payable. Telecom bills are mostly complex and error prone. This leads to high invoice process- ing costs. Use of an invoice management solution reduces cost per invoicing. Other advantages include a faster invoice approval and collection process. This leads to an increase in efficiency caused by improved financial reporting. Fundamentals of EMS, NMS and OSS/BSS Some of the key features of an invoice management solution are invoice consolidation, invoice auditing, invoice content validation, tracking of invoice, getting approvals, generating intuitive reports, and smooth integra- tion with accounting system. 12. Billing mediation: A billing mediation application collects billing data from multiple sources, filters them, and does formatting and normalization before sending it as a single feed to the billing system. Converged billing mediation solution can collect billing data from IP, fixed, and mobile networks. The activities performed by billing mediation application can be summarized as gather, process, and distribute of usage data. The tasks start with collection and validation of usage records. This is followed by filtering out irrelevant records that are not relevant for billing. Records are then aggregated and correlated to obtain useful information. Finally the usage data is formatted and normalized. Then it is distributed to northbound OSS applications. It should be noted that all data mediated by the billing mediation system is not used by the billing system. For example, some traffic information can also be obtained from the records that could be used in capacity planning rather than billing. Also mediation systems can be used to execute commands like provisioning tasks. 13. Network optimization: The main aim of network optimization solution is to improve the network performance and ensure effective utilization of resources. Optimization would involve changes in operations modeling. This is done to ensure that the service and network performance achieves the ser- vice level parameters shared with the cus