Project

General

Profile

Cell Broadcast » History » Version 4

laforge, 05/29/2017 06:37 PM

1 1 laforge
{{>toc}}
2
3
h1. Cell Broadcast
4
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.
6
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.
8
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
10
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
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.
16
17
More recently, SMS-CB is seeing some uptake by various desaster warning systems, such as
18
* CMAS (Commercial Mobile Alert System), later renamed to WEA ("Wireless Emergency Alerts":https://en.wikipedia.org/wiki/Wireless_Emergency_Alerts) in the US.
19
* EU-Alert in the European union
20
* Messer Ishi (Rocket Alert) in Israel
21
* ETWS (Earthquake and Tsunami Warning System) in Japan
22
* KPAS (Korean Public Alert System)
23
24 1 laforge
h2. Osmocom Cell Broadcast support
25
26
* [[OsmoBTS:]] implements the "SMS BROADCAST COMMAND" Message in RSL according to Section 8.5.8 of 3GPP TS 08.58
27
* [[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
29 4 laforge
!osmocom-cbs.png!
30
31 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
32 1 laforge
33
h3. What's missing (for production operation in larger networks)
34
35
* mechanism to broadcast one (set of) cell broadcast messages from the BSC to multiple/all BTSs, rather than one BTS individually
36
* BTS reporting of current CBCH load
37
* BSC scheduler scheduling multiple alternating sets of CBCH messages based on the current CBCH load reported by BTS
38 2 laforge
* external interface from BSC to a Cell Broadcast Center (CBC), e.g. according to 3GPP TS 48.049
39 3 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
40
41 2 laforge
h2. Message Structure
42
43
* Message has maximum 15 pages
44
* Each page is 82 bytes of data, resulting in 93 characters in GSM 7-bit default alphabet
45
* Messges are broadcast on logical channels (more like an address)
46
* Subscribers can activate/deactivate selective addresses
47
48
h2. Further Reading
49
50
* ITU-T SG2 (Standardization of CB Channels)
51
* 3GPP TS 23.041 Cell Broadcast
52
* ETSI 102 444
53
* "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
54
55
h3. EU-Alert
56
57
* ETSI/EMTEL TS 102 900
58
59
h3. CMAS
60
61
* ATIS/TIA Standards J-STD-100, 101, 102
62
63
h3. ETWS
Add picture from clipboard (Maximum size: 48.8 MB)