This book describes how the mobile network is managed using OSS (Operational Support Systems). Mobile service providers follow the DBOM (Design, Build, Operate, and Maintain) process to run the business using OSS products (assurance, fulfillment, billing). Mobile services are managed using the core functions of network management which are referred to as FCAPS (Fault Management, Configuration Management, Account Management, Performance Management, and Security Management). These Management functions in each layer of TMN (Telecommunication Management Network) are explained in detail to understand the principles, data flow, and use cases. While the first two phases of the DBOM process are the core business for the operator to leverage the business goal. Operating and maintaining the network becomes the option for outsourcing as 'The Managed Services.' Quality Assurance (QA) function is to validate the DBOM process. This book explains the end-to-end mobile service operations in the capacity of data flow (FCAPS) and operational workflow management. A mobile network is a heterogeneous network that includes a multi-technology-radio access network, circuit-switched core, packet-switched core, transport network, multimedia systems, IP network, and service platforms. A separate management system manages each technology. The services from these networks deliver the user services such as voice, data, messaging, roaming, and other value-added services.