OpenBSC December 2025

openbsc@lists.osmocom.org

26 participants
38 discussions

Front and back sides of an MSC
by Mychaela Falconia 17 Feb '26

17 Feb '26

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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cmd2 update causing pySim-shell to fail
by bryan coxwell 14 Feb '26

14 Feb '26

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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How to Effectively Prepare for the Oracle 1Z0-1127-25 Exam in Minimal Time
by mahmad.iworks＠gmail.com 12 Feb '26

12 Feb '26

Facing a certification exam can feel daunting, especially when time is short. The Oracle 1Z0-1127-25 exam tests a wide range of skills and concepts, requiring both conceptual understanding and practical application. However, with a structured approach, you can study efficiently and make the most of your available time. A good first step is to familiarize yourself with the official exam objectives. Oracle provides a detailed outline of the topics and skills assessed in the 1Z0-1127-25 exam. Breaking the syllabus into smaller, manageable sections allows you to prioritize areas that need the most attention. Start with high-weightage topics and ensure you have a strong understanding of core concepts before moving on to the more advanced material. Next, combine different study resources for a balanced approach. Textbooks, official documentation, and online tutorials are essential for conceptual clarity, but incorporating practice materials is equally important. Many candidates find Oracle <a href="https://www.pass4future.com/oracle/exam/1z0-1127-25">1Z0-1127-25 Exam dumps</a> helpful for familiarizing themselves with question patterns and time management. While these dumps should never replace proper study, they can highlight commonly tested areas and help simulate real exam conditions. Active learning techniques can also save time and improve retention. Creating quick notes, flashcards, or mind maps for complex topics allows for rapid revision. Additionally, scheduling short, focused study sessions, rather than long, unfocused hours, can boost concentration and prevent burnout. Finally, practice consistently. Even in minimal time, attempting mock tests regularly helps track progress, identify weak spots, and build confidence. Review mistakes carefully to ensure you don’t repeat them in the actual exam. By combining clear planning, strategic use of resources like Oracle 1Z0-1127-25 Exam dumps, and consistent practice, it is possible to prepare effectively even with limited time. Remember, the quality of study often outweighs quantity.

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Managing Complicated Laws in BSC Implementations
by Fennellmarian018＠gmail.com 11 Feb '26

11 Feb '26

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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Video Recordings of OsmoCon 2017
by Harald Welte 09 Feb '26

09 Feb '26

Hi all, the Osmocom Conference 2017 last week was an overwhelming success. We received lots of positive feedback from all sides. Thanks to all the speakers, to the attendees as well as to the anonymous sponsor of the travel grant funds. It is my great pleasure that due to the great support by C3VOC (The CCC Video Operation Center), we have full recordings of all talks given at OsmoCon 2017. You can find the videos on the C3VOC site at https://media.ccc.de/search/?q=osmocon They are also linked individually from the OsmoCon 2017 homepage at https://osmocom.org/projects/osmo-dev-con/wiki/OsmoCon2017 I hope the video recordings will be of help for everyone who could not make it to the event in person. We will also be collecting the slides and put them up on the wiki during the next few days. Please don't hesitate to raise any feedback and/or questions. Technical feedback/questions regarding Osmocom software / projects should be addressed to the appropriate mailing lists, such as openbsc(a)lists.osmocom.org. Feedback to the organizers should be sent to osmocon2017(a)sysmocom.de. Looking forward to the next OsmoCon, which we'll expect to be spanning ore than just a single day. Regards, Harald -- - Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)

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Brazilian Knots Salon
by Amelia Emery 05 Feb '26

05 Feb '26

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GPRS - local and foreign TLLIs
by Luca Melette 04 Feb '26

04 Feb '26

Hello everybody, after setting up a nanoBTS with OpenBSC/SGSN/GGSN, I had some troubles trying to connect my smartphone to the GPRS cell. Investigating the BTS-to-SGSN traffic, I saw that the frames sent by the SGSN were all marked with the same N(U) value (at LLC layer), the value was 0. With some debug, I found that the there was a mismatch in the TLLI storage, used to keep the status of attached terminals. The mentioned code is contained in gprs_llc.c, involving LL Entity functions and gprs_llc_tx_ui(). /* look-up or create the LL Entity for this (TLLI, SAPI) tuple */ lle = lle_by_tlli_sapi(msgb_tlli(msg), sapi); if (!lle) { struct gprs_llc_llme *llme; LOGP(DLLC, LOGL_ERROR, "LLC TX: unknown TLLI 0x%08x, " "creating LLME on the fly\n", msgb_tlli(msg)); llme = llme_alloc(msgb_tlli(msg)); lle = &llme->lle[sapi]; } The TX function uses the previously received TLLI to lookup for the LLE. The lle_by_tlli_sapi() performs the search, but preliminary it applies a foreign2local TLLI conversion to ensure to have a local one. Since no valid entry for the searched TLLI is found, a new one is created. And the problem is here. The new entry has the foreign TLLI. Next time the lookup fails again, and a new entry is created. This way, the counter N(U) is always reset, and the mobile do not recognize the message sequence and no attach is possible. My question is about foreign and local TLLIs. I patched the lookup, avoiding the conversion, so that the LLE is found and everything works fine... but... What is the sense of the conversion? Should the TLLI be always stored as a local one? Can this problem be solved with another foreign2local while allocating new entries? Actually, my problem has been solved with that workaround. But I'm curious to know what is the right way. Hope somebody can answer :) Thanks. Cheers, LM

