Call Control in Voice over LTE systems

OData support
Dr. Varga Pál
Department of Telecommunications and Media Informatics

In August 2013 I took up dealing with the VoLTE technology: with the IMS (IP Multimedia Subsystem) tools, and the used SIP (Session Initiation Protocol) messages. During my research I have got to learn the existing VoLTE solutions and the links and protocols of IMS. Due to the increasing demand for high quality voice services for 4G mobile technologies, the VoLTE realization and the call control through SIP messages became the chosen theme of my thesis. I had the opportunity to get documents and actual monitored messages, since the Magyar Telekom Inc. deals with this topic and establishes calls in its lab.

Thanks to my earlier experiences of network monitoring, I thought that investigating how SIP calls work can help to make a proposal for the solution of SIP Call Data Records based on protocol monitoring. During my work – and with the great help of experts from AITIA International Inc. – I developed a well functioning algorithm as a solution to this problem. I checked many cases, so I got to know the structure of the dialogs, the parameters and the messages. I have developed a C++ software, that processes plenty of messages and collects the unusual cases. Tamas Tothfalusi, who works at Aitia International Inc., has helped me to improve my software.

At the end of the tests, I have created many statistics by the help of this software. These statistics can help developers who deal with this problem set, to have broader view. My main goal was to help the telecommunication developers with the tasks of VoLTE systems. During the semester I learned in detail how SIP works, and learned the architecture of LTE. I have gained broad experience in IMS architecture by the help of Magyar Telekom's networking experts (and their equipment) in centres of Kelenföld and Szava street.


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