Design Of Call Server Of SoftSwitch And Realization Of Its High Availability

The SoftSwitch which is on the controlling layer of the NGN(next-generation networks), is of the most important of the process from the traditional circuit-switch based networks to the packet-switch based networks. It is independent of the lower transmitting protocols and is mainly responsible for functions such as call controlling, media gateway access controlling, resource distribution, protocols processing, routing, authentication, charging and so on, and it can supply all of the services and multiple third-party services for subscribers of the circuit-switch based networks. As the core controlling equipment of the SoftSwitch networks, the call server is responsible for functions such as call processing, protocols access adapter, service interfaces, connection, application supporting and so on. The big capability and centrality of call server make it as one of the key part of SoftSwitch.This paper gives a general software architecture of call server first, on the lowest layer of which is the signal protocols accessing module, on the middle layer of which is the call controlling layer, which is made up of the call processing module, the media gateway controlling module and the route and resource management module, and on the highest layer of which is the service switch module. On the condition of this general software architecture, the paper gives a expatiation of the basic model of the call processing module, which is suggested as the basic call state model on the Q.1214 of ITU-T. In practice, there are many design thoughts of the basic call processing module. This paper gives two designs about the basic call processing module, one of which is the message-based-distributed fsm(finite state machine) and the other is the event-based-distributed fsm, which gives more assurance of the high availability comparatively.After the discussion of the realization of the call server, this paper describes the architecture of the high availability and its constituted module. On the basis, the paper describes the realization of the finite state machine, the process of data synchronization and the memory unit allocation arithmetic and its unit test method. In the end, this paper describes the system test method of the high availability of call server and its performance.