CBCH support for osmo-bts-trx

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Tomcsányi, Domonkos domi at tomcsanyi.net
Wed Sep 19 16:54:16 UTC 2018


Hi Lorenzo,

Try, if possible, to put a Qualcomm chipset based phone with some kind of tracing (e.g. Snoopsnitch) under testing. It might yield some results looking into the PCAP file.
Wireshark dissectors can help sometimes catching wrongly coded messages - at least they helped me in the past.

Good luck!

Cheers,
Domi


2018. szept. 19. dátummal, 13:40 időpontban Lorenzo Cavallini <lorenzo.cavallini at gmail.com> írta:

> Hi,
> 
>> On Tue, Sep 18, 2018 at 10:10 PM Harald Welte <laforge at gnumonks.org> wrote:
>> Hi Lorenzo,
>> 
>> FYI, even the (to me hyper-modern) Samsung Galaxy S5 decodes the messages here.
>> I mostly work with >= 10 year old feature phones during development, as their UI
>> is inside the baseband processor and closer to what happens on the GSM protocol side
>> than all the smartphones that go via AT-commands or QMI.
> I think the main issue is that Samsung switched baseband after the S5. I tested just now on the S7 and it's not working.
>  
>> > Anyway, the location update procedure is
>> > successfully completed in all three phones I've tested.
>> 
>> that's great and confirms the related bug is fixed.
> You can add iPhone7 and Galaxy S7 to the list of phones that can successfully complete the location update procedure, with the SDCCH4+CBCH configuration. On the other hand, on a very old Huawei LUA-L21 I'm not even able to receive the BCCH, my cell is not present in the list. I'm not 100% sure that's related to osmocom stack here, this phone is in a really bad shape overall, but it works without CBCH.
>  
>> I'm not sure why that is.  One thing to try is to use CBCH on SDCCH/8, and also
>> to ensure that those very same phones with their firmware/software and configuration
>> will show SMSCB on other/production GSM networks (in 2G-only mode!!).
> I'm pretty much sure that my iPhone8, Honor 9 and Galaxy S7 can receive broadcast notifications, because I get them during network tests for floods and other calamities in my country. However, I never checked if they're delivered through Paging Type 1 rest octets or through SMSCB, so this might make a difference. And to be honest I don't remember if I was in 2G only mode or not, but they test them once per month, so in about 2 weeks I can check this :)
> 
>> The OsmoBTS implementation of CBCH is very conservative.
>> * it doesn't use the optional DRX cycle
>> * it doesn't use the optional extended CBCH
>> * it definitely sends the blocks at the right time in the multiplex as per TS 05.02,
>>   I verified this several times
> I'm going to retest all my mobile phones with the SDCCH8+CBCH configuration and see if this makes a difference. I will let you know.
> Unfortunately I don't have any pre-iPhone era phones that still work beside my Samsung, so I cannot test anything else for a "positive" result.
> Thanks!
> 
> Regards,
> 
> Lorenzo
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