Next Generation Networks (NGNs), based on the Internet Protocol (IP), implement several services such as IP-based telephony and are beginning to replace the classic telephony systems. Due to the development and implementation of new powerful services these systems are becoming increasingly complex. Implementing these new services (typically software-based network elements) is often accompanied by unexpected and erratic behaviours which can manifest as interoperability problems. The reason for this caused by insufficient testing at the developing companies. The testing of such products is by nature a costly and time-consuming exercise and therefore cut down to what is considered the maximum acceptable level. Ensuring the interoperability between network elements is a known challenge. However, there exists no concept of which testing methods should be utilised to achieve an acceptable level of quality. The objective of this thesis was to improve the interoperability between network elements in NGNs by creating a testing scheme comprising of three diverse testing methods: conformance testing, interoperability testing and posthoc analysis. In the first project a novel conformance testing methodology for developing sets of conformance test cases for service specifications in NGNs was proposed. This methodology significantly improves the chance of interoperability and provides a considerable enhancement to the currently used interoperability tests. It was evaluated by successfully applying it to the Presence Service. The second report proposed a post-hoc methodology which enables the identification of the ultimate causes for interoperability problems in a NGN in daily operation. The new methods were implemented in the tool IMPACT (IP-Based Multi Protocol Posthoc Analyzer and Conformance Tester), which stores all exchanged messages between network elements in a database. Using SQL queries, the causes for errors can be found efficiently. Overall the presented testing scheme improves significantly the chance that network elements interoperate successfully by providing new methods. Beyond that, the quality of the software product is raised by mapping these methods to phases in a process model and providing well defined steps on which test method is the best suited at a certain stage.
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