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Ccch scan » History » Version 2

Anonymous, 02/19/2016 10:49 PM
Copied from /trac/wiki/layer23 version 8; this reflects the name change in the current code.

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{{>toc}}
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h1. ccch_scan
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The _ccch_scan_ program (formerly layer23) is the playground we use for developing the GSM Protocol layers 2 and 3 (GSM TS 04.05, 04.06, 04.08)
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Using the ccch_scan program, you can:
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** Connect to /tmp/osmocom_l2 socket created by [[osmocon]] to exchange data from [[L1A_L23_Interface]].
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** Receive GSM Layer1 frames.
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*** Dump received GSM Layer1 frames and print some analysis.
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*** Send the Layer1 frames as [[GSMTAP]] packets to wireshark (see [[WiresharkIntegration]])
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*** forward the Layer1 frames to the Layer2 / LAPDm implementation inside ccch_scan
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*** forward them from Layer2 into Layer3 code inside ccch_scan.
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** receive outgoing frames from Layer3
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*** process them through layer2
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*** send them as uplink frames to [[GSMTAP]]
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*** send them to the Layer1 on the phone
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The _ccch_scan_ program is used in combination with the [[layer1bin]] firmware.
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h3. Usage
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<pre>
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./ccch_scan -a 871 -i 127.0.0.1
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</pre>
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<pre>
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to which the [[GSMTAP]] messages are to be sent.
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This will connect to the [[osmocon]] application and will receive GSM Layer1 frames. 
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The receiving is done in the src/main.c and the frames will be passed to src/l1ctl.c,
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from there into src/lapdm.c and finally into src/layer3.c
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The output of the ccch_scan application is currently looking like this:
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<pre>
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Found CCCH burst(s): TDMA: (0003/08/39) tc:3 49 06 1b 3b 80 62 f2 20 01 3a c8 07 0a 15 65 04 b9 00 00 80 00 02 1b  si: 0x1b
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        SI3 on wrong TC
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Found sync burst: SNR: 16384 TDMA: (0003/15/46) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/25/05) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/09/15) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/19/25) bsic: 49
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Found CCCH burst(s): TDMA: (0003/07/39) tc:4 31 06 1c 62 f2 20 01 3a 65 04 b9 00 00 80 00 53 2b 2b 2b 2b 2b 2b 2b  si: 0x1c
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        SI4 on wrong TC
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Found sync burst: SNR: 16384 TDMA: (0003/14/46) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/24/05) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/08/15) bsic: 49
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Found sync burst: SNR: 16384 TDMA: (0003/18/25) bsic: 49
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Found CCCH burst(s): TDMA: (0003/06/39) tc:5 01 06 00 b0 00 58 47 eb 4a 92 53 40 62 84 eb 2b 2b 2b 2b 2b 2b 2b 2b  si: 0x0
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        SI13 on wrong TC
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</pre>
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