VOLTE deployment scenarios: Perspectives and performance assessments

The LTE “Long Term Evolution” technology was introduced to reduces the DATA network latency, in addition to provide higher data throughput. But the nature of LTE prohibits the transmission of voice related services. VoLTE “Voice over LTE” is a solution to transfer voice packets with special treatment over the LTE network, and get benefits from its low latency and quality of services capabilities to have voice services jointly provided by the EPC “Evolved LTE packet core” and the IMS “IP Multimedia Subsystem”. As VoLTE is a new technology for both network and devices providers, it has some limitations in providing all voice related services over LTE. Network initiated and user initiated USSD “Unstructured Supplementary Service Data” are not supported directly over VoLTE. CSFB “Circuit Switched Fall Back” is a temporary solution used to instruct the VoLTE device to fall back to CS “Circuit Switching” network to receive such USSD, then returning back again to VoLTE after completing the reception of the USSD. If the VoLTE network tried to push a USSD notification to a VoLTE subscriber who is engaged in one or more voice calls “conference call”, the commercial network settings will make that subscriber to release all the LTE bearers to fall back to the CS network which causes the drop of all active calls owned by that VoLTE user, which affects negatively on one of the most important VoLTE QoS “Quality of service” parameters which is service availability. A novel solution will be introduced to overcome such limitations and prevents any active voice call from being dropped when receiving a USSD from the VoLTE network. This will be achieved by using SRVCC “Single Radio Voice Call Continuity” instead of CSFB when receiving USSD while being engaged in a voice call. To verify such novel method, a real pilot VoLTE network is used to get practical traces and measurements to validate that novel solution to achieve such important QoS parameter. The performance of that solution is evaluated by measuring the call drop rate improvements achieved by that novel technique.