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Standards

Public Warning Systems

Public warning over 5G Broadcast carries emergency alerts as CMAS messages in SIB12 (ETSI TS 103 720 V1.2.1 clause 5.15.3.3) to any receiver in coverage, using the same free-to-air LTE-based broadcast carrier as linear TV and radio. Because it needs no SIM, no subscription and no return channel, it keeps working when the cellular network is congested or unavailable, which is exactly when warnings matter most. The earthquake and tsunami warning system (ETWS) is named in ETSI TS 103 720 only as a regional adaptation of PWS (clause 4.2.5); its SIB10 and SIB11 are not part of the TS 103 720 profile.

Three layers define it. ETSI TS 103 720, the 5G Broadcast system specification maintained by 5G-MAG, profiles PWS support over the E-UTRAN Uu downlink. 3GPP TS 23.041 defines the Cell Broadcast Service message itself: its structure, message identifiers, serial numbers and data coding. 3GPP TS 36.331 defines how that message is encoded on the radio interface, as SystemInformationBlockType12, and what a UE does on receiving it.

5G-MAG maintains ETSI TS 103 720 and carries the public warning requirements into it, so feedback from implementing the alert chain in the reference tools feeds directly back into the specification. Contributions to this documentation are made through the 5G-MAG Standards repository.

At a glance
  • Three layers: ETSI TS 103 720 profiles PWS support over the E-UTRAN Uu downlink; 3GPP TS 23.041 defines the Cell Broadcast Service message; 3GPP TS 36.331 defines its radio encoding as SystemInformationBlockType12.
  • Carrier: the same free-to-air LTE-based broadcast carrier as linear TV and radio, with no SIM, subscription or return channel.
  • Maintenance: 5G-MAG maintains ETSI TS 103 720 and carries the public warning requirements into it.

Specifications​

SpecificationTitleLayerRel
ETSI TS 103 7205G Broadcast System for linear TV and radio services; LTE-based 5G terrestrial broadcast systemMaintained by 5G-MAG. PWS support, the delivery of warning messages via SIB broadcast on the E-UTRAN Uu downlink, is defined in v1.2.1 clause 5.15.3.3. Work towards v1.3.1 (aligning with 3GPP Release 18) adds further PWS-related improvements.System specification
TS 22.268Public Warning System (PWS) requirementsStage-1 PWS service requirements this whole page implements; SA1Service requirements9
TS 23.041Technical realization of Cell Broadcast Service (CBS)CBS message structure, message identifiers, serial numbers and data coding for ETWS and CMAS. Message identifier 0x1102 is the ETWS combined earthquake-and-tsunami identifier used by the reference transmitter.Warning message realisation
TS 29.168Cell Broadcast Centre interfaces with the Evolved Packet Core; Stage 3the CBC-to-EPC delivery path for the warning message before it reaches the radio interfaceWarning message realisation8
ETSI TS 102 900Emergency Communications (EMTEL); European Public Warning System (EU-ALERT) using the Cell Broadcast ServiceV1.4.1 (2023-06); profiles Cell Broadcast Service for EU-ALERT and national variants (e.g. NL-ALERT, UK-ALERT)Warning message realisation
OASIS CAP v1.2Common Alerting Protocolthe alert format received by the Cell Broadcast Centre at the CBE-CBC interface, which the CBC converts to a Cell Broadcast Service (CMAS) message (ETSI TS 103 720 V1.2.1 clauses 5.15.3.2 and 5.15.4); confirmed still current, no newer version publishedWarning message realisation
TS 36.331Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specificationDefines SystemInformationBlockType12 and the UE actions on receiving a warning-message SIB.Radio interface
TS 36.523-1Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); User Equipment (UE) conformance specification; Part 1: Protocol conformance specificationUE protocol conformance test cases; whether its ETWS/CMAS/SIB12-specific test-case content has been independently confirmed against the spec text itself is not established hereConformance testing8
TR 36.976Overall description of LTE-based 5G broadcastOverview16
note

Receiver behaviour for public warning, and the exact CBS feature coverage, depend on the version of ETSI TS 103 720 being implemented; work towards v1.3.1 adds PWS-related improvements. Confirm the current status against the repositories and the Kanban board before relying on it.

