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| Voice over LTE | |
|---|---|
| Name | Voice over LTE |
| Acronym | VoLTE |
| Introduced | 2012 |
| Developer | 3GPP |
| Type | Voice over IP |
| Standard | Long-Term Evolution |
| Related | IP Multimedia Subsystem, Rich Communication Services |
Voice over LTE is an IP-based telephony service that delivers voice calls over Long-Term Evolution data networks using the IP Multimedia Subsystem and Session Initiation Protocol signaling. Developed within the 3GPP standards process and deployed by operators such as Deutsche Telekom, AT&T, and NTT Docomo, it replaced circuit-switched voice on many modern mobile networks while enabling services tied to Rich Communication Services, Voice over Wi‑Fi, and multimedia communications. VoLTE intersects with technologies and institutions including IMS Core, Evolved Packet Core, 3GPP Release 8, and industry testing by organizations like GSMA.
VoLTE provides native packet-switched voice on Long-Term Evolution networks by using the IP Multimedia Subsystem framework and codec negotiation such as Adaptive Multi-Rate Wideband (AMR‑WB). Major vendors including Ericsson, Nokia, Huawei, and Samsung Electronics implemented VoLTE in commercial networks run by operators including Verizon Wireless, Vodafone Group, Orange S.A., and Telefonica. Standardization occurred across 3GPP Releases and coordination with bodies like ETSI and the ITU. Market adoption has been driven by handset support from manufacturers such as Apple Inc. and Google LLC and by ecosystem work from platform vendors including Qualcomm and MediaTek.
The architecture uses the Evolved Packet Core and IP Multimedia Subsystem to route media and control functions; key network elements include the Mobility Management Entity, Serving Gateway, and PDN Gateway. The IMS control plane contains the Call Session Control Function and Proxy-CSCF, Interrogating-CSCF, and Serving-CSCF components. Media flows typically use RTP with Secure Real-time Transport Protocol for encryption and negotiate codecs such as AMR-NB, AMR-WB, and sometimes Opus in advanced deployments. Radio-layer integration leverages Evolved UMTS Terrestrial Radio Access Network and signaling over the LTE radio link using Radio Resource Control procedures. Roaming and packet routing often reference protocols and specifications defined by 3GPP SA3 and interconnect arrangements among operators like T-Mobile US and international carriers.
Call setup and teardown rely on Session Initiation Protocol messages handled by IMS entities; features such as call forwarding, call waiting, and supplementary services map to IMS and legacy IN services. Interworking with legacy Public Switched Telephone Network signaling uses gateways implementing Media Gateway Control Protocol or interconnects via IP Multimedia Subsystem breakout functions. Operators implement charging and policy control through Policy and Charging Rules Function and Online Charging System integrations. Standards work in 3GPP SA1 and 3GPP SA2 define state machines and procedures used by vendors like Cisco Systems and Alcatel-Lucent for call control implementations.
Quality assurances use LTE Quality of Service Class Identifiers (QCIs) and policy controls from Policy and Charging Rules Function to prioritize conversational voice traffic; real-time media is often marked for low-latency treatment. Emergency calling integrates IMS emergency procedures and location technologies including Enhanced-911 services in the United States and equivalents in regions regulated by entities such as the European Commission and national regulators like Ofcom. Implementation of emergency services requires coordination with emergency services infrastructure, often involving standards from 3GPP and work by organizations like IETF and GSMA on location and routing requirements.
Commercial launches began in the early 2010s, with leading deployments by SK Telecom, Sprint Corporation, and Telstra. Operators phased out circuit-switched fallback as IMS maturity increased, with handset vendors enabling native support in operating systems from Apple Inc. (iOS) and Google LLC (Android). Network rollout strategies varied: some operators used VoLTE-only architectures, others maintained CSFB fallback for interoperability. Key vendor ecosystems include Huawei Technologies, ZTE Corporation, Cisco Systems, Nokia Networks, and testing by industry bodies such as PTCRB and GCF.
Interoperability requires IMS roaming agreements, codec negotiation, and interconnect arrangements among operators and international carriers such as British Telecommunications and China Mobile. Roaming complexities include handling of emergency calls, voice continuity between LTE and legacy networks, and supplementary services; solutions involve SIP-I/SIP-T interworking and media gateways. Global roaming profiles and operator alliances facilitated by GSMA define mandatory features and testing regimes to ensure handsets from manufacturers like LG Electronics and Sony Corporation behave consistently across networks.
Security mechanisms include mutual authentication via Evolved Packet System Authentication and Key Agreement, integrity protection and confidentiality for signaling, and use of IPsec or TLS between IMS elements; media is commonly protected with SRTP. Privacy and lawful intercept obligations engage national authorities such as Federal Communications Commission and legal frameworks including statutes in the United Kingdom and the United States. Security research from academic institutions and vendors including MIT, Stanford University, and Carnegie Mellon University has highlighted threats such as IMS signaling vulnerabilities and session hijacking, prompting vendor patches and operator mitigations.
Category:Telecommunications Category:Mobile telephony