OpenBSC

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17 participants
4217 discussions

Front and back sides of an MSC
by Mychaela Falconia 29 Nov '25

29 Nov '25

Hello Osmocom community, I have a question about terminology that is not really specific to Osmocom, but is specific to GSM/3G/etc cellular industry, or whatever is left of it. An MSC in a GSM or 3G or any other circuit-switched cellular network has two sides: one side facing the RAN (A interface in GSM, IuCS in 3G), the other side facing PSTN or ISDN or BICC or SIP-I or whatever the fixed telephone network may be. My question: is there a general industry-wide agreement as to which side should be called the front and which should be called the back? To me it seems intuitive to refer to the A/IuCS side of an MSC as the front and the PSTN/ISDN/BICC/SIP-I side of the same MSC as the back. However, I am just one person, and I have no idea whether or not my view is intuitive to others. And it would even worse if the opposite convention happens to be widely used... Hence I am asking this community, in the hope that someone with more industry experience would know how telco network engineers casually refer to RAN-facing and fixed-network-facing sides of an MSC. For a long time I had the idea of building ThemWi MSC as a modular system (multiple processes talking to each other via sockets) with a stripped-down OsmoMSC derivative as the "central" component, and with a radically different placement of MSC-MGW. However, as I started working on more detailed design, I realized a major flaw in my originally envisioned architecture: my original approach to MSC-MGW would break TFO for AMR, specifically the dialogue between TFO-aware BTS and the TRAU equivalent in the MGW. I am now spinning a new architecture in my head, one which tentatively includes two dissimilar MGWs in the MSC. If my front vs back terminology is valid, then the front MGW (talking to AoIP user plane) would perform speech transcoding but become a transparent pass-through for CSD (basically a software-only, IP-based equivalent of a hardware TCSM colocated at the MSC site), while the back MGW would be a transparent pass-through for speech calls, but turn into a complex IWF for CSD. This tentative architecture exactly matches the placement of speech transcoding and CSD IWF functions in traditional hardware MSCs of TDM-based, before-AoIP world. But I need to know if I should keep these front and back terms, or swap them the other way around. M~

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osmo-trx tx/rx Tx / Rx sample offset measure
by nero.moonnn＠gmail.com 28 Nov '25

28 Nov '25

Hello, everyone! How can I correctly measure the TX/RX sampling offset? I need to implement a new sampling frequency (7.68e6) for usrp b200. I added the coefficients for the receiver, and the transmission looks fine, but the reception is not working. I think it's all about the TX/RX sampling offset. What are some ways to measure this offset? Maybe there's something ready-made?

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osmo-trx-ms documentation
by Степан Королев 28 Nov '25

28 Nov '25

Hello. I'm looking for a replacement for grgsm_trx, and I came across osmo- trx-ms in the osmo-trx repository. But I came across a lack of information about this project. You can find out its status and whether it is recommended to use it in principle as a Front-End SDR for osmocom-bb mobile.

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cmd2 update causing pySim-shell to fail
by bryan coxwell 28 Nov '25

28 Nov '25

Hi all, Just wanted to share an issue and a quick workaround I found for it in case anyone else has the same problem. I believe a cmd2 update is causing pySim-shell to fail. After installing it on a fresh install of Ubuntu Server 20.04 and getting the following error when I run "python3 pySim-shell -p0": >Using PC/SC reader interface >Autodetected card type: sysmoUSIM-SJS1 >AIDs on card: > USIM: a0000000871002ffffffff8907090000 >Traceback (most recent call last): > File "pySim-shell.py", line 512, in <module> > app = PysimApp(card, rs, opts.script) > File "pySim-shell.py", line 59, in __init__ > super().__init__(persistent_history_file='~/.pysim_shell_history', allow_cli_args=False, use_ipython=True, auto_load_commands=False, command_sets=basic_commands, >startup_script=script) >TypeError: __init__() got an unexpected keyword argument 'use_ipython' If you run into this you can fix it by uninstalling cmd2 and reinstalling cmd2 with "pip3 install cmd2==1.5". Best, Bryan

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27 Nov '25

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New MGW for E1 Abis, future ThemWi sw plans
by Mychaela Falconia 24 Nov '25

