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Cell Broadcast » History » Revision 6

Revision 5 (laforge, 08/19/2017 10:03 AM) → Revision 6/24 (laforge, 02/09/2018 08:20 PM)

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 h1. Cell Broadcast 

 Normally, all user plane data in GSM/GPRS networks are sent in point-to-point channels from the network to the user. Those are called "dedicated" radio channels whcih exist between the network and one given phone/subscriber at a time. 

 Cell Broadcast is an exception to that rule.    It permits user data (so-called SMS-CB data) to be broadcast by the network in a way that can be received by all phones in the coverage area of the given [[BTS]] simultaneously. 

 More high-level information can be found at https://en.wikipedia.org/wiki/Cell_Broadcast and the related specification is found at "3GPP TS 23.041 Technical realization of Cell Broadcast Service (CBS)":http://www.3gpp.org/ftp/Specs/html-info/23041.htm 

 h2. Use Cases 

 Cell Broadcast was used for various different use cases primarily in the 1990ies and early 2000s, including 
 * advertisement of the GPS position of the cell tower you're currently camping on 
 * advertisement of the calling codes of your current "home zone", i.e. a "lower cost short distance" call zone travelling with you as you roam around. 

 More recently, SMS-CB is seeing some uptake by various desaster warning systems, such as 
 * CMAS (Commercial Mobile Alert System), later renamed to WEA ("Wireless Emergency Alerts":https://en.wikipedia.org/wiki/Wireless_Emergency_Alerts) in the US. 
 * EU-Alert in the European union 
 * Messer Ishi (Rocket Alert) in Israel 
 * ETWS (Earthquake and Tsunami Warning System) in Japan 
 * KPAS (Korean Public Alert System) 

 h2. Osmocom Cell Broadcast support 

 * [[OsmoBTS:]] implements the "SMS BROADCAST COMMAND" Message in RSL according to Section 8.5.8 of 3GPP TS 08.58 *but not all hardware targets support this yet, see #1617. osmo-bts-sysmo and osmo-bts-octphy are fine.* 
 * [[OsmoNITB:]] and [[OsmoBSC:]] implement a VTY command @bts <0-255> smscb-command <1-4> HEXSTRING@ to send a given hex-formatted cell broadcast message to a specified BTS 

 !osmocom-cbs.png! 

 This is sufficient for manual transmission of cell-broadcast messages in a lab environment or in small networks.    The functionality has been developed and "used at the 31st annual CCC congress (31C3) to deliver spoofed _Presidential Level Alert_ messages":https://twitter.com/2b_as/status/549695235207737344/photo/1 

 h3. What's missing (for production operation in larger networks) 

 * mechanism to broadcast one (set of) cell broadcast messages from the BSC to multiple/all BTSs, rather than one BTS individually 
 * BTS reporting of current CBCH load 
 * BSC scheduler scheduling multiple alternating sets of CBCH messages based on the current CBCH load reported by BTS 
 * external interface from BSC to a Cell Broadcast Center (CBC), e.g. according to 3GPP TS 48.049 
 * an Osmocom implementation of the Cell Broadcast Center (OsmoCBC) which can manage and dsitribute messages to multiple BSCs and which has an external interface by which cell-broadcast can be entered into the network 

 h2. Message Structure 

 * Message has maximum 15 pages 
 * Each page is 82 bytes of data, resulting in 93 characters in GSM 7-bit default alphabet 
 * Messges are broadcast on logical channels (more like an address) 
 * Subscribers can activate/deactivate selective addresses 

 h2. Further Reading 

 * ITU-T SG2 (Standardization of CB Channels) 
 * 3GPP TS 23.041 Cell Broadcast 
 * ETSI 102 444 
 * "3GPP TS 22.268 PWS: Public Warning System (PWS) requirements":http://www.etsi.org/deliver/etsi_ts/122200_122299/122268/14.00.00_60/ts_122268v140000p.pdf 

 h3. EU-Alert 

 * ETSI/EMTEL TS 102 900 

 h3. CMAS 

 * ATIS/TIA Standards J-STD-100, 101, 102 

 h3. ETWS
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