Working with OpenBSC + Osmocon: Paging response fails to activate SDCCH

David Bahr dave.meathead at googlemail.com
Tue Mar 20 18:33:49 UTC 2012


Hi,

Ive just setup  an OpenBSC + nanoBTS environment to experiment around with
your Osmocom software and a Motorola C123. I tried wo write a little
application similiar to app_ccch scan, which is able of responding to
paging requests by sending a rach request and the following paging response
procedure. The rach access is working fine, but i cant get the paging
response to work properly. The message itself is correct (layer2/layer3
parts) according to the specs. OpenBSC is also working correctly as it is
working with my normal cell phone or your mobile application.
What i'm doing in my code is the following:
1. After getting the immediate assignment i call l1ctl_tx_dm_est_req_h0 in
l1ctl.c (l1ctl_tx_dm_est_req_h0(ms,    arfcn, ia->chan_desc.chan_nr,
ia->chan_desc.h0.tsc, GSM48_CMODE_SIGN, 0)) in order to tune to the
assigned channel (or the h1 procedure for hopping).
2. Afterwards i build the paging response (layer2 + layer3), pad the msg
and send it via osmo_send_l1(ms, msg) similiar to l1ctl_tx_data_req in
l1ctl.c

That it is not working can be seen in the OpenBSC abis debug output:
<0004> abis_rsl.c:1318 (bts=0,trx=0,ts=0,ss=0) Activating ARFCN(514) SS(0)
lctype SDCCH r=OTHER ra=0x67 ta=0
<0004> abis_rsl.c:1064 (bts=0,trx=0,ts=0,ss=0) CHANNEL ACTIVATE ACK
<0004> abis_rsl.c:891 (bts=0,trx=0,ts=0,ss=0) CONNECTION FAIL: RELEASING
CAUSE=0x01(Radio Link Failure)
<0004> abis_rsl.c:621 (bts=0,trx=0,ts=0,ss=0) RF Channel Release CMD due
error 1
<0004> abis_rsl.c:658 (bts=0,trx=0,ts=0,ss=0) RF CHANNEL RELEASE ACK
<0004> abis_rsl.c:594 (bts=0,trx=0,ts=0,ss=0) is back in operation.

It should be looking like this:
<0004> abis_rsl.c:1318 (bts=0,trx=0,ts=0,ss=0) Activating ARFCN(514) SS(0)
lctype SDCCH r=OTHER ra=0x10 ta=0
<0004> abis_rsl.c:1064 (bts=0,trx=0,ts=0,ss=0) CHANNEL ACTIVATE ACK
<0000> abis_rsl.c:1490 (bts=0,trx=0,ts=0,ss=0) SAPI=0 ESTABLISH INDICATION
<0003> gsm_04_08.c:1076 PAGING RESPONSE: mi_type=0x04 MI(...)

Has anyone an idea what I'm doing wrong? Thanks in advance for any help!

Best regards,
David
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