CalypsoBTS timeslots allocation

Вадим Яницкий axilirator at gmail.com
Mon Sep 14 20:39:46 UTC 2015


Thanks for the explanations, Sylvain. I understood that. I hope Andreas too
reads the Mailing lists because he does not respond to my letter.

With one phone everything (USSD, SMS, Location Updates) works fine and
stable, except the voice calls and some network visibility problems. I
think with OsmoBTS it works even more stable than with OpenBTS. With two
phones the network is less stable and it's range of coverage is smaller
than with one phone. Sometimes (not always) the voice calls forwards to the
LCR (995 and 993 numbers) but I do not hear anything...

As I understand:
1. When just one phone as TRX (TT_R_TTT), OpenBSC uses only TS0 to transmit
CCCH and SDCCH4 data. Other (TS 1,5,6,7) TX time slots are used to transmit
DUMMY BURSTS in order to increase the ARFCN power.
2. When two phones are connected as TRX[0] (T__R_TTT) and TRX[1]
(_T__R___), TS1 does not carries DUMMY BURSTS, it is used for TCH channel.
TS4 at the Downlink (that is not used by TRX[0]) now is used to receive TCH
data from phones connected to the network. Total TS allocation layout is
TT_RRTTT. TS2 is not used. TS 5,6,7 are for DUMMY BURSTS. Ok, it works.
3. But what if I enable TS2 to transmit one more TCH channel? In this case
I should exclude TS5 from the tx_mask because it is TS2 at the Uplink. I
changed the old TX/RX masks for TRX[0] and TRX[1] to these:
as->l1l[0].tx_mask = 0xc1; // 10000011 - TS 0,5,7 //
as->l1l[0].rx_mask = 0x01; // 10000000 - TS0 at the UL or TS3 at the DL //
as->l1l[1].tx_mask = 0x06; // 01100000 - TS 1,2 //
as->l1l[1].rx_mask = 0x06; // 01100000 - TS 1,2 at the UL or TS 4,5 at the
DL //

TRX[0]'s layout is T__R__TT.
TRX[1]'s layout is _TT_RR__.
Total layout is TTTRRRTT.

It looks like cool at the paper but does not work...
In the osmocon console of TRX[0] everything looks good.
In the osmocon console of TRX[0] I see many repeating "DSP Error 24"
messages. And the network does not work. :((

The questions that very interested to me:
1) Why my TTTRRRTT layout does not work? What does it mean (DSP Error 24)?
2) When does it send SCH BURSTS?
3) Is it possible to transmit with one phone and receive with another?
4) When I am using the jolly/testing branch with OpenBSC, I often see this
messages in osmocon console:
TOA=4 snr=16384 (thres 2560) freq_err=77 pm=-89
TOA=4 snr=16384 (thres 2560) freq_err=24 pm=-89
And this in NITB console:
<0004> abis_rsl.c:1471 (bts=0,trx=0,ts=0,ss=0) Activating ARFCN(<ARFCN>)
SS(0) lctype SDCCH r=LOCATION_UPDATE ra=0x00 ta=46
<0004> abis_rsl.c:1195 (bts=0,trx=0,ts=0,ss=0) CHANNEL ACTIVATE ACK
<0004> abis_rsl.c:680 (bts=0,trx=0,ts=0,ss=0) RF Channel Release CMD due
error 1
<0004> abis_rsl.c:634 (bts=0,trx=0,ts=0,ss=0) DEACTivate SACCH CMD
<0004> abis_rsl.c:732 (bts=0,trx=0,ts=0,ss=0) RF CHANNEL RELEASE ACK
<0004> abis_rsl.c:649 (bts=0,trx=0,ts=0,ss=0) is back in operation.
<0004> abis_rsl.c:1471 (bts=0,trx=0,ts=0,ss=0) Activating ARFCN(<ARFCN>)
SS(0) lctype SDCCH r=LOCATION_UPDATE ra=0x00 ta=19
<0004> abis_rsl.c:1195 (bts=0,trx=0,ts=0,ss=0) CHANNEL ACTIVATE ACK
<0004> abis_rsl.c:1471 (bts=0,trx=0,ts=0,ss=1) Activating ARFCN(<ARFCN>)
SS(1) lctype SDCCH r=LOCATION_UPDATE ra=0x00 ta=59

Is it normal? I did not seen this messages when run OpenBSC with
sylvain/testing branch.
5) Is it possible to run one more transceiver process as a new trx section
in the parent "bts 0" section of the open-bsc.cfg file?

Have a nice day,
Яницкий Вадим.

2015-09-07 12:38 GMT+06:00 Вадим Яницкий <axilirator at gmail.com>:

> Hello, list! I am trying to make working two and more TCH channels in
> OpenBSC (NiTB mode) with calypso based phones. How to understand timeslots
> allocation in this strings of transceiver app?
> as->l1l[0].tx_mask = 0xe3; /* TS 5,6,7,0,1 */
> as->l1l[0].rx_mask = 0x01; /* TS 0 */
> Why 2, 3, 4 timeslots is not used?
> And how to connect more than two phones to the transceiver? Should I add a
> new TRX in OpenBSC config and/or modify source code of the transceiver app?
>
> With best regards, fixeria.
>
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