[MME] unify EPS Bearer Context Status (BCS) check for both active_flag=0 and 1

Previously, TAU procedure validated EPS Bearer Context Status (BCS)
only when active_flag == 0. When active_flag == 1, the MME skipped BCS
validation and sent TAU ACCEPT directly via InitialContextSetup.

This patch unifies BCS validation so both active_flag paths handle
bearer mismatches consistently. It also selects the correct S1AP
procedure (InitialContextSetup or DownlinkNASTransport) depending on
the UE active state.

Changes:
- emm-sm.c / sgsap-handler.c:
  * Always check EPS_BEARER_CONTEXT_STATUS_TYPE presence.
  * Invoke mme_send_delete_session_or_tau_accept() for both
    active_flag=0 and 1.
  * Send TAU ACCEPT directly only when BCS is not present.

- mme-path.c:
  * Select S1AP procedure in TAU ACCEPT based on active_flag.

- mme-s11-handler.c:
  * After Delete Session Response (OGS_GTP_DELETE_SEND_TAU_ACCEPT),
    send TAU ACCEPT using proper S1AP procedure by active_flag.

This aligns MME TAU behavior with 3GPP TS 24.301 section 5.3.3.0a,
ensuring consistent BCS synchronization regardless of UE activity.

src/mme/emm-sm.c

@@ -729,24 +729,27 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e,
                         ogs_kdf_nh_enb(mme_ue->kasme, mme_ue->kenb, mme_ue->nh);
                         mme_ue->nhcc = 1;
 
-                        ogs_info("[%s] TAU accept(active_flag=1)",
+                        ogs_info("[%s] KDF update(active_flag=1)",
-                                mme_ue->imsi_bcd);
-                        r = nas_eps_send_tau_accept(mme_ue,
-                                S1AP_ProcedureCode_id_InitialContextSetup);
-                        ogs_expect(r == OGS_OK);
-                        ogs_assert(r != OGS_ERROR);
-                    } else if (!(mme_ue->tracking_area_update_request_presencemask &
-                                OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE)) {
-                        ogs_info("[%s] TAU accept(NO Bearer Context Status)",
                                 mme_ue->imsi_bcd);
+                    }
+
+                    /* check BCS regardless of active_flag */
+                    if (mme_ue->tracking_area_update_request_presencemask &
+                        OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE) {
+                        ogs_info("[%s] TAU accept(active_flag=%d, BCS check)",
+                            mme_ue->imsi_bcd,
+                            mme_ue->nas_eps.update.active_flag);
+                        mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
+                    } else {
+                        ogs_info("[%s] TAU accept(active_flag=%d, No BCS)",
+                            mme_ue->imsi_bcd,
+                            mme_ue->nas_eps.update.active_flag);
                         r = nas_eps_send_tau_accept(mme_ue,
+                                mme_ue->nas_eps.update.active_flag ?
+                                S1AP_ProcedureCode_id_InitialContextSetup :
                                 S1AP_ProcedureCode_id_downlinkNASTransport);
                         ogs_expect(r == OGS_OK);
                         ogs_assert(r != OGS_ERROR);
-                    } else {
-                        ogs_info("[%s] TAU accept(WITH Bearer Context Status)",
-                                mme_ue->imsi_bcd);
-                        mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
                     }
                 } else if (e->s1ap_code ==
                         S1AP_ProcedureCode_id_uplinkNASTransport) {

src/mme/mme-path.c

@@ -329,7 +329,7 @@ cleanup:
 /* ----------------------------------------------------------------------
  * Function: mme_send_delete_session_or_tau_accept
  * ----------------------------------------------------------------------
- * - If active_flag == 0, check UE's EPS Bearer Context Status (BCS)
+ * - Check UE's EPS Bearer Context Status (BCS) regardless of active_flag
  *   against MME's sessions before sending TAU ACCEPT.
  * - If UE does not report the default bearer EBI, delete that session.
  * - Otherwise, send TAU ACCEPT immediately.
@@ -383,11 +383,21 @@ void mme_send_delete_session_or_tau_accept(enb_ue_t *enb_ue, mme_ue_t *mme_ue)
     }
 
     if (deleted > 0) {
-        ogs_warn("[%s] Deleted %d session(s) due to BCS mismatch",
+        ogs_warn("[%s] Deleted %d session(s) due to BCS mismatch, "
-                mme_ue->imsi_bcd, deleted);
+                "active_flag=%d",
+                mme_ue->imsi_bcd, deleted,
+                mme_ue->nas_eps.update.active_flag);
     } else {
-        ogs_info("[%s] TAU accept(BCS match)", mme_ue->imsi_bcd);
+        /*
+         * Choose S1AP procedure based on active_flag:
+         *  - active_flag==1 : InitialContextSetup
+         *  - active_flag==0 : DownlinkNASTransport
+         */
+        ogs_info("[%s] Send TAU accept(BCS match, active_flag=%d)",
+                 mme_ue->imsi_bcd, mme_ue->nas_eps.update.active_flag);
         r = nas_eps_send_tau_accept(mme_ue,
+                mme_ue->nas_eps.update.active_flag ?
+                S1AP_ProcedureCode_id_InitialContextSetup :
                 S1AP_ProcedureCode_id_downlinkNASTransport);
         ogs_expect(r == OGS_OK);
         ogs_assert(r != OGS_ERROR);

src/mme/mme-s11-handler.c

@@ -886,8 +886,11 @@ void mme_s11_handle_delete_session_response(
 
         GTP_COUNTER_CHECK(mme_ue, GTP_COUNTER_DELETE_SESSION_BY_TAU,
 
-            ogs_info("[%s] TAU accept(BCS mismatch)", mme_ue->imsi_bcd);
+            ogs_info("[%s] Send TAU accept(BCS match, active_flag=%d)",
+                     mme_ue->imsi_bcd, mme_ue->nas_eps.update.active_flag);
             r = nas_eps_send_tau_accept(mme_ue,
+                    mme_ue->nas_eps.update.active_flag ?
+                    S1AP_ProcedureCode_id_InitialContextSetup :
                     S1AP_ProcedureCode_id_downlinkNASTransport);
             ogs_expect(r == OGS_OK);
             ogs_assert(r != OGS_ERROR);

src/mme/sgsap-handler.c

@@ -150,25 +150,26 @@ void sgsap_handle_location_update_accept(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
                 ogs_kdf_nh_enb(mme_ue->kasme, mme_ue->kenb, mme_ue->nh);
                 mme_ue->nhcc = 1;
 
