al when compared to other markets due to the eTOM business process standardization effort driven by TM Forum. Standardizing the OSS/BSS processes, data model and a common set of interfaces for applications have been well appreciated (although not yet fully adopted) by telecom operators and especially by IT integrators. Software related to network equipment has traditionally been vendor-specific. Later, network technology standardization has been very active and new standards have been created at a fast pace. Each new network technology with different performance characteristics required new software. Thus the number of network interfaces to be integrated to OSS/BSS software has been overwhelming prohibit- ing OSS/BSS software from reaching a steady market with a single dominating design. Telecom operators, having invested heavily into previous generations of net- work infrastructure, are forced to maintain the legacy systems till the end of their investment demortalization period. Simultaneously they are forced to provide new services enabled by new technology both to new customers and to the existing customer base connected with old network technology. When the software product vendors have not been able to support a full set of legacy technologies, the large Preface established operators have been forced to use IT integration services and in-house development much more than small communications service providers (CSPs), which have preferred the use of products from smaller vendors. There have been various attempts to evolve the vertically integrated, technolo- gy-specific OSS/BSS software architecture to a vertically disintegrated, layered, network technology independent architecture. This has succeeded best at the customer interface layer with the aid of generic software vendors adapting their horizontal software for the requirements of CSPs'. At the service layer the attempts known as IMS, service delivery platform or framework have remained merely as approaches enforcing an engineering discipline while reduc