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Re: AMR on E1 BTS with tw-e1abis-mgw
by Sipos Csaba 28 Jan '26

28 Jan '26

Hi Mychaela, The AMR capability works great with your drop-in MGW implementation, voice quality improved a lot. I also tested the FR/EFR part earlier, which also works as expected. CSD is definitely interesting, once I have at least two CSD capable devices, I will give that a try as well. We already tried with a Nokia MetroSite, and early next year I am planning to try with our UltraSite setup at the museum as well. Would be nice to be able to send fax on top of GSM :-) The OML dialect we have in Osmocom now (called "nokia_site") despite its name it supports old Nokia equipment up to Felxi EDGE, Multiradio and Multiradio10 (on E1), if anyone else is interested, so OML support is not limited to just the Nokia *Site family. Some of this stuff is still running in less fortunate countries... Little bit of tweaking will likely needed, but at least it is not a completely unknown part like AoIP. Regards, Csaba

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OsmoNITB timeslots configuration and UmTRX
by Родион Гадыршин 27 Jan '26

27 Jan '26

Hello, list. I have umtrx v2.1 and I have already built GSM and GPRS components. Now I want to know which way of configuring timeslots in osmobsc.cfn is the best. I want GPRS, calls and SMS work. My current configuration is: timeslot 0 phys_chan_config CCCH+SDCCH4 hopping enabled 0 timeslot 1 phys_chan_config SDCCH8 hopping enabled 0 timeslot 2 phys_chan_config TCH/F hopping enabled 0 timeslot 3 phys_chan_config TCH/F hopping enabled 0 timeslot 4 phys_chan_config PDCH hopping enabled 0 timeslot 5 phys_chan_config PDCH hopping enabled 0 timeslot 6 phys_chan_config PDCH hopping enabled 0 timeslot 7 phys_chan_config PDCH hopping enabled 0 Is there a better way to configure? Maybe better use TCH/F_TCH/H_PDCH, but I have heard, that TCH/F is currently not working in dynamic configurations - only TCH/H does. And there is no only TCH/H_PDCH mode. So, could you please give me an advice?

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On the use of 'decmatch' in TTCN-3
by Harald Welte 27 Jan '26

27 Jan '26

Hi, I know that TTCN-3 is still new to a lot of you, but we are writing tons of integration testing against the various osmocom programs in it. It is quite amazing technology, and I would like to ask you to bear with me reading this mail :) Pau was stating the question earlier today on not finding an example on how to use decmatch. Indeed, it took me some months to find that gem in the TTCN-3 world. It solves the problem that you often have during test of layered protocol stacks: you have separate encoders/decoders for each protocol layer, and now you want to match on some of the *inner* payload. So normally, you have some kind of header definition + a binary (octetstring) payload. This happens in RSL with the L3_INFO IE, and just the same on BSSAP/DTAP where again the L3 message (for example call control) is encapsulated inside one information element. Now you have multiple options of addressing the problem: a) hand-written calls to the decoder function b) write na 'emulation' for the entire protocol layer c) use decmatch. a) would look like this (pseudo-code): var octetstring l3oct; var RSL_Message rsl RSL.receive(tr_RSL_DATA_REQ(g_chan_nr, ?, ?)) -> value rsl { var PDU_ML3_MS_NW l3 := dec_PDU_ML3_MS_NW(rsl.payload); if (match(l3, some_template)) { ... do something } ... } Which uses the built-in pattern-matching on the RSL port to match any message that matches the tr_RSL_DATA_REQ template, and stores the resulting RSL message in a variable. It then uses an explicit call to the decoder function of the L3 message, and then uses regular conditional expressions for further matching on that inner L3 payload. This is more or less how you would write in C, python or any other quite imperative programming languages. It's very verbose, time consuming and un-abstract/elegant. TTCN-3 has many declarative aspects to it. Code like the above is a waste of your time :) b) would mean that you implement some test component that handles the RSL messages on its bottom side test port, and the L3 messages on its top side test port. That is a possible way, and if you need a lot of state/logic of RSL, it maeks sense. But what if you really simply want to have a match? Then it would be a lot of effort and a large detour. c) decmatch to the rescue! You can write RSL.receive(tr_RSL_DATA_REQ(g_chan_nr, ?, decmatch tr_RRM_RR_STATUS)) which means: * do a receive on the RSL test port, and match on an incoming RSL message that matches the tr_RSL_DATA_REQ template, with channel number specified, link_id any (?), *and* if the octetstring payload, if decoded, matches the template tr_RRM_RR_STATUS ! This is *extremely* powerful and expressive. It allows you to condense complex, parametric template matching over multiple proocol layers. It would in the end match RSL DATA REQUEST, only if they contained a [valid] encoded RR STATUS. See https://gerrit.osmocom.org/6229 for the actual test case I used for the above examples. Please also note that I never had to even write the function name of the decoder (dec_PDU_ML3_MS_NW), but TTCN-3 *automatically* figures out which decoder function it must call in order to decode from the binary octetstring. Happy (TTCN-3) hacking + Osmocom bugfixing, Harald -- - Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)

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