Research And Implementation Of International Volte Roaming

VoLTE (Voice over LTE) is a technology for providing existing voice services on LTE based on IMS (IP Multimedia Subsystem) network. In VoLTE, IMS is responsible for control plane and LTE for user plane. LTE delivers all-IP communications with no dedicated voice infrastructure, e.g. circuit switch MSC/VLR. With the rapid development of the world economy, the rollout of international VoLTE roaming service will not only meet the user needs, but also strengthen the market competitiveness of operators themselves. Thus international VoLTE roaming becomes a very important topic in the development and deployment of LTE.In this paper, the international VoLTE roaming is studied, an open source project called OpenIMSCore is researched, and an international VoLTE roaming prototype system is implemented based on this project. Firstly, all relevant background knowledge is given, including related protocol specifications on IMS/VoLTE roaming and the technologies used in voice roaming. There exists one big problem that earlier VoLTE roaming architecture cannot use the voice call charging model of circuit-switched voice roaming architecture which has been used for a very long time. In order to address this problem and optimize the path of meida,3GPP and GSMA specify two logical functions from the perspective of control plane and user plane, refered as Loopback and OMR (optimal media routing). Secondlly, the open source project, OpenIMSCore, is studied, and international VoLTE roaming system is implemented based on this project. The main work include:1) since media anchor function was not included in OpenIMSCore, this function is implemented using JainSIP and efflux open-source framework to simulate the real architecture of the existing IMS system;2) the Loopback function is implemented by modifying the configuration files of P/I/S-CSCF and the source code processing SIP message;3) the OMR function is implemented by modifying SDP manipulation procedure in media anchor function. At last, six cases are tested to verify the functionalities of the two logical functions. Test results show that the Loopback function and OMR function in VoLTE roaming system is correct. And finally one international VoLTE roaming system is implemented.