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Cell Broadcast

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Public warning alerts using embedded Cell Broadcast feature on Android 7.1

Cell Broadcast/Cell Information (CB) is a method of sending messages to multiple mobile telephone users in a defined area at the same time. It is defined by the ETSI’s GSM committee and is part of the 2G, 3G, 4G LTE (telecommunication) and 5G standards. It is also known as Short Message Service-Cell Broadcast (SMS-CB).

Unlike Short Message Service-Point to Point (SMS-PP), Cell Broadcast is a one-to-many geographically limited messaging service.

History

Cell Broadcast messaging was first demonstrated in Paris in 1997. Some mobile operators use Cell Broadcast for communicating the area code of the antenna cell to the mobile user (via channel 050), for nationwide or citywide alerting, weather reports, mass messaging, location-based news, etc. Cell broadcast has been widely deployed since 2008 by major Asian, US, Canadian, South American and European network operators. Not all operators have the Cell Broadcast messaging function activated in their network yet, but most recent handsets support cell broadcast.

Service

One Cell Broadcast message can reach a large number of telephones at once. Cell Broadcast messages are directed to radio cells, rather than to a specific telephone. The latest generation of Cell Broadcast Systems (CBS) can send to as many as 500,000 cells in less than 10 seconds, reaching millions of mobile subscribers. A Cell Broadcast message is an unconfirmed push service, meaning that the originators of the messages do not know who has received the message, allowing for services based on anonymity. Cell Broadcast is compliant with the latest EU General Data Protection Regulation (GDPR) as mobile phone numbers are not required by CB. The originator (alerting authority) of the Cell Broadcast message can request the success rate of a message. In such a case the Cell Broadcast System will respond with the number of addressed cells and the number of cells that have broadcast the Cell broadcast (alert) message.

Technology

Cell Broadcast allows a text or binary message to be defined and distributed to all mobile terminals connected to a set of cells. A Cell Broadcast message page is composed of 82 octets, which, using the default character set, can encode 93 characters. Up to 15 of these pages may be concatenated to form a Cell Broadcast message (maximum length of one Cell broadcast message is therefore 1395 characters). Each page of such a CB message will have the same message identifier (indicating the source of the message), and the same serial number. Using this information, the mobile telephone is able to identify and ignore broadcasts of already received messages.

A Cell Broadcast Centre (CBC), a system which is the source of SMS-CB, is connected to a base station controller (BSC) in GSM networks, to a radio network controller (RNC) in UMTS networks, to a Mobility Management Entity (MME) in LTE (telecommunication) networks or to a core Access and Mobility management Function (AMF) in 5G networks.

  • The 2G-CBC (BSC) interface is described in 3GPP standard TS 48.049; however, non-standard implementations exist.
  • The 3G-CBC (RNC) interface is described in 3GPP standard TS 25.419.
  • The 4G-CBC and 5G-CBC (MME & AMF) interfaces are described in 3GPP standard TS 23.041.

A CBC sends SMS-CB messages, a list of cells where messages are to be broadcast, and the requested repetition rate and number of times they shall be broadcast to the BSC/RNC/MME/AMF. The BSC's/RNC's/MME/AMF responsibility is to deliver the SMS-CB messages to the base station (BTSs), NodeBs, ENodeBs and gNodeBs which handle the requested cells.

In GSM SMS-CB messages are broadcast over an air interface on a special signaling channel, Cell Broadcast Channel (CBCH). CBCH reuses one of signalling channels (SDCCH). There is only one CBCH in each cell in cellular network. GSM specification allows to send only one SMS-CB message page every 1.883 s in basic mode and another one in extended mode. However extended mode is optional in GSM thus neither networks nor mobile phones are required to support it, so the real throughput is only one message page each 1.883 s in basic mode.

Emergency communication system

Cell Broadcast is not affected by traffic load; therefore, it is usable during a disaster when load spikes of data (social media and mobile app), regular SMS and voice calls usage (mass call events) tend to significantly slowdown mobile networks, as multiple events have shown.

Wireless Emergency Alerts and Government alerts using Cell Broadcast are supported in recent models of mobile telephones. Smart phones have a configuration menu to enable/disable the receiving of Cell Broadcast messages.

Broadcast messages are used in most countries to send emergency alerts, using as input a CAP (Common Alerting Protocol) message or Wireless Emergency Alerts C-interface protocol, which has been specified jointly by the Alliance for Telecommunications Industry Solutions and the Telecommunications Industry Association.

Cell Broadcast adoption rate

A point of criticism in the past on Cell Broadcast was that there was no uniform user experience on all mobile devices in a country.

This limitation is since 2012 no longer present. In case a national civil defence organisation is adopting one of the Wireless Emergency Alerts standards, WEA - formerly known as CMAS in North America, EU-Alert in Europe, LAT-Alert in South America, Earthquake Tsunami Warning System in Japan, each subscriber in that country either making use of the home network or is roaming automatically makes use of the embedded Public warning Cell Broadcast feature present in every Android (operating system) and IOS mobile device.

In countries that have selected Cell Broadcast to transmit public warning messages, up to 70-85% of the population older than 12 year receive the public warning verification message within seconds after the government authorities have submitted the message see as an example Emergency Mobile Alert (New Zealand), Wireless Emergency Alerts (USA) and NL-Alert (Netherlands).

Public warning implementations

Many countries have implemented location-based alert systems based on cell broadcast. The alert messages to the population, already broadcast by various media, are relayed over the mobile network using cell broadcast.

An example of an actual Cell Broadcast Message on an Android smartphone, indicating a Tornado Warning in the covered area in the US.

Sources

  • "5G Americas White Paper Public Warning Systems in the Americas" (PDF). www.5gamericas.org. 5G Americas. July 2018.
  • "Mobile Network Public Warning Systems and the Rise of Cell-Broadcast" (PDF). www.gsma.com. GSMA. January 2013.
Wikimedia Commons has media related to GSM Standard.

References

  1. ^ "LT-Alert link".

Footnotes

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