Cellular Network Infrastructure » cni-legacy » OpenBSC » OsmoNITB

please preferrably also include the version of the openbsc package (or whatever debian package includes the OsmoNITB binary exposing this behaviour). You can always use 'show version' on the vty.

OpenBSC version: 0.15.0.498-582e4

it would be great to not only have the pcap file, but also have detailed log output, particularly of the SMS logging subsystem.

By looking at the libpcap traces the osmo-nitb writes I was able to spot that the CP-ACK message is missing when a silent call runs. On the first look this gives the impression that the phone woule be unable to send the CP-ACK for some reason. However, the logtext shows something different:

Thu Jan 19 14:51:24 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:24 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9
Thu Jan 19 14:51:24 2017 <0022> silent_call.c:79 Discarding L3 message from a silent call.
Thu Jan 19 14:51:25 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:25 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9
Thu Jan 19 14:51:25 2017 <0022> silent_call.c:79 Discarding L3 message from a silent call.
Thu Jan 19 14:51:35 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:35 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9
Thu Jan 19 14:51:35 2017 <0022> silent_call.c:79 Discarding L3 message from a silent call.
Thu Jan 19 14:51:35 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:35 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9
Thu Jan 19 14:51:35 2017 <0022> silent_call.c:79 Discarding L3 message from a silent call.
Thu Jan 19 14:51:44 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:44 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9
Thu Jan 19 14:51:44 2017 <0022> silent_call.c:79 Discarding L3 message from a silent call.
Thu Jan 19 14:51:45 2017 <0000> abis_rsl.c:2009 (bts=0,trx=0,ts=0,ss=1) SAPI=3 DATA INDICATION
Thu Jan 19 14:51:45 2017 <0000> gsm_04_08.c:3723 Dispatching 04.08 message, pdisc=9

Looking for "Discarding L3 message from a silent call" in silent_call.c we find the following:

/* receive a layer 3 message from a silent call */
int silent_call_rx(struct gsm_subscriber_connection *conn, struct msgb *msg)
{
    /* FIXME: do something like sending it through a UDP port */
    LOGP(DLSMS, LOGL_NOTICE, "Discarding L3 message from a silent call.\n");
    return 0;
}

I still wonder why I do not see the CP-ACK message in the pcap file. Probably osmo-nitb only records messages that are actually processed. Looking at the original trace from Ivalo one can see that the CP-ACK messages are transmitted alog with CP-ERROR messages. My guess is that the CP-ERROR is the result of a slighty confused SMS-Protocol state.

The issue probably can be fixed by fixing the implementation of silent_call_rx() in a way that it forwards the incoming CP-ACK to the SMS protocol stack of osmo-nitb.

Removed the fuzzer code by placing ifdefs around it, since I am not sure if it is good to remove it entirely (maybe we should?). SMS now works as expected.

See also: https://gerrit.osmocom.org/#/c/1930/