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Public Warning Systems

Implementation Detail

See also: Developer Exchange.

In short
  • What this covers: the public warning chain of 5G Broadcast: the Cell Broadcast Centre (CBC), the broadcast transmitter, the MME and the alert receiver, judged against TS 23.041, TS 22.268, TS 29.168, ETSI TS 103 720, ETSI TS 102 900 (EU-Alert) and OASIS CAP v1.2.
  • What exists on main: a CBC that takes warnings as JSON, builds the CAP record and sends the SBc-AP Write-Replace-Warning and Stop-Warning requests; and a web page that shows the alerts a modem decodes. The transmitter and the MME have no alert code.
  • Source of this page: an audit of the main branch of each repository on 2026-10-21: every requirement split into the cases its clause defines, each case read against the code by one reader and then independently by a second, with a third reading where they disagreed. Cases that only a running system can settle are not shown.

What the Reference Tools implement​

The Emergency Alerts work sits on the 5G Broadcast transmit chain, which is LTE based. Four roles are audited:

  • Cell Broadcast Centre (rt-pws-cbc): receives a warning as JSON over HTTP, packs the headline and instruction as GSM 7-bit text, writes a CAP v1.2 record for each warning and sends the SBc-AP Write-Replace-Warning-Request and Stop-Warning-Request towards the MME. The interface to the cell broadcast entity is JSON, not CAP, and the CBC decodes nothing that comes back.
  • Transmitter (rt-mbms-tx, rt-mbms-tx-for-qrd-and-crd): the srsRAN eNB builds the MBMS system information only. It has no handler for SIB10 to SIB12 or for ETWS and CMAS paging indications.
  • MME (srsepc in the two transmitter repositories): handles S1 setup and a few S1AP messages. It has no SBc-AP interface towards a CBC.
  • Receiver (rt-mbms-application): a web page that polls the modem and shows the current CMAS and ETWS alerts with a history, times and repeat count. Decoding, duplicate handling and message identification are in the modem, which is outside this audit.

What this means for a warning end to end: the CBC can produce and send a request, but nothing on main of the transmitter or the MME carries it on to the air interface.

  • Needs fix in the CBC:
    • Warning content is sent as one unpaged GSM 7-bit string, not as CBS pages of 82 octets with a length octet and a language each.
    • The serial number is a plain counter, without geographical scope, message code and update number.
    • The CAP <sent> value carries milliseconds and a +00:00 time zone, where CAP requires whole seconds and -00:00.
    • A polygon is accepted with three vertices and its closure is not checked.
    • The language is fixed and characters outside GSM 7-bit become ?.
    • The default repetition period is 4096, above the maximum of 4095.
    • A success answer is returned whatever the MME replies.
  • Not implemented in the CBC: paging, 8-bit and compressed content, the 5GS and PWS-IWF paths, and the SBc-AP error handling.
  • Not implemented in the receiver: opt-in and opt-out, the dedicated alerting indication, location checks, URL and call actions, and dismissal of an alert.

Implementation status​

Open a feature, then a requirement, to see each case and why. Filter by component and release.

  • 5G Broadcast for Emergency Alerts.
  • CBC (Cell Broadcast Centre and alert origination): rt-pws-cbc.
  • MME (MME (SBc-AP towards the CBC)): rt-mbms-tx-for-qrd-and-crd, rt-mbms-tx.
  • Transmitter (5G Broadcast Transmitter (E-UTRAN warning system information)): rt-mbms-tx-for-qrd-and-crd, rt-mbms-tx.
  • Receiver (5G Broadcast Receiver (PWS Client)): rt-mbms-application.
  • Source: code read against every statement of the specifications on the project page; statements a component cannot meet by construction marked absent by group, 2026-10-21.
  • Not shown: 7 further cases (a specification or code outside the audit that could not be read).
3GPP release
138 of 879 implemented · 52 differ · 689 absentcases, over 265 requirements

✓ Implemented≠ Differs from the specification– Absent? Specification inconsistent: its text and its OpenAPI or tables disagreei Noted: observed, not a verdict against a clause

The CBS message model on the transmit side74 of 301 implemented · 18 differ · 209 absent
Transmit and receive roles21 of 132 implemented · 16 differ · 95 absent
The complete public warning chain34 of 380 implemented · 16 differ · 330 absent
How it works8 of 47 implemented · 2 differ · 37 absent
General1 of 19 implemented · 18 absent
Full audit for members

The full audit, with the code behind each verdict, is available to 5G-MAG members through Developer Tools.

Become a member · Request access

Used with other projects​

  • 5G Broadcast: the transmitter and the MBMS application repositories are shared with Media delivery over 5G Broadcast; this page covers only their alert behaviour.
note

Refer to the 5G Broadcast - Emergency Alerts repositories on GitHub to use or contribute to these Reference Tools. See How to Contribute for the process.