Project

General

Profile

Cell Broadcast » History » Version 20

laforge, 09/13/2019 08:25 PM
ladder diagram

1 1 laforge
h1. Cell Broadcast
2 7 fixeria
3
{{>toc}}
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.
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 16 laforge
*NOTE: In 3G/UMTS networks, Cell Broadcast is called [[Service_Area_Broadcast]] and we have a dedicated wiki page for it.*
12
13 20 laforge
h2. Cell Broadcast Architecture
14
15
h3. Network Diagram
16
17
This Network diagram shows the relevant elements in the GSM network, including their interconnection.
18
19 19 laforge
{{graphviz_link()
20
digraph G {
21
  BTS0 [label="BTS"];
22
  BTS1 [label="BTS"];
23
  BTS10 [label="BTS"];
24
  BTS11 [label="BTS"];
25
  BSC1 [label="BSC"];
26
27
  User -> CBC [label="proprietaty"];
28
  CBC -> BSC [label="CBSP"];
29
  CBC -> BSC1 [label="CBSP"];
30
  BSC -> BTS0 [label="RSL"];
31
  BSC -> BTS1 [label="RSL"];
32
  BSC1 -> BTS10 [label="RSL"];
33
  BSC1 -> BTS11 [label="RSL"];
34
  BTS0 -> MS [label="CBCH"];
35
}
36
}}
37 20 laforge
38
h3. Ladder Diagram
39
40
This ladder diagram shows the propagation / flow of messages across the Cell Broadcast enabled network.
41
42
!osmodevcon2019-cell_broadcast__2.png!
43 19 laforge
44 2 laforge
h2. Use Cases
45 1 laforge
46 2 laforge
Cell Broadcast was used for various different use cases primarily in the 1990ies and early 2000s, including
47
* advertisement of the GPS position of the cell tower you're currently camping on
48
* 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.
49
50
More recently, SMS-CB is seeing some uptake by various desaster warning systems, such as
51
* CMAS (Commercial Mobile Alert System), later renamed to WEA ("Wireless Emergency Alerts":https://en.wikipedia.org/wiki/Wireless_Emergency_Alerts) in the US.
52
* EU-Alert in the European union
53
* Messer Ishi (Rocket Alert) in Israel
54
* ETWS (Earthquake and Tsunami Warning System) in Japan
55
* KPAS (Korean Public Alert System)
56
57 10 laforge
h2. Osmocom Cell Broadcast support
58 1 laforge
59 18 laforge
* [[OsmoBTS:]] implements
60
** the CBCH channel (both BASIC and EXTENDED) in the SDCCH/4 and SDCCH/8
61
** the "SMS BROADCAST COMMAND" Message in RSL according to Section 8.5.8 of 3GPP TS 08.58
62
** the "CBCH LOAD INDICATION" Message in RSL, which allows the BSC to perform flow control of CBCH messages
63
* [[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 (this is more a hack for manual testing)
64 1 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
65 18 laforge
* [[OsmoBSC:]] implements
66
** the scheduling / allocation of CBCH resources in presence of possibly many SMSCB messages, taking into account their message size, repetition period, duration
67
** the CBSP protocol according to 3GPP TS 48.049 for interaction with a CBC
68
** CBCH flow control based on incoming CBCH LOAD INDICATION via RSL from BTSs
69
** transmission of SMSCB using SMS BROADCAST COMMAND via RSL to BTSs
70
* [[OsmoCBC:]] implements
71
* FIXME
72 19 laforge
73 2 laforge
74 1 laforge
75
76
h3. How to test/use it
77
78 18 laforge
h4. Using recent OsmoBSC and OsmoCBC
79
80
h5. make sure your related BTS is configured to use a channel combination with CBCH
81
82
For using a combined CCCH with SDCCH/4 and CBCH you can use the following example snippet as part of osmo-bsc.cfg:
83
84
<pre>
85
network
86
 bts 0
87
  trx 0
88
   timeslot 0
89
    phys_chan_config CCCH+SDCCH4+CBCH
90
</pre>
91
92
h5. Setting up OsmoCBC
93
94
FIXME.
95
96
h4. Using the "manual hack" via BSC/NITB VTY command
97
98
!osmocom-cbs.png!
99
100
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
101
102 10 laforge
You need to perform two steps:
103
104 18 laforge
h5. make sure your related BTS is configured to use a channel combination with CBCH
105 10 laforge
106
