Cell Broadcast

Cell Broadcast (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 3GPP 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).

Public warning alerts using embedded Cell Broadcast feature on Android 7.1

Unlike Short Message Service-Point to Point (SMS-PP), Cell Broadcast is a one-to-many geo-targeted and geo-fenced messaging service.

History

Cell Broadcast messaging was first demonstrated in Paris in 1997. Some mobile operators used 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 of the currently used 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 the whole mobile network (e.g. 1,000,000 cells) in less than 10 seconds, reaching millions of mobile subscribers at the same time. 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

The maximum length of a cell broadcast message is 1395 characters. The CB message parameters contain the broadcasting schedule. If the start-time is left open, the CBC system will assume an immediate start, which will be the case for Public Warning messages. If the end-time is left open, the message will be repeated indefinitely. A subsequent cancel message shall be used to stop this message. The repetition rate can be set between 2 seconds and to values beyond 30 minutes. Each repeated 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 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 (hence maximum length of one Cell broadcast message is therefore 1395 characters).

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 technical implementation of the cell broadcast service is described in the 3GPP specification TS 23.041 [1]

  • 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 (MME) interface is described in 3GPP standard TS 29.168.
  • The 5G-CBC (AMF) interface is described in 3GPP standard TS 29.518.

A CBC sends 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 CB messages to the base station (BTSs), NodeBs, ENodeBs and gNodeBs which handle the requested cells.

Emergency communication system

Cell Broadcast is not affected by traffic load; therefore, it is very suitable 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 congest mobile networks, as multiple events have shown.

Wireless Emergency Alerts and Government alerts using Cell Broadcast are supported in all models of mobile telephones. Smart phones have a configuration menu that offer opt-out capabilities for certain public warning severity levels.

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

Advantages of using Cell Broadcast for Public warning are:

  • Sending out a Cell Broadcast message to a few or millions of people take less than 10 seconds
  • Cell Broadcast has a unique and dedicated ringtone and vibration
  • Only an authorized authority and the serving mobile network are able to send out the Cell Broadcast messages
  • 99% of all handsets used today support Cell Broadcast
  • Cell Broadcast supports per CB-message a maximum message length of 1395 characters in Latin and 615 characters in Universal Coded Character Set (UCS-2) encoding in order to support e.g. Arabic, Chinese alphabet, Urdu, Greek alphabet.
  • Cell Broadcast supports multiple languages
  • Cell Broadcast supports the use of URLs and Web-links in the alert message
  • Cell Broadcast supports Device Based Geo-Fencing
  • Cell Broadcast supports the update within seconds of existing alert messages due to changing hazard situations
  • Cell Broadcast supports the mechanism to inform and instruct people within seconds in the adjacent hazard areas
  • Cell Broadcast is able to reach all mobile subscribers including roaming subscribers (in their own language)
  • Cell Broadcast is not affected by mobile network congestion
  • Cell Broadcast is not affected by access class baring and or SIM class baring
  • Cell Broadcast is not affected by any data protection constraints as no personal data (subscriber identity or MSISDN) is required and used to deliver the message.
  • Cell Broadcast can be used to address people present in an individual cell sector or large polygons covering a complete city or country.
  • Cell Broadcast messages can be updated as incident conditions change during an event at the end of an event an all-clear can be given.
  • Cell Broadcast is suitable for monthly or half yearly national public warning awareness tests
  • Cell Broadcast enablement in the mobile network has no influence on the battery life of mobile devices

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 99% of the handsets receive the cell broadcast message reaching between 85-95% of the entire population as not all people have a mobile phone within seconds after the government authorities have submitted the message see as examples Emergency Mobile Alert (New Zealand), Wireless Emergency Alerts (USA) and NL-Alert (Netherlands).

Public warning implementations

Many countries and regions 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.

Countries in the process of implementing Cell Broadcast for the national public warning system

The following countries and regions have selected Cell Broadcast to use for their national public warning system but are currently in the process of implementing.

Countries trialing Cell Broadcast for public warning purposes

The government of the United Kingdom established a project to evaluate options for a National Alerting Service in 2013, conducted trials in 2014[5]. The project stopped in 2015. In 2018 the Cabinet Office commissioned a discovery report to assess the state of UK networks, review international developments with mobile alerting and the steps required to implement a service in the UK[6]. In 2019, The Environment Agency together with Fujitsu, the Mobile Operator EE and the University of Hull explored the potential use of Cell Broadcast as an alerting channel for severe flooding. In January 2019 a Cell Broadcast message was successfully sent from the Flood Warning System over the 4G network in EE's test lab to a number of mobile devices. During 2019 the Environment Agency commissioned a survey to assess public responses to the use of Cell Broadcast messages and in November 2019 a workshop was held at the University of Hull to assess behavioural responses to Cell Broadcast messages. The results of this workshop were made available publicly [7].

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.
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References
  1. Technical realization of Cell Broadcast Service (CBS)
  2. "Lithuania Public Warning and Information System". Archived from the original on 2019-08-27. Retrieved 2019-01-13.
  3. "Taiwan Public Warning Cell Broadcast Service".
  4. "Hurtigere mobilvarsling til borgere ved kriser" [Faster mobile warnings to citizens during crises] (in Danish). Ministry of Defence. 2020-08-03. Retrieved 2020-08-03.
  5. "Public emergency alerts: mobile alerting trials". GOV.UK. Retrieved 2020-06-01.
  6. "Mobile Alerting - Discovery - Digital Marketplace". www.digitalmarketplace.service.gov.uk. Retrieved 2020-06-01.
  7. "Emergency Alerting in England". Google Drive. Retrieved 2020-06-01.

Footnotes
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