Cell Broadcast » History » Version 11
laforge, 09/29/2018 09:13 AM
1 | 1 | laforge | h1. Cell Broadcast |
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2 | 7 | fixeria | |
3 | {{>toc}} |
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4 | 1 | laforge | |
5 | 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. |
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7 | 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. |
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9 | 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 |
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11 | 2 | laforge | h2. Use Cases |
12 | 1 | laforge | |
13 | 2 | laforge | Cell Broadcast was used for various different use cases primarily in the 1990ies and early 2000s, including |
14 | * advertisement of the GPS position of the cell tower you're currently camping on |
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15 | * 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. |
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17 | More recently, SMS-CB is seeing some uptake by various desaster warning systems, such as |
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18 | * CMAS (Commercial Mobile Alert System), later renamed to WEA ("Wireless Emergency Alerts":https://en.wikipedia.org/wiki/Wireless_Emergency_Alerts) in the US. |
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19 | * EU-Alert in the European union |
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20 | * Messer Ishi (Rocket Alert) in Israel |
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21 | * ETWS (Earthquake and Tsunami Warning System) in Japan |
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22 | * KPAS (Korean Public Alert System) |
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24 | 10 | laforge | h2. Osmocom Cell Broadcast support |
25 | 1 | laforge | |
26 | 6 | laforge | * [[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.* |
27 | 1 | laforge | * [[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 |
28 | 8 | laforge | ** 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 |
29 | 1 | laforge | |
30 | 4 | laforge | !osmocom-cbs.png! |
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32 | 2 | laforge | 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 |
33 | 1 | laforge | |
34 | 10 | laforge | h3. How to test/use it |
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36 | You need to perform two steps: |
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38 | h4. make sure your related BTS is configured to use a channel combination with CBCH |
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40 | For using a combined CCCH with SDCCH/4 and CBCH you can use the following example snippet as part of osmo-bsc.cfg: |
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41 | |||
42 | <pre> |
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43 | network |
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44 | bts 0 |
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45 | trx 0 |
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46 | timeslot 0 |
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47 | phys_chan_config CCCH+SDCCH4+CBCH |
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48 | </pre> |
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49 | |||
50 | h4. telnet to osmo-bsc at port 4242, and enter something like |
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51 | |||
52 | <pre> |
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53 | enable |
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54 | bts 0 smscb-command 1 001000320f1141660c344dd3cba09a0c |
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55 | </pre> |
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56 | |||
57 | where "1" is the number of blocks required (each 22 bytes need one block) |
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58 | and the hex-dump at the end is the encoded GSM 04.12 message to be broadcast. |
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59 | |||
60 | 1 | laforge | h3. What's missing (for production operation in larger networks) |
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62 | * mechanism to broadcast one (set of) cell broadcast messages from the BSC to multiple/all BTSs, rather than one BTS individually |
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63 | * BTS reporting of current CBCH load |
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64 | * BSC scheduler scheduling multiple alternating sets of CBCH messages based on the current CBCH load reported by BTS |
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65 | 10 | laforge | * external interface from BSC to a Cell Broadcast Center (CBC), e.g. according to 3GPP TS 48.049 (CBSP) |
66 | 1 | laforge | * 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 |
67 | 10 | laforge | |
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70 | 3 | laforge | |
71 | 2 | laforge | h2. Message Structure |
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73 | * Message has maximum 15 pages |
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74 | * Each page is 82 bytes of data, resulting in 93 characters in GSM 7-bit default alphabet |
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75 | * Messges are broadcast on logical channels (more like an address) |
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76 | * Subscribers can activate/deactivate selective addresses |
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78 | h2. Further Reading |
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79 | |||
80 | * ITU-T SG2 (Standardization of CB Channels) |
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81 | * 3GPP TS 23.041 Cell Broadcast |
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82 | * ETSI 102 444 |
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83 | 9 | laforge | * "3GPP TS 23.041 GSM: Technical realization of Cell Broadcast Service (CBS)":https://www.etsi.org/deliver/etsi_ts/123000_123099/123041/15.02.00_60/ts_123041v150200p.pdf |
84 | * "3GPP TS 48.049 GSM: Baste Station Controller - Cell Broadcast Centre (BSC-CBC) interface specification; Cell Broadcast Service Protocol (CBSP)":https://www.etsi.org/deliver/etsi_ts/148000_148099/148049/15.00.00_60/ts_148049v150000p.pdf |
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85 | 2 | laforge | * "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 |
86 | 9 | laforge | * "3GPP TS 44.012 GSM: Short Message Service Cell Broadcast (SMSCB) support on the mobile radio interface":https://www.etsi.org/deliver/etsi_ts/144000_144099/144012/15.00.00_60/ts_144012v150000p.pdf |
87 | 2 | laforge | |
88 | h3. EU-Alert |
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89 | |||
90 | * ETSI/EMTEL TS 102 900 |
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91 | |||
92 | h3. CMAS |
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93 | |||
94 | * ATIS/TIA Standards J-STD-100, 101, 102 |
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96 | h3. ETWS |
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97 | 11 | laforge | |
98 | * "3GPP TS 22.168: ETWS Requirements Stage 1":https://www.etsi.org/deliver/etsi_ts/122100_122199/122168/08.03.00_60/ts_122168v080300p.pdf |
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99 | * various modifications to TS 23.038, 23.401, 25.304, 25.331, see http://www.3gpp.org/DynaReport/WiCr--370051.htm |