OsmoBTS - OsmocomBB emulation project

Mike McTernan (wavemobile) mike.mcternan at wavemobile.com
Tue Apr 7 16:15:49 UTC 2015


Hi Dominiq,

> I am trying to remove l1 on both sides and connect OsmoBTS with BB application via simple unix sockets. 
...
> Currently I am able to handle messages between BTS and TRX driver on clock and control ports
...
> The thing is that I need to send to BB phone (layer23) messages in structures from gsm_04_08.h (i.e. gsm48_system_information_type_3). 

> I am not sure if I will be able to get needed from the messages coming on the data port 5702. 
 
You are correct. The data port UDP messages carry burst data - that is data after convolutional encoding and interleaving as well as training sequence insertion, padding etc...  You would have to very inefficiently decode all this again to retrieve the CSN data bits you seek, though you could then stimulate the timing advance and power control loops.

> I found, that PCU creates unix socket on “/tmp/pcu_bts” , but only in case sysmoBTS is in use (please correct me if I am wrong),

For non-sysmoBTS there is a different socket, TCP or UDP - I forget, but that's why you don't see the SEQ_PACKET Unix socket in /tmp for the other config.  Check sysmo_sock.cpp vs openbts_sock.cpp.

> So basically I need somehow to get this message structures on my custom l1 BB interface. 
> Do you have any idea how to do this ? 
 
I'm no expert, but depending on your ultimate goal you may have some luck pulling them out of the GSMTAP interface.  You can view this using Wireshark to quickly see if it is enough.  Check the docs or source on how to set this up and view it.

Alternatively, using the trx branch, you could try implementing a custom l1.  Check around the bts_model/l1sap code for the software interface (which is shared between the code in osmo-bts-sysmo and osmo-bts-trx).  That's probably a fair bit of work but gives you a lot of flexibility.

Kind Regards,

Mike


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