What the specifications state​

  • TS 22.268 V21.0.0, clause 1: "This Technical Specification defines the stage one description of the Public Warning System (PWS) Requirements." Its scope covers ETWS, CMAS, EU-ALERT and KPAS.
  • TS 23.041 V20.0.0, clause 1: "The present document describes the Cell Broadcast short message service (CBS) for GSM and UMTS." Table 9.4.1.2.2-1 assigns Message Identifier 1102 (hex): "ETWS CBS Message Identifier for earthquake and tsunami combined warning message."
  • TS 29.168 V19.0.0, clause 1: "The present document specifies the procedures and the SBc Application Part (SBc-AP) messages used on the SBc-AP interface between the Mobility Management Entity (MME) and the Cell Broadcast Centre (CBC), and between the Public Warning System – Inter Working Function (PWS-IWF) and the CBC."
  • TS 36.331 V19.4.0, clause 6.3.1: "The IE SystemInformationBlockType10 contains an ETWS primary notification." "The IE SystemInformationBlockType11 contains an ETWS secondary notification." "The IE SystemInformationBlockType12 contains a CMAS notification."
  • TR 36.976 V19.0.0, clause 1: "The present document provides an overview and overall description of the LTE-based 5G terrestrial broadcast comprising:" a free-to-air service and a radio network of MBMS-dedicated or FeMBMS/Unicast-mixed cells.
  • ETSI TS 103 720 V1.2.1, clause 5.15.3.3: "PWS warning messages shall be sent in the 5G Broadcast System via the Commercial Mobile Alert Service (CMAS) as described in this clause." and "Among the different types of SIB messages, SIB12 contains the CMAS notification for PWS." For PWS, "networks are only allowed to use identifiers between 4352 and 6399 inclusive."

Release by release​

From the 3GPP release descriptions (TR 21.915 V15.0.0, TR 21.916 V16.2.0, TR 21.917 V17.0.1, TR 21.919 V19.0.0); the full list with clauses is in Release history.

  • Release 15: the 5G System supports PWS through the CBC Function and AMF, and the NG interface gets a warning message transmission function (TR 21.915 clauses 5.5.2.2.7 and 5.5.3.5.3).
  • Release 16: ePWS adds ePWS-UE Message Identifiers and language-independent content (TR 21.916 clause 12.1); LTE_eMTC5 adds ETWS/CMAS notification in connected mode for non-Cat-M UEs (clause 7.3); LTE_terr_bcast produced TR 36.976 (clause 19.3.1).
  • Release 17: PWS over SNPN is supported (NG_RAN_PRN_enh, TR 21.917 clause 6.2.3.2).
  • Release 19: PWS_NTN adds PWS over satellite E-UTRAN and NG-RAN, ETWS geo-fencing and duplicate detection with a shared MCC (TR 21.919 clause 5.3.1); IoT_NTN_Ph3 adds NB-IoT ETWS and CMAS system information blocks (clause 5.1.3).
  • Release 20 (work plan of 28 September 2026): MLT-REQ, Stage 1 for Multilingual Template-based alerts (TS 22.268, UID 1130012, WID SP-261004); CPAS, Security Assurance Specification (UID 1110066, 90%, finish 12 December 2026; TS 23.304 in the work plan), with CPAS-REQ (TS 23.304) and CPAS-CT (TS 23.041). Details are in Release history. No Release 20 release description (TR 21.920) was available.
Sources for this page
  • 3GPP TS 22.268 V21.0.0, TS 23.041 V20.0.0, TS 29.168 V19.0.0, TS 36.331 V19.4.0 and TR 36.976 V19.0.0: the quotations under "What the specifications state".
  • ETSI TS 103 720 V1.2.1: clauses 4.2.5 and 5.15.3.3.
  • 3GPP TR 21.915 V15.0.0, TR 21.916 V16.2.0, TR 21.917 V17.0.1 and TR 21.919 V19.0.0: the release statements.
  • 3GPP work plan of 28 September 2026: the Release 20 work items.