The Telecom Regulatory Authority of India (Trai) today released a consultation paper on ‘Voice Services to LTE users (including VoLTE and CS Fallback).’ In the paper, Trai discussed the growth of LTE networks and various migration paths followed by different Indian telecom service providers for providing voice services via LTE. The paper also highlights various options for providing voice services on an LTE network like VoLTE, Circuit Switch Fall Back (CSFB), Single Radio Voice Call Continuity (SRVCC) etc. It discusses about the hand over scenarios of calls in CSFB and the evolution of performance of CSFB in different 3GPP releases of LTE. It also highlights parameters which are defined in ITU standard G.1028, 3GPP TS 36.331 and GSMA IR.42, which can measure various causes of degradation in the quality of Voice calls in LTE network which can lead to the poor customer experience.
Trai is seeking comments on the issues raised in the consultation paper from stakeholders by March 16, 2018, and counter comments by March 23, 2018.
Earlier, the 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 new QoS (Quality of Service) framework for Drop Call Rate (DCR) assessment, and DCR benchmark was fixed in technology agnostically.
Accordingly, from a DCR benchmark and measurement perspective, a network’s performance on all technologies, for example, 2G, 3G or 4G deployed by the TSP in an LSA and used for providing voice services are treated equally. After this amendment, the consolidated data of all the cells of the TSP is being used to assess as part of a single network, irrespective of the technology being used, i.e. whether cells belongs to GSM, CDMA, WCDMA or LTE.
As you all might be aware of, LTE is an all-lP, data-only transport technology based on packet switching. Voices services in LTE network is mainly carried by two technologies viz. Voice over LTE (VoLTE) and Circuit Switch Fall Back (CSFB). VoLTE allows carriers to transmit voice calls over LTE network and controlled through their IP Multimedia Subsystem (IMS). This means that voice calls and data sessions travel side-by-side over LTE. Whereas in CSFB, LTE network is used only for data traffic and voice services are provided on traditional circuit-switched technologies of 2G and 3G. CSFB redirects a device registered on the LTE network to the 2G/3G network (i.e. fallback) prior to originating or receiving a voice call.
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 in silence period or voice mute observed by the users. The extent to which this is experienced by the user during a call before dropping of the call may also be implementation specific said Trai in the paper.