Assembling SIP-based VoLTE Call Data Records based on network monitoring

Abstract

The Voice over LTE (VoLTE) service is under deployment at many operators. Although it has great promises--from high service flexibility to previously unseen QoS measures--so far it poses more challenges than expected. The serving architecture is diverse, and the flexible services mean variable use-cases with complex message sequence charts. In order to be able to control the procedures--during deployment as well as during the operation--we need to have proper network and service management in place. Such a management framework includes network and service monitoring tools that help to provide better visibility of the various procedures. For the VoLTE service, both the LTE Evolved Packet Core (EPC) and the IP Multimedia Subsystem (IMS) need to be monitored. Network-wide data capture and analysis for the EPC and the IMS require new processing methods. These would allow operators to correlate control and user plane information of various interfaces and protocols. There are many obstacles to overcome here, including ciphered control messages and global identifiers hidden by temporary ones. This paper presents a system for SIP Call Data Record assembling, shows what kind of key parameters have to be extracted in order to enable expert analysis. After going into the details of messages, transactions, and dialogues, we present Call Data Record assembling methods for various scenarios. Furthermore, we present methods on how to gather cross-correlated data on specific fault management use-cases, particularly for unsuccessful voice calls.