| In various services that NGN provides, Centrex service based on SoftSwitch is an enterprise service that many carriers and subscribers attend. Not only it can ensure the primary income for the carriers, but also it can provide economical and convenient communication solution for the subscribers. This paper starts with the background and development of NGN, and then introduces system architecture of SoftSwitch, which is the key technology of NGN. After that, it analyzes the Basic Call State Model, and enlarges upon Half-Call model and Call Party Handling capabilities in Intelligent Network. Half-Call model is the basic to realize various intelligent services, and CPH ensures that we can control and manage every subscriber's connection in any call processing state. For the design and realization of common intelligent service, we mainly consider how to realize CPH capabilities. CVS adopts object-oriented methods, and describes connection states in current call processing by defining logic objects (such as CS, Leg) and relationships between these objects. CVS provides a simple and intuitive way for complicated multi-party call processing. While designing Centrex service based on SoftSwitch, we define specific Centrex application server. For dealing with call pickup service, we bring forward a new CVS model. Since the two parties after call pickup are both callers, surrogating function is needed in callee side. Call transfer service has a reference to transfer CVS of IN CS-2. For statistics and Call Detail Record of call transfer service, the paper brings forward a call-divided model that is convenient to maintain and manage. When subscribers transfer the call several times, processing is similar with transferring once. Finally, we create system integrated test platform, configure related NMS data and write test cases. The test result shows that SoftSwitch system designed in the paper can execute required Centrex service accurately, and reaches the expectant design requirements. |
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