scope:

This Recommendation works on the assumption that Voice over LTE (VoLTE) is a so-called ''managed'' voice service, in opposition to over the top (OTT) applications without use of session initiation protocol/IP multimedia subsystem (SIP/IMS) signalling and with no prioritized traffic. Video-telephony over LTE (ViLTE) is another service which is addressed in the specific Recommendation [ITU-T G.1028.2].

This Recommendation describes the key aspects impacting end-to-end performance of managed voice applications over LTE networks, for the most common call cases including circuit switched fall back (IMS tromboning is not considered, nor single radio voice call continuity (SRVCC), nor mobility under wireless local access network), and how they can be properly assessed using current elements of knowledge.

Relevant quality of service (QoS) mechanisms used to manage the voice service, such as robust header compression (RoHC), transmission time interval (TTI) bundling, semi-persistent scheduling (SPS), discontinuous transmission (DTX) and reception (DRX), service domain selection (SDS) or SIP preconditions, are not considered in this Recommendation as a mandatory part of a VoLTE service, but their impact on end-to-end perceived quality will be taken into account.

Analysis of the impact of VoLTE on quality of supplementary services (such as data streaming) or on device features (battery life) is outside the scope of this Recommendation.