For using a combined CCCH with SDCCH/4 and CBCH you can use the following example snippet as part of osmo-bsc.cfg:
107
108
<pre>
109
network
110 1 laforge
 bts 0
111 10 laforge
  trx 0
112
   timeslot 0
113
    phys_chan_config CCCH+SDCCH4+CBCH
114
</pre>
115
116 18 laforge
h5. telnet to osmo-bsc at port 4242, and enter something like
117 1 laforge
118
<pre>
119
enable
120
bts 0 smscb-command 1 001000320f1141660c344dd3cba09a0c
121
</pre>
122 10 laforge
123 1 laforge
where "1" is the number of blocks required (each 22 bytes need one block)
124 10 laforge
and the hex-dump at the end is the encoded GSM 04.12 message to be broadcast.
125
126
127 3 laforge
128 2 laforge
h2. Message Structure
129
130
* Message has maximum 15 pages
131
* Each page is 82 bytes of data, resulting in 93 characters in GSM 7-bit default alphabet
132
* Messges are broadcast on logical channels (more like an address)
133
* Subscribers can activate/deactivate selective addresses
134
135
h2. Further Reading
136
137
* ITU-T SG2 (Standardization of CB Channels)
138
* ETSI 102 444
139 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
140
* "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
141 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
142 1 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
143 14 laforge
* "Whitepaper on Displaying Cell Broadcast":https://www.one2many.eu/assets/files/19_displaying-cb-messages.pdf
144 2 laforge
145
h3. EU-Alert
146
147 13 laforge
* "ETSI/EMTEL TS 102 900":https://www.etsi.org/deliver/etsi_ts/102900_102999/102900/01.01.01_60/ts_102900v010101p.pdf
148 2 laforge
149
h3. CMAS
150
151 12 laforge
* "FCC 08-99: First Report and Order":https://www.one2many.eu/assets/files/16_first-report-and-order.pdf
152
* "FCC 08-164: Second Report and Order":https://www.one2many.eu/assets/files/17_second-report-and-order.pdf
153
* "FCC 08-184: Third Report and Order":https://www.one2many.eu/assets/files/18_third-report-and-order.pdf
154 15 laforge
* "ATIS/TIA Standard J-STD-100 (Mobile Device Behavior)":https://global.ihs.com/doc_detail.cfm?&document_name=TIA%20J-STD-100
155
* "ATIS/TIA Standard J-STD-101 (Federal Alert Gateway to CMSP Gateway Interface Spec)":https://global.ihs.com/doc_detail.cfm?&document_name=TIA%20J-STD-101
156
* "ATIS/TIA Standard J-STD-102 (Federal Alert Gateway to CMSP Gateway Interface Test Spec)":https://global.ihs.com/doc_detail.cfm?&document_name=TIA%20J-STD-102
157 14 laforge
* "ATIS 0700006 eWEA via GSM/UMTS Cell Broadcast Service Spec":https://global.ihs.com/doc_detail.cfm?document_name=ATIS%200700006
158
* "ATIS 0700007 Implementation Guidelines and Best Practises for GSM/UMTS Cell Broadcast Service":https://global.ihs.com/doc_detail.cfm?document_name=ATIS%200700007
159
* "ATIS 0700008 Cell Broadcast Entity (CBE)-to-Cell Broadcast Center (CBC) Interface Specification":https://global.ihs.com/doc_detail.cfm?document_name=ATIS%200700008
160
* "ATIS 0700010 Enhanced Wireless Emergency Alert (eWEA) via EPS Public Warning System Specification":https://global.ihs.com/doc_detail.cfm?document_name=ATIS%200700010
161 2 laforge
162
h3. ETWS
163 11 laforge
164
* "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
165
* various modifications to TS 23.038, 23.401, 25.304, 25.331, see http://www.3gpp.org/DynaReport/WiCr--370051.htm
166 17 laforge
167
h2. Cell Broadcast in 3G/UMTS
168
169
See [[Service_Area_Broadcast]]
170
171
h3. Cell Broadcast in 4G/LTE
172
173
h4. SBc interface between CBC and MME
174
175
The interface is based on a ASN.1 based protocol called SBc-AP which is specified in "3GPP TS 29.168":https://www.etsi.org/deliver/etsi_ts/129100_129199/129168/15.01.00_60/ts_129168v150100p.pdf
176
177
The protocol operates over SCTP. Connections are initiated by the CBC to the MME, and the MME listens for SBcAP connections on SCTP port 29168.
Add picture from clipboard (Maximum size: 48.8 MB)