The Design And Implementation Of IMS Access Gateway

With the continuous development of IMS technology, there is a major change in digital telephone system. Integration of different networks and different types of services become a trend in the development of digital telephone system. Traditional access gateway can not meet the needs of video, conferencing, group and other new multimedia services. And it can not support customized business. But, IMS is a unified platform for video, conferencing, group and other multimedia services, so IMS access gateway not only can meet the need of user, but also enriches the supported types of value-added products. It is in line with the new trend of network development.This paper combines with the project of digital telephone switching system. It is secondary development based on the Asterisk. We studied its network structure and the way that SIP gateway supported the dynamic SBC discovery mechanism and cooperation with the CM-IMS network to complete a call service. We analysed the supplementary service of the platform of CM-IMS and TDM PBX and designed the system structure of the IMS access gateway. We designed a way of generating routing list which is based on the prefix right and designed three relay selection strategies, including priority, rotary, rates. And we achieved a proxy registration, IMS access, intelligent routing and other media server functionalities and added the function of number conversion which is used to modify the caller and called number and achieved hot standby, firewalls and database modules.Finally, we set up a test environment and test the function of the system according to "China Mobile SIP Gateway Test Specification". The experiment proves that the design of the IMS Access Gateway can access to the IMS networks and support intelligent route selection, number conversion and standby switching functions and can remain stable performance in the case of high concurrency. It adds the support for IMS, video, conferencing and other multimedia services. It enriches the value-added products. It is in line with the development trend of the network and can meet the needs of users in terms of performance and user experience.