Voice Services to LTE Users

Telecom Regulatory Authority of India (TRAI) has released a consultation paper (CP) on Voice Services to LTE users (including VoLTE and CS Fallback). Earlier, TRAI had notified the fifth amendment of The Standards of Quality of Service of Basic Telephone Service (Wireline) And Cellular Mobile Telephone Service Regulations, 2009 on August 18, 2017.

The fifth amendment of regulations redefined a new QoS framework for drop call rate (DCR) assessment and the DCR benchmark was fixed in technology agnostically.

Accordingly, from a DCR benchmark and measurement perspective, a network’s performance on all technologies (e.g., 2G, 3G, or 4G) deployed by the TSP in LSA and used for providing voice services is treated equally. After this amendment, the consolidated data of all the cells of the TSP is being used to be assessed as part of a single network, irrespective of the technology being used, that is whether cells belong to GSM, CDMA, WCDMA, or LTE.

To provide voice services via LTE, both VoLTE and CSFB techniques may face some quality of service issues due to different network scenarios. Such scenarios may result into a silence period or voice mute observed by the users. Extent to which this is experienced by the user during a call before dropping of a call may also be implementation specific.

This paper discusses the growth of LTE networks and various migration paths followed by different Indian TSPs for providing voice services via LTE. The paper highlights various options for providing voice services in LTE network like VoLTE, CSFB, single radio voice call continuity (SRVCC) etc. It discusses about the handover scenarios of calls in CSFB and the evolution of performance of CSFB in different 3GPP releases of LTE.

It also highlights parameters that are defined in ITU standard G.1028, 3GPP TS 36.331, and GSMA IR.42, which can measure various causes of degradation in quality of voice calls in the LTE network which can lead to poor customer experience.