Cellular Network Infrastructure » Core Network (CN) » OsmoMSC

Looking at the CC code in osmo-msc, I notice this:

http://git.osmocom.org/osmo-msc/tree/src/libmsc/gsm_04_08_cc.c?id=a09f4987c1e636052a4e37dae9d183d5aea49a8f#n1944

                /* If subscriber has no conn */
                if (!msc_a) {

                        if (vsub->cs.is_paging) {
                                LOG_TRANS(trans, LOGL_DEBUG,
                                          "rx %s, subscriber not yet connected, paging already started\n",
                                          get_mncc_name(msg->msg_type));
                                vlr_subscr_put(vsub, __func__);
                                trans_free(trans);                   <--------- Problem?
                                return 0;
                        }

                        /* store setup information until paging succeeds */
                        memcpy(&trans->cc.msg, data, sizeof(struct gsm_mncc));

                        /* Request a channel */
                        trans->paging_request = paging_request_start(vsub, PAGING_CAUSE_CALL_CONVERSATIONAL,
                                                                     cc_paging_cb, trans, "MNCC: establish call");

If the subscriber has no conn yet, we Page it.
But if we are already Paging, we should keep the transaction and act on it once the Paging Response is received.
However, this code seems to free the transaction.

We need a test for this scenario:

• Subscriber is being Paged (e.g. for SMS or whatever), no Paging Response has come in yet
• An MT call is starting for this subscriber
• Expect the MT call to proceed

When the test has confirmed erratic behavior, see if this patch fixes the problem:

--- a/src/libmsc/gsm_04_08_cc.c
+++ b/src/libmsc/gsm_04_08_cc.c
@@ -1944,18 +1944,17 @@ static int mncc_tx_to_gsm_cc(struct gsm_network *net, const union mncc_msg *msg)
                /* If subscriber has no conn */
                if (!msc_a) {

+                       /* store setup information until paging succeeds */
+                       memcpy(&trans->cc.msg, data, sizeof(struct gsm_mncc));
+
                        if (vsub->cs.is_paging) {
                                LOG_TRANS(trans, LOGL_DEBUG,
                                          "rx %s, subscriber not yet connected, paging already started\n",
                                          get_mncc_name(msg->msg_type));
                                vlr_subscr_put(vsub, __func__);
-                               trans_free(trans);
                                return 0;
                        }

-                       /* store setup information until paging succeeds */
-                       memcpy(&trans->cc.msg, data, sizeof(struct gsm_mncc));
-
                        /* Request a channel */
                        trans->paging_request = paging_request_start(vsub, PAGING_CAUSE_CALL_CONVERSATIONAL,
                                                                     cc_paging_cb, trans, "MNCC: establish call");