Analysing the communication between the BSC and the MSC in a sysmoBTS

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Yann R. Moupinda yannm1 at hotmail.com
Tue Oct 2 14:56:00 UTC 2012





Hello everybody



First of all, let me introduce myself. My name is Yann Moupinda and I'm 
a student doing his Master thesis in the field of

GSM technology. For my thesis, the company for which i'm working now, 
bought a sysmoBTS from sysmocom. The

sysmoBTS is configured as a stand alone  GSM network in a box (NITB) 
running the osmo-nitb and the osmo-bts programs.



An important part of my thesis is to understand how the sysmoBTS works 
and therefore I did some measurements with

wireshark to analyse the data flow between the BTS,BSC and 
MSC/HLR/VLR/EIR. This is also to see the main differences between a 
sysmoBTS and a conventional GSM Network.



I used the " tcpdump " - command on the loopback interface lo0 to 
capture the data flow between the GSM components and then, the analysis 
with wireshark shows me only the data flow between BTS and BSC. It's 
possible to see such messages like LOCATION UPDATING REQUEST and 
IDENTITY REQUEST wich are normally, transparently exchanged between 
Mobile Station (MS) and the Network subsystem (MSC/HLR/VLR/EIR). All 
these messages are always addressed to, or from  the same BSC TCP-port 
3003. So i can not see what happens behind this port (behind BSC).

In order to get the communication between  BSC and MSC, i decided to 
have a deeper look on the logging messages of the sysmoBTS. Even there, 
i cannot recognize how the data transmission between BSC and MSC works.



Does anyone know how to get this information? Any guidance would be 
appreciated.



I have included one .pcap file and a text file of the logging messages 
taken while i powered on the mobile phone.



Best regards,

Yann.


 		 	   		   		 	   		  
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