PageOutline = layer23 =

The ''layer23'' program is the playground we use for developing the GSM Protocol layers 2 and 3 (GSM TS 04.05, 04.06, 04.08)

Using the layer23 program, you can: * Connect to /tmp/osmocom_l2 socket created by [wiki:osmocon] to exchange data from [wiki:L1A_L23_Interface]. * Receive GSM Layer1 frames. * Dump received GSM Layer1 frames and print some analysis. * Send the Layer1 frames as [wiki:GSMTAP] packets to wireshark (see [wiki:WiresharkIntegration]) * forward the Layer1 frames to the Layer2 / LAPDm implementation inside layer23 * forward them from Layer2 into Layer3 code inside layer23. * receive outgoing frames from Layer3 * process them through layer2 * send them as uplink frames to [wiki:GSMTAP] * send them to the Layer1 on the phone

The ''layer23'' program is used in combination with the [wiki:layer1.bin] firmware.

=== Usage === {{{
./layer23 -a 871 -i 127.0.0.1
}}}

where {{{-a 871}}} indicates the GSM ARFCN to which layer1 shall tune, and {{{-i 127.0.0.1}}} indicates the IP address
to which the [wiki:GSMTAP] messages are to be sent.

This will connect to the [wiki:osmocon] application and will receive GSM Layer1 frames.
The receiving is done in the src/main.c and the frames will be passed to src/l1ctl.c,
from there into src/lapdm.c and finally into src/layer3.c

The output of the layer23 application is currently looking like this: {{{
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
SI3 on wrong TC
Found sync burst: SNR: 16384 TDMA: (0003/15/46) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/25/05) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/09/15) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/19/25) bsic: 49
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
SI4 on wrong TC
Found sync burst: SNR: 16384 TDMA: (0003/14/46) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/24/05) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/08/15) bsic: 49
Found sync burst: SNR: 16384 TDMA: (0003/18/25) bsic: 49
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
SI13 on wrong TC
}}}

=== Goals ===

The goal for the layer2+ application is to turn it into a complete GSM Stack for Mobile stations.
This will include handling of GSM Layer2 (LAPDm, GSM 04.06), GSM Layer3 (GSM 04.08).