Voice over LTE, or VoLTE is a GSMA profile of the standards definition for the delivery of
Packet Switched only network of LTE, leveraging the core network IP Multimedia SubSystem (IMS). When mobile networks deploy LTE radio access technology, conformity to
the VoLTE profile provides operators with assurance of interworking between their LTE
network and the devices that connect to it, as well as providing for the expected user
experience of voice Multi-Media Telephony service and SMS. In combination with Policy
Control, IMS provides for the required QoS appropriate for voice service using LTE radio
access technology, thereby providing the user experience of voice calls that subscribers
expect. Moreover, VoLTE is designed to fully integrate with the existing user experience that
is currently implemented with circuit switched voice devices, and therefore whether the call
is a circuit switched call or a VoLTE call is transparent to the end user (including when
moving in and out of LTE coverage) and is dependent only on which radio access
technology to which the user is attached. At the same time, using new, wideband codecs
can provide higher voice quality and enhance the user experience.
VoLTE is in accordance with 3GPP specifications and additional profiling is defined within
GSMA Permanent Reference Documents.
GSMA PRD IR.92 [54] defines the UNI for IMS voice and SMS. It defines a profile that
identifies a minimum mandatory set of features which are defined in 3GPP specifications
that a wireless device (UE) and network are required to implement in order to guarantee an
interoperable, high quality IMS-based telephony service over LTE.
The NNI for VoLTE is defined in the IMS Roaming & Interworking Guidelines GSMA PRD
IR.65 [51].
VoLTE Roaming is defined in the LTE Roaming Guidelines GSMA PRD IR.88 [53].
This document defines the VoLTE service description and implementation guidelines in
order to provide an end-to-end VoLTE deployment.
Note that in this version of the document, CSFB and SRVCC are not in scope.
- Relationship to Standards
VoLTE is based on publically available and published 3GPP specifications as listed in
Section 1.5. 3GPP Release 8, the first release supporting LTE, is taken as a basis for the
VoLTE profile. It should be noted, however that not all the features mandatory in 3GPP
Release 8 are required for compliance with VoLTE.
Conversely, some features required for compliance with VoLTE are based on functionality
defined in 3GPP Release 9 or higher releases.
Unless otherwise stated, the latest version of the referenced specifications for the relevant
3GPP release applies.
Detailed information related to the support of specific 3GPP functionality per release is
defined
- Scope
This document is separated into 5 main sections.
Section 2 VoLTE Architecture:- defines the logical architecture, functional node
description, and interfaces required for VoLTE deployment.
Section 3 VoLTE Implementation – Single PMN:- defines what is required to deploy
VoLTE within a single MNO's domain; detailing call flows, supplementary services
required, Diameter configuration aspects, traffic management and QoS aspects,
security, etc.
Section 4 VoLTE Implementation – Interconnect:- defines what is required in
addition to an Intra-PMN deployment, for interconnecting two MNO's VoLTE
deployments; detailing call flows, bi-lateral interconnect, IPX interconnect,
ENUM/DNS, usage of Session Border Controllers, etc.
Section 5 VoLTE Implementation – Roaming:- defines what is required in addition to
an Intra-PMN deployment, for allowing subscribers to roam between two MNO's
VoLTE deployments; detailing call flows, Local-BreakOut (LBO), Impacts to
Diameter routing, policy and QoS aspects, etc.
Section 6 Implementation Guidelines:- highlights the issues discovered during
VoLTE Interoperability testing (IOT) and in commercial operator deployments.
- Definition of Terms
3GPP= 3rd Generation Partnership Project
A-SBC= Access Session Border Controller
ACR= Anonymous Call Rejection
AMBR Aggregate Maximum Bit Rate
AMR=Adaptive Multi-Rate
AMR-WB= Adaptive Multi-Rate Wideband
API= Application Programming Interface
APN= Access Point Name
ARP= Allocation and Retention Priority
AS= Application Server
AUTN= Authentication Token
AVP= Attribute Value Pair
BGCF= Border Gateway Control Function
BICC= Bearer Independent Call Control
CAMEL= Customised Application for Mobile network Enhanced Logic
CDIV= Communication Diversion
CDR= Charging Data Record
CN= Core Network
CONF= Conferencing