Cell Broadcast » History » Revision 8
Revision 7 (fixeria, 07/26/2018 04:51 PM) → Revision 8/25 (laforge, 09/06/2018 12:42 PM)
h1. Cell Broadcast {{>toc}} 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 ** you (obviously) first need to enable a timeslot/channel combination on the BTS that actually includes a CBCH, i.e. ccch+sdcch4+cbch or sdcch8+cbch !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