us- tomer management, service management and resource management that partly E. Luoma et al. correspond to the TMN layers. The customer relationship management processes are responsible for having knowledge of customers' needs and the acquisition, enhancement and retention of a relationship with a customer. The service manage- ment processes are responsible for knowledge support in the areas of communica- tion, media and information services and the management and operations of these services for customers. The resource management processes are responsible for maintaining knowledge of resources (application, computing and network infrastructure), as well as for managing all the resources to support services for customers. The Telecom Application Map (TAM) defines the properties of OSS/BSS by combining specifications in the eTOM and SID frameworks into functioning applications. TAM is a framework for both those who sell and buy telecom software. TAM is in line with the vertical and horizontal grouping of the eTOM framework and basically it perpetrates the view that there might be at least one application for every single vertical process. 3 OSS/BSS Market 3.1 Market Segments In order to examine the vertical software market, an interpretation of the market in the form of segmentation is needed. Several market research companies (e.g., Dittberner, Lightreading, OSS Observer) have followed the evolution of the tele- com software market and classified firms operating in the industry into various market segments. The segmentation of the OSS/BSS markets followed in this book is based (1) on the definitions provided by these three market research companies, (2) on the Telecom Applications map, as well as (3) on the defined properties of the OSS/BSS software. Here, the OSS/BSS market has been divided into 13 segments, which have been positioned on top of the above-mentioned vertical processes and horizontal layers. Figure 1 presents this mapping of the OSS market segmentation on top of the operations process categories of