OpenBSC September 2025

openbsc@lists.osmocom.org

7 participants
6 discussions

More efficient RTP transport for CSD
by Mychaela Falconia 25 Sep '25

25 Sep '25

Dear Osmocom community, Those of you who had occasion to work with CSD probably noticed that the standard RTP payload format prescribed for AoIP by 3GPP Rel8+ (64 kbit/s CLEARMODE) is extremely wasteful: 160 bytes of payload every 20 ms (compared to a maximum of 33 bytes every 20 ms for voice calls), and most of that 160-byte CLEARMODE payload is constant filler. The actual information content for CSD channels traveling across A interface (data bits plus all metadata preserved, strictly lossless conversion) fits into 16 bytes for CSD modes up to 4.8 kbit/s, 32 bytes for 9.6 kbit/s or 37 bytes for 14.4 kbit/s - much more compact than the 160-byte standard! Because my non-profit org in USA (American 2G Cooperative) will soon be operating a public GSM/2G network as a membership co-op, we have a legal and ethical obligation to provide all services strictly at cost. Radio resource usage is exactly the same between voice and data calls, while CPU load on tw-border-mgw machines in the CN will often be even less with CSD than with EFR or AMR speech transcoding - hence there is no legitimate reason for CSD calls to be more expensive than voice. Yet the bloated RTP format prescribed by 3GPP Rel8+ artificially increases the cost of IP transport within the network. My solution to the problem: yet another TW-TS, specifying a modified version of AoIP interface with compressed CSD. Here is the spec: https://www.freecalypso.org/specs/tw-ts-007-v010001.txt An updated version of TW-TS-003 (BSSMAP extension spec) spells out how the MSC requests the use of compressed CSD instead of standard TS 48.103 on AoIP by adding RTPext IE to ASSIGNMENT REQUEST or HANDOVER REQUEST, with the right bit set to request TW-TS-007 RTP format. In terms of implementation of this newly defined feature in Osmocom, my plan is as follows: * Within the past couple of years I extended osmo_trau2rtp() and osmo_rtp2trau() to support CSD on E1 BTS, using standard CLEARMODE format on RTP side. I plan to extend these functions to support TW-TS-007 as well. * Combination of mainline OsmoBSC plus tw-e1abis-mgw has fully working CSD with E1 BTS, already tested with Nokia InSite. If my idea for representing TW-TS-007 compressed CSD format in MGCP/SDP is acceptable (please see chapter 9 and Annex A in the spec linked above), I would like to extend OsmoBSC to be able to command tw-e1abis-mgw via MGCP/SDP to emit either standard CLEARMODE or TW-TS-007 per request from MSC. The above points are for E1 BTS. With IP-native OsmoBTS, we have two options: 1) We could add more logic to OsmoBTS to emit either standard CLEARMODE or TW-TS-007, just like we already do for TW-TS-001/002 carrying TRAU-UL metadata bits for FR/HR/EFR. 2) We could leave OsmoBTS completely unchanged, speaking only standard CLEARMODE format for CSD, and have OsmoBSC-associated OsmoMGW convert on the fly (we are dealing with strictly lossless conversion here, not bringing back extra metadata as with other TW-TS) if the MSC asked for TW-TS-007 compressed RTP format. Option 2 seems easier to implement, and I am leaning toward this option. Of course this option only makes sense when osmo-bsc, osmo-mgw and osmo-bts-trx run on the same SBC next to or inside SDR-based BTS, or when the link between the BSC and the BTS is a local Ethernet cable, while A interface travels across public Internet or other networks where bandwidth matters. What does the community think? For my own operation E1 BTS is a higher priority (I still plan on using surplus Ericsson RBS6k gear), hence there is plenty of time for Osmocom community to provide feedback on how y'all would like to see this mechanism working with IP-native OsmoBTS. In terms of upcoming Gerrit patches related to TW-TS-007, I plan to work on libosmo-abis next, implementing lossless conversion functions and extending osmo_trau2rtp() and osmo_rtp2trau() for efficient, native support of compressed CSD. GSM/2G Forever, Mother Mychaela P.S. If anyone has constructive criticism regarding chapter 9 or Annex A in the TW-TS-007 spec linked above (AoIP and SDP aspects), it is not too late to revise those parts.

2 2

Financial Accounting Assignment Help
by Katherine Salvator 23 Sep '25

23 Sep '25

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1 0

Mobile disassociates from sysmobts 1002 after call
by Christoph Quirin Lauter 10 Sep '25

10 Sep '25

Hello, I am sorry, this might not be the right place to ask. I am kind of a newbie to the osmocom stack as well, so please be gentle with me. I recently got an FCC license in the 900MHz range and I am running sysmobts 1002 at home. I have updated it from NITB to the modern world of course. Everything seems to work as it should but there is one issue: A Pixel 9 Pro Android phone with a sysmocom SIM card (999/70) connected to the sysmobts disassociates -in certain cases- with the BTS/BSC after a call and displays "No network". It will never reassociate again, unless I put the phone in airplane mode and back on. Then it reassociates immediately again. I cannot see anything particular in the osmo-bsc/osmo-bts-sysmo logs but as I said, I am a newbie. I will be happy to post the logs if this is helpful. The issue does not arise for each call, only certain calls. I use osmo-sip-connector to an asterisk. Is this a known issue? Is it an issue with the phone? Did I configure something in a wrong way? I will do some experiments with another GSM phone. Thank you! Christoph Lauter

7 16

Move vlr code from osmo-msc into a own library
by Alexander 'lynxis' Couzens 10 Sep '25

10 Sep '25

Hi, a couple month ago I proposed to make the VLR code of the osmo-msc independent of the osmo-msc and create a new library called libosmo-vlr. Later use the libosmo-vlr code to integrate it into osmo-sgsn. But after take more time of this approach, I'm not sure if it is a very good idea to guarantee high stability of libosmo-vlr as we do for other osmocom libraries. Because the code is heavily integrated with both daemon and some code path are quite complex and partly not fully understood. I would rather guarantee runtime stability within a library version, but not at build time. The strategy would be increasing the library major version more often. Any thoughts? Best, lynxis PS. The current concept (because of time pressure) is to keep 2 copies of libosmo-vlr in the code base of osmo-msc and osmo-sgsn and to move it later out of it into an own library.

3 2

Having trouble balancing GSM projects and coursework?
by fennellmarian018＠gmail.com 08 Sep '25

08 Sep '25

As someone knee-deep in OpenBSC settings and attempting to gain a firm understanding of BTS to BSC handovers, I've struck a stumbling block in balancing my technical deep dives with academic duties. Between tracing Abis interface logs and diagnosing paging issues, I barely have time to concentrate on my finance studies. To be honest, I've pondered finding someone to take my accounting class for me so that I can continue with my telco experiments here. I'm not sure whether anyone else is dealing with the same workload, but if you've discovered a solid workflow or technique, I'd love to hear about it because OpenBSC is currently capturing my full attention. visit: https://takemycourseforme.us.com/pay-someone-to-take-my-online-accounting-c…

2 1

Struggling with Assignments? Let’s Talk About It!
by teves20525＠binafex.com 05 Sep '25

05 Sep '25

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OpenBSC September 2025