uld be followed by the service developer to ensure interoperability and ease of integration. The issues that originate in a multisupplier/partner environment with acquisitions/mergers can only be addressed using standardization. Transformation of legacy application is also a strategy followed by many ser- vice developers. Since legacy solutions are functionality rich, many service developers don't opt for new SOA-based solutions, rather they transform their legacy solution in stages to an SOA-based framework. COTS software and hardware developed with holistic telecom vision should be used by service developers in the solutions they offer to service provider. Off the shelf implementations will reduce cost and integration time. The challenge is to ensure that a COTS product will interoperate as expected with an exist- ing product. NGOSS based applications should allow solutions to be rapidly implemented through integration of off-the-shelf software components. ATCA (Advanced Telecommunications Computing Architecture) is a modular com- puting architecture from PICMG for COTS telecom hardware development. Let us conclude the discussion by mentioning some of the key players that offer assurance solutions. After acquiring Tivoli Systems Inc. and Micromuse, IBM has emerged as the market leader in offering a variety of assurance solutions. HP Openview products of Hewlett-Packard (HP) can manage and monitor a wide vari- ety of network elements used in data, access, and transport network. Computer Associates have a suite of solutions for management of application servers. TTI Telecom offers OSS service assurance solutions suited for fixed, mobile, and cable networks. Telcordia is another OSS solutions provider worth mentioning in the market leaders for assurance solutions. 20.4 Billing Process Billing corresponds to the processes in service provider space for getting revenue from the customer for the services consumed. The service used by the customer is metered for generating the bill. There is a rate associated with the 