VoLTE is built on a stack of 3GPP (3rd Generation Partnership Project) specifications. The key documents are:
| Specification | Title | VoLTE relevance |
|---|---|---|
| TS 22.173 | IMS Multimedia Telephony service and supplementary services | Service requirements for IMS voice |
| TS 23.228 | IP Multimedia Subsystem (IMS) stage 2 | IMS architecture – the foundation document |
| TS 24.229 | IP multimedia call control protocol based on SIP and SDP | SIP/SDP procedures for VoLTE call setup |
| TS 24.301 | Non-Access-Stratum (NAS) protocol for Evolved Packet System | EPS bearer management including QCI 1 bearer setup |
| TS 26.114 | IMS conversational video and voice; media handling and interaction | AMR-WB codec use in VoLTE, jitter buffer requirements |
| TS 26.441 | Codec for Enhanced Voice Services (EVS) | EVS codec used in VoNR and some VoLTE implementations |
| TS 36.331 | E-UTRA Radio Resource Control | LTE RRC procedures including dedicated bearer setup for VoLTE |
The GSMA (GSM Association) produces implementation profiles that ensure interoperability between operators. For VoLTE, the key document is:
| Specification | Title | Purpose |
|---|---|---|
| IR.92 | IMS Profile for Voice and SMS | The mandatory VoLTE interoperability profile. Defines exactly which 3GPP features operators must implement for handsets and networks to interwork. The most important VoLTE standard after 3GPP TS 23.228. |
| IR.94 | IMS Profile for Conversational Video Service | VT (video telephony) interoperability profile for VoLTE video calls |
| IR.51 | IMS Profile for Wi-Fi Calling | VoWiFi interoperability, same IMS as VoLTE |
| IR.92 Annex B | Device requirements | Specific requirements for handsets claiming VoLTE compliance |
Ofcom regulates UK telecommunications. Its Communications Market Report tracks VoLTE adoption, call quality metrics, and network performance. Ofcom has monitored the impact of the 3G switch-off on consumers and business users and has published guidance on the PSTN migration.
Openreach’s Digital Voice programme is the industry-wide programme to migrate the UK’s telephone infrastructure from the PSTN to IP-based delivery. The January 2027 closure date affects all analogue lines. Openreach has published guidance for housing associations, businesses, and equipment manufacturers on the migration path.
Safety rules for the construction and installation of lifts – Rescue of persons in stalled lifts. Requires a two-way communication system in every lift car capable of contacting a rescue service. This standard is the primary driver for VoLTE adoption in lift installations replacing PSTN emergency phones.
Fire safety requirements relevant to alarm communicators. Grade D fire systems may use voice communicators; these must be reviewed against the PSTN closure timeline.
UK standards for intruder alarm systems design. Systems using PSTN-connected diallers for ARC signalling must be reviewed against the 2027 deadline. BS 8243:2021 covers the use of cellular transmission paths for alarm signalling.