24 Nov '25

Dear Osmocom community, I am pleased to announce the first usable version of my new MGW for use with OsmoBSC and E1-based BTS: https://gitea.osmocom.org/themwi/tw-e1abis-mgw This new sw component works as a drop-in replacement for osmo-mgw in the role of BSC-associated MGW for E1 Abis. Principal new features compared to OsmoMGW-E1 are: * The path from RTP input to fixed-timing TRAU-DL output passes through ThemWi jitter buffer (twjit), instead of blindly converting every received RTP packet to a TRAU-DL frame, queueing those frames to I.460 MUX Tx and hoping for the best. * For FR codec in the present implementation and for EFR coming later, a proper UL-to-DL transform (aka TFO transform) is applied to this RTP-to-DL path. This way if the stream of UL frames from the other call leg includes gaps due to radio errors, FACCH stealing or DTXu pauses, or if gaps are caused by packet loss, the stateful transform will produce proper error concealment or comfort noise insertion per TS 28.062 section C.3.2.1.1. * CSD is supported! This development may be the first time in Osmocom history of CSD working on an E1-based BTS. I tested this new MGW with Nokia InSite BTS and confirmed it working with all 3 classic GSM voice codecs (FR, HR and EFR) and with CSD up to 9600 bps. CSD at 14400 bps (D145_SYNC and EDATA frames) is supported too, but remains untested due to lack of needed support in OsmoMSC. My eventual goal is to use OsmoBSC and this new MGW with Ericsson RBS6k BTS, consisting of DUG20 and RUS or RRUS. I already have DUG20 and RUS01 hardware, but given all other work I still have to do on ThemWi CN software, I haven't got around to playing with Ericsson gear yet. My plans going forward are: * Get back to twrtp patches in Gerrit: implement the next round of changes per last round of review, and hopefully get twrtp into libosmo-netif so we can make it an option in OsmoBTS, in addition to E1 BTS. * Finish long-deferred work on libgsmhr1 in gsm-codec-lib. HRv1 codec is of course of no practical interest, can be regarded as a "just for fun" retronetworking feature, but I need to finish it so certain ThemWi components can rely on having encoders and decoders for all GSM codecs always available, and my TFO transform for HRv1 will serve as a stepping stone toward much more important TFO transform for EFR. * After the above, the big work item for me will be ThemWi-MSC. I won't get into details as I don't like writing about vaporware, but many of you know that currently I am still stuck on 2023-02 version of OsmoMSC while running newer versions of all other components. ThemWi-MSC will be my proper solution, but I'll write about it in detail only when it becomes a reality. Never stopping work toward restoration of top-quality GSM/2G networks, Mother Mychaela

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Digital Frontiers: Online Platforms and Media Expansion in Uzbekistan
by vanjohnson716＠proton.me 23 Nov '25

23 Nov '25

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Splitting out M3UA and MTP3 out of Open BSC into a separate library
by Arran Cudbard-Bell 20 Nov '25

20 Nov '25

Hi, Developing a module for FreeRADIUS to support EAP-SIM and EAP-AKA authentication against a HLR. The HLR we were targeting only supported a SCTP/M3UA/SCCP/TCAP/MAP stack, so we couldn't use SUA. Ripping the M3UA/MTP3 code out of OpenBSC worked surprisingly well. We ended up running the event loop in a separate thread to work around the threading issues. Unfortunately the HLR implements the ANSI variant of everything, whereas OpenBSC and supporting libraries seem to have been written to be compatible with the ITU standards. ...but the differences are fairly minor at MTP3 and SCCP layers, and i've started work on a patchset for libosmo-sccp. https://gerrit.osmocom.org/#/c/73/ Anyway, trying to gauge interest in splitting those layers out of Open BSC into a separate library, would be happy to take on M2UA as well for consistency. It would almost certainly get more projects using the code. There's very little out there even in Perl land for working with SS7. Thanks, -Arran Arran Cudbard-Bell <a.cudbardb(a)freeradius.org> FreeRADIUS Development Team FD31 3077 42EC 7FCD 32FE 5EE2 56CF 27F9 30A8 CAA2

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Managing Complicated Laws in BSC Implementations
by Fennellmarian018＠gmail.com 20 Nov '25

20 Nov '25

The complexities of Base Station Controller (BSC) integration in open-source mobile networks have presented me with a number of overlapping areas pertaining to telecommunications legislation and regulatory compliance. In order to better comprehend how international legal standards affect open BSC installations in various jurisdictions, this intersection has unanticipatedly prompted me to seek [url=https://dissertationwritinghelp.uk/law-dissertation-help/]law dissertation help[/url]. I would love to hear from anyone else who has studied legal issues in their OpenBSC-related academic or practical work, as well as suggest some books.

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19 Nov '25

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