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What is (Voice over LTE/VoLTE):
Voice over long-term evolution (Voice over LTE/VoLTE) is a technology specification that defines the standards and procedures for delivering voice communication and data over 4G LTE networks. It is one method for creating, provisioning and managing high-speed voice, video and messaging services on a 4G wireless network for mobile and portable devices.
VoLTE primarily works on IP-based networks and only supports packet switching. The data received from a circuit-switched cellular network such as the Global System for Mobile Communications (GSM) or a Code Division Multiple Access (CDMA) network will be converted into network packets before being broadcast. VoLTE uses IP multimedia subsystem (IMS) based networks to offer these services. It will not work on networks that are not compatible with or that have not integrated IMS within their core architecture. The services that can be provisioned using VoLTE include video calling, voice calling, and multimedia streaming and sharing services.
Standardization for VoLTE services:
The GSMA VoLTE initiative has defined a minimum mandatory set of functions/features specified in 3GPP that an LTE device and the network are required to implement to guarantee an interoperable IMS based telephony/SMS service over an LTE/EPC radio access network. The document describing this minimum mandatory set, or profile, is called the “IMS profile for voice and SMS” and published as GSMA PRD IR.92.
IR.92 specifies the User-to-Network interface for VoLTE including:
- MMTel telephony and supplementary services
- IMS control and media handling
- EPC IP flow and bearer management
- LTE radio capabilities to be used
VoLTE basics
The different subsystems used in the solution are LTE RAN, EPC, IMS and UDM.
- LTE RAN
Handles the air interface towards the UE and involves functions such as Robust Header Compression (RoHC) and Discontinuous Reception (DRX).
- EPC
Handles the IP transport and control including; Policy control, Bearer management for QoS and P-CSCF discovery
- IMS
Handles service control and media; such as authentication, codec and jitter buffers handling, as well as supplementary service execution and provisioning.
- UDM
Handles subscriber for all the processes related with the Privacy, Authentication, Authorization and Mobility management of end users in mobile and converge Operators networks.
- CS core
CS core is needed for cases where user is outside LTE coverage
VoLTE provides all the necessary mechanisms for conversational voice service over packet data network, including; QoS, authentication, bearer management, policy control, supplementary services, regulatory services
End to End Call flow:
