wireshark, viewing Abis communication

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Nordin bouchtaoui at gmail.com
Fri Jul 31 08:30:05 UTC 2009


> Can you please indicate which OML messages (packet number in your pcap) are not
> decoded well?

I think all OML messages. The ipaccess-specific and RSL are decoded well.
But I run Wireshark under windows, so I guess it's not provided with 
your latest patches.

> Also, I think it should be pretty straight forward to look at the 12.21 spec and extend the
> packet-gsm_abis_oml.c code in wireshark.  We need more people working on this
> than just me ;)
>   

Yes, it is straightforward. I really do my best to get some time free to 
extend the decodings for Wireshark and I really like to cooperate to 
help the project.

> Why would you need that?  If you run your own network, then you know the
> neighbouring cells at the BSC and you can fill it from there.
>   

Well, if you reject a MS, it will be left with an empty BA list, so I 
guess it starts scanning all over again for a BTS to register. But if 
the MS has a BA list, it can, after it is rejected, reselect for antoher 
bts/arfcn. So in this way, I can accept my own MS and reject others, 
without disturbing the others. And I can play with my MS and see how our 
bsc behaves and, who knows, find a security leak?

> If you want to operate a rouge BTS for security research or in imsi-catcher
> style applications, then you probably don't want to fill neighbor cell
> information in the syste info messages, since that would tell the phones
> how to easily get away from your rogue cell (which you typically don't want)
>   

For me it's more important to learn understanding the GSM technique, how 
to read a documentation, how to program in Linux, how to develope with a 
community, how to use git, how to analyze data packets using Wireshark 
and tcpdump, how to create a project with Autotools, etc... :)
I'm undergoing a transformation from Windows developer to Linux 
developer. I'm like Jetfire from Transformer II, leaving the Decepticons 
for becoming an Autobot :p

> Yes, that's exactly it.  That's how the samba developers first implemented the
> SMB protocol of windows filesharing, and that's how we write OpenBSC and
> wireshark code for nanoBTS.
>   

So, you guys like challenges :)

> Also, the abis-oml.patch already includes support for parsing the test result
> messages of a nanoBTS.  See dissect_ipacc_test_rep() as well as
> ipacc_tr_ie_chan_usage and ipacc_tr_ie_bcch() in the attached patch.
>   

My Linux is just command-line for now, so I run Wireshark GUI in windows.

> No, we don't have other documentatio.  Just our common sense :)
>   

And a bit of sense of humor... :)







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