OsmoBTS - OsmocomBB emulation project

Dominiq T chester.mino at gmail.com
Sat Apr 11 15:20:43 UTC 2015


Hi Mike,

Thanks for your advice.


> 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.

- for the openbts, i found UDP channel on 5944 <--->5934 ports. But in case
of the osmo-bts-trx i did not found anything. Even with openBTS i could see
some "activity" of the PCU . I.e. while i started my app with OpenBTS, i
could see at least:

<0001> pcu_l1_if.cpp:330 BTS available
<0001> pcu_l1_if.cpp:80 Sending activate request: trx=0 ts=6
<0001> pcu_l1_if.cpp:456 PDCH: trx=0 ts=6
<0001> pcu_l1_if.cpp:80 Sending activate request: trx=0 ts=7
<0001> pcu_l1_if.cpp:456 PDCH: trx=0 ts=7

but with trx no activity at all. I am doing something wrong ? Do I have
change config somehow ?


>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.

- I think i can do it like this: As a "transmit" interface BTS -> osmocomBB
i want to use GSMTAP feature. I thing there is suffient support of this
protocol for my needs. The biggest issue i can see is, how to handle
receive messages GSMTAP messages on my eBTS. I have idea to transform these
messages into l1sap readable format, and send them to l1sap_up() function
(which, if I am not mistaken , is a single point for trasnfer primitives
from the TRX - please correct me). I have currently no idea what willl
happen, and if its even possible to "jump over" the lower parts of the
code...

Thanks.

Dominik






2015-04-07 18:10 GMT+02:00 Mike McTernan (wavemobile) <
mike.mcternan at wavemobile.com>:

> 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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