perform a comprehensive suite of tests. The user interface provides an integrated view of the DSL service without requiring the tester to manually access multiple systems. The OSS also provides database storage, benchmarks circuit test results from prequalification and maintenance testing, and analyzes test results.

The number of DSL circuits will dictate that service providers treat their DSL offerings like other traditional services, requiring the testing solution to include streamlined clerk interface and dialog capabilities. These capabilities will allow first-tier maintenance personnel to provide DSL testing and support while enabling higher-level technicians to perform additional enhanced DSL testing and analysis. This flexibility allows service providers to share this common tool among various operations centers.

Loop prequalification When offering DSL services, service providers need a low-cost way to ensure that the loop can support the service. By conducting physical loop analysis and examining copper plant records for the capability to support DSL, prequalification tells service providers which pairs cannot support DSL.

Prequalification, the first step when deploying DSL services, lets service providers offer DSL services within a specific geographic area with a degree of certainty that the service can be delivered as advertised.

Prequalification is most cost-effective and practical if it is performed from centralized locations without the need to reconfigure existing services. To prequalify large numbers of copper pairs, the prequalification software module of an efficient DSL testing solution will provide automated bulk testing, including centralized single-ended measurements and loop analysis using the existing infrastructure for narrowband services.

However, in addition to supporting automated bulk prequalification testing, the OSS must also support on-demand or pass-through prequalification. On-demand prequalification lets a user quickly perform a test for a circuit that may not have been prequalified or reapply the test to confirm the state of a circuit. On-demand testing should be available to nontraditional testers through a streamlined clerk interface to avoid tying up more skilled troubleshooters.

The prequalification software module must support both immediate and scheduled tests on a single telephone number or a range of numbers. Range tests support parameters that allow finer control of the test. These parameters allow testing of a subset of the entire range of circuits based on input criteria, as well as repetitive testing of a range of circuits. Users must be able to specify test resource information for tests scheduled in parallel, and they must create execution log files.

The multitasking capabilities of a modern OSS will allow tests to be scheduled in parallel, with the number of simultaneous tests limited only by the physical test resources available. The list of scheduled jobs must be viewable at any time, and a tester needs the administrative ability to delete jobs as needed. Test results must be available on any circuit or range of circuits at any time for either scheduled or immediate tests; the status of a test in progress must be viewable as well.

In an incumbent local exchange carrier environment, loop access for prequalification testing can be gained via a number test trunk access from a POTS end-office switch as shown in Figure 2.

In a competitive LEC environment, loop access is provided by the CLEC-controlled MTAU equipment. In either case, the OSS controls the remote test unit and metallic test access equipment.

In addition to physical loop analysis, an interface to the facilities database provides identification of loops that are served by digital loop carrier systems and loops that could suffer from high-capacity digital service interference. The OSS combines this information with the physical loop test results and applies the service provider-defined acceptance templates to produce prequalification results for the specific DSL service.

Installation and maintenance The second and third testing phases, installation and maintenance, occur after a loop has been prequalified and the DSL service has been offered to the subscriber. Installation testing is in some respects an extension of prequalification but primarily aids in service activation and problem resolution. After the carrier turns up DSL service, it performs maintenance testing to resolve problems and ensure the continued integrity and performance of its service.

Installation and maintenance testing capabilities should include wideband physical loop analysis, logical analysis and interfaces to element management systems (EMSs), ATM systems and service provider databases. This comprehensive testing approach enables carriers to quickly identify DSL circuit problems as inside or outside plant facilities, or as equipment problems.

The OSS controlling the DSL installation and maintenance testing process must possess the necessary functionality to interface with multiple systems, control test functions, collect data and produce pertinent information. The system collects signal analysis and test results from the test equipment, as well as configuration, performance and fault data from the network elements. Additional analysis must be applied to this data to produce useful information. The system should provide suggestions as to the nature of a problem and steps necessary to further isolate or resolve the problem. The OSS must also support storage, benchmarking and comparison functions that are applied to this information.

The OSS must provide support for interactive and automated flowthrough testing applications. In the interactive scenario, graphical plotting and representations are presented to the user. In the automated flowthrough environment, the system interacts with other service provider systems to automatically perform test and analysis functions and post the results.

Figure 3 shows the key components of an installation and maintenance testing solution. Installation testing is applied after the subscriber line is wired through DSL access multiplexer (DSLAM) equipment in the central office or other location. With an interface to the service order system, the OSS can be triggered to perform installation testing automatically, based on specific service order criteria.

Installation tests definitively assure that the copper pair can support the DSL service. This step lets service providers verify the loop for DSL service and allows the installation process to proceed with less chance of a problem developing or the need for multiple dispatches.

Installation testing is extended to the service activation process. During this phase, wideband physical loop analysis should measure the performance of the loop, including upstream and downstream signal levels and power spectral density. It also should identify potential noise sources and faulty equipment. The signatures of the DSL transmission unit-central and DSL transmission unit-remote equipment, where defined, should be verified to ensure proper connectivity.

As part of the service turn-up, the installation phase of DSL deployment should include tests to confirm that the service is functioning properly. These tests should identify equipment failures (upstream and downstream), configuration errors and data network problems. The installation and maintenance software module should retrieve configuration information from the DSLAM EMS to determine if a specific circuit is configured and performing correctly. By interfacing with the service provider's DSL inventory database, the system can identify discrepancies between the database and the information from the DSLAM. Interfacing with the EMS will provide equipment and line information and in some cases, control of the built-in testing functions of the DSLAM and DSL modem. In addition to physical loop and related equipment problems, protocol problems may exist that prevent DSL service from working properly. The OSS should include a protocol testing module that uses the ATM switch and a remote protocol analyzer system to determine upstream data network problems. The OSS database interface software and the protocol testing module must determine if the DSL data stream's virtual channel is configured correctly and facilitates inquiries to the ATM switch for the status of the virtual channel. This ATM switch interface provides a quick indication of upstream ATM cell flow and virtual channel performance. The OSS should include a protocol analysis feature to enable the user to identify customer equipment-related protocol and configuration problems.

The final phase, maintenance testing, should follow the same principles as installation and service activation testing. The difference is that maintenance testing occurs after the service has been offered to the customer. As part of maintenance testing, the OSS should also include a DSL performance monitoring feature. Practically all DSLAM vendors collect performance information via either the EMS or the DSLAM itself.

Performance monitoring is essential to protecting the quality of network services. The performance monitoring system's actions can be automatically triggered in response to events, routinely executed on a scheduled basis, or initiated by operators on demand. If services start to degrade, technicians in the test center can proactively perform comprehensive logical and physical testing to isolate the problem.

Putting it all together As the rate of installation of DSL circuits continues to grow, carriers are faced with an ever-expanding drain on their already-scarce resources. A modern OSS achieves the necessary DSL service management goals. These operations include prequalification, installation and maintenance functions to facilitate smooth service activation and ongoing maintenance activities.

Today's OSS must be diverse, flexible and scalable, while supporting various interfaces to existing equipment, systems and databases. The system must include graphical user interfaces and functions that provide an end-to-end view of the DSL service for interactive testing, as well as support for automated flowthrough testing applications. After testing has been performed and data has been gathered, the OSS must provide information storage, retrieval, benchmarking and expert analysis.

Using a comprehensive DSL testing solution based on a modern OSS and test equipment is the ideal approach to come to grips with the DSL service management problem in an efficient, cost-effective manner.