Hello everybody,
after starting on my new Job at an University I have been tasked to build up an BTS for our students.
Being a complete noob to both Linux and GSM it took me some time, but I finally got OpenBSC and Osmo-BTS up and running on Ubuntu Linux 12.04 with our ETTUS N210. After doing some experiments with this setup, our students now ask me to do some changes which I couldn't figure out yet, how to do.
1. The students told me, that OpenBSC doesn't behave like all the BTS from commercial Providers they analysed: The say that on commercial nets at the beginning of a phone call there will be send an "Immediate assignment" sending the MS always to a SDCCH on TS 1 or TS2 where the encryption will be startet. After establishing the encryption another "Immediate assignment" will occour and send the MS to a Traffic Channel (which also contains the FACCH / SACCH) for the actual Communication. OpenBSC also sends the "Immediate assignment" on TS0 but sends the MS directly to Timeslot with a Traffic Channel where all the signalling, like encryption, will be done in the SACCH. Is there any way to configure OsmoBSC to behave like the commercial BTS the students described?
2. I have been asked if I could enable "Frequency Hopping" Right now I already fail to bring up a second TRX with OpenBSC. I start 2 instances of "osmo-trx" with 2 differents IP-Addresses but the same port, after that I start "osmobts-trx" with the "-t 2" parameter. OpenBSC seems to see both USRPs but the LED'S an the USRPs indicate that only one is completely powered up and transmitting (a quick check with an Motorola with RSSI also shows only one ARFC). So how do I have to start "osmo-trx" to enable transmitting on both URSPs as TRX0 and TRX1 in one BTS? After that, is it possible to configure "Frequency hopping" with this setup? (Because when I changed the value "hopping enabled" of the timeslots in open-bts.cfg to "1" I get a message that this type of BTS does not support hopping)
I hope that anyone can clarify those two points to me.
Thanks in advance
Norbie
On Mon, Jul 07, 2014 at 01:39:06PM +0200, Norbert Englberger wrote:
Hello everybody,
Hi,
- The students told me, that OpenBSC doesn't behave like all the BTS from
commercial Providers they analysed: The say that on commercial nets at the beginning of a phone call there will be send an "Immediate assignment" sending the MS always to a SDCCH on TS 1 or TS2 where the encryption will be startet. After establishing the encryption another "Immediate assignment" will occour and send the MS to a Traffic Channel (which also contains the FACCH / SACCH) for the actual Communication. OpenBSC also sends the "Immediate assignment" on TS0 but sends the MS directly to Timeslot with a Traffic Channel where all the signalling, like encryption, will be done in the SACCH. Is there any way to configure OsmoBSC to behave like the commercial BTS the students described?
it is not a question of BTS but the BSC. The role of the BSC is to manage the channels. Inside src/libbsc/gsm_04_08_utils.c you will see a table that determines how the BSC/NITB will respond to "channel request" inside the RACH request by the phone.
E.g. if you change get_ctype_by_chreq to always return LCHAN_SDCCH you should be close to the behavior you have described.
Hi Norbert,
07 июля 2014 г. 15:40 пользователь "Norbert Englberger" < Norbert.Englberger@unibw.de> написал:
- I have been asked if I could enable "Frequency Hopping"
Right now I already fail to bring up a second TRX with OpenBSC. I start 2 instances of "osmo-trx" with 2 differents IP-Addresses but the same port, after that I start "osmobts-trx" with the "-t 2" parameter. OpenBSC seems to see both USRPs but the LED'S an the USRPs indicate that only one is completely powered up and transmitting (a quick check with an Motorola with RSSI also shows only one ARFC). So how do I have to start "osmo-trx" to enable transmitting on both URSPs as TRX0 and TRX1 in one BTS? After that, is it possible to configure "Frequency hopping" with this
setup?
(Because when I changed the value "hopping enabled" of the timeslots in open-bts.cfg to "1" I get a message that this type of BTS does not support hopping)
Using two osmo-trx's or two devices with a single osmo-trx is not supported at this moment and there are no current plans to support this configuration, AFAIK.
That said, we're working on supporting frequency hopping with a single device. I expect this to be ready for testing in the next few months.
Please excuse typos. Written with a touchscreen keyboard.
-- Regards, Alexander Chemeris CEO Fairwaves, Inc. https://fairwaves.co
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Alexander Chemeris -
Holger Hans Peter Freyther -
Norbert Englberger