-                ogs_info("[%s] LU accept + TAU accept(active_flag==1)",
+                ogs_info("[%s] KDF update(active_flag=1)", mme_ue->imsi_bcd);
-                        mme_ue->imsi_bcd);
+            }
-                r = nas_eps_send_tau_accept(mme_ue,
+
-                        S1AP_ProcedureCode_id_InitialContextSetup);
+            /* check BCS regardless of active_flag */
-                ogs_expect(r == OGS_OK);
+            if (mme_ue->tracking_area_update_request_presencemask &
-                ogs_assert(r != OGS_ERROR);
+                OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE) {
-            } else if (!(mme_ue->tracking_area_update_request_presencemask &
+                ogs_info("[%s] LU accept + TAU accept(active_flag=%d, BCS)",
-                        OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE)) {
+                    mme_ue->imsi_bcd,
-                ogs_info("[%s] LU accept + TAU accept(NO Bearer Context Status)",
+                    mme_ue->nas_eps.update.active_flag);
-                        mme_ue->imsi_bcd);
+                mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
+            } else {
+                ogs_info("[%s] LU accept + TAU accept(active_flag=%d, No BCS)",
+                    mme_ue->imsi_bcd,
+                    mme_ue->nas_eps.update.active_flag);
                 r = nas_eps_send_tau_accept(mme_ue,
+                        mme_ue->nas_eps.update.active_flag ?
+                        S1AP_ProcedureCode_id_InitialContextSetup :
                         S1AP_ProcedureCode_id_downlinkNASTransport);
                 ogs_expect(r == OGS_OK);
                 ogs_assert(r != OGS_ERROR);
-            } else {
-                ogs_info("[%s] LU accept + TAU accept"
-                        "(WITH Bearer Context Status)",
-                        mme_ue->imsi_bcd);
-                mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
             }
         } else if (mme_ue->tracking_area_update_request_type ==
                 MME_TAU_TYPE_UPLINK_NAS_TRANPORT) {
@@ -359,31 +360,30 @@ void sgsap_handle_location_update_reject(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
                 ogs_kdf_nh_enb(mme_ue->kasme, mme_ue->kenb, mme_ue->nh);
                 mme_ue->nhcc = 1;
 
-                ogs_fatal("[%s] LU reject + TAU accept(active_flag==1)",
+                ogs_info("[%s] KDF update(active_flag=1)", mme_ue->imsi_bcd);
-                        mme_ue->imsi_bcd);
+            }
-                r = nas_eps_send_tau_accept(mme_ue,
+
-                        S1AP_ProcedureCode_id_InitialContextSetup);
+            /* check BCS regardless of active_flag */
-                ogs_expect(r == OGS_OK);
+            if (mme_ue->tracking_area_update_request_presencemask &
-                ogs_assert(r != OGS_ERROR);
+                OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE) {
-            } else if (!(mme_ue->tracking_area_update_request_presencemask &
+                ogs_info("[%s] LU reject + TAU accept(active_flag=%d, BCS)",
-                        OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_EPS_BEARER_CONTEXT_STATUS_TYPE)) {
+                    mme_ue->imsi_bcd,
-                ogs_fatal("[%s] LU reject + TAU accept"
+                    mme_ue->nas_eps.update.active_flag);
-                        "(NO Bearer Context Status)",
+                mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
-                        mme_ue->imsi_bcd);
+            } else {
+                ogs_info("[%s] LU reject + TAU accept(active_flag=%d, No BCS)",
+                    mme_ue->imsi_bcd,
+                    mme_ue->nas_eps.update.active_flag);
                 r = nas_eps_send_tau_accept(mme_ue,
+                        mme_ue->nas_eps.update.active_flag ?
+                        S1AP_ProcedureCode_id_InitialContextSetup :
                         S1AP_ProcedureCode_id_downlinkNASTransport);
                 ogs_expect(r == OGS_OK);
                 ogs_assert(r != OGS_ERROR);
-            } else {
-                ogs_fatal("[%s] LU reject + TAU accept"
-                        "(WITH Bearer Context Status)",
-                        mme_ue->imsi_bcd);
-                mme_send_delete_session_or_tau_accept(enb_ue, mme_ue);
             }
         } else if (mme_ue->tracking_area_update_request_type ==
                 MME_TAU_TYPE_UPLINK_NAS_TRANPORT) {
-            ogs_debug("    Uplink NAS Transport");
+            ogs_info("[%s] LU reject + TAU accept(UplinkNASTransport)",
-            ogs_fatal("[%s] LU reject + TAU accept(UplinkNASTransport)",
                     mme_ue->imsi_bcd);
             r = nas_eps_send_tau_accept(mme_ue,
                     S1AP_ProcedureCode_id_downlinkNASTransport);
@@ -391,9 +391,8 @@ void sgsap_handle_location_update_reject(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
             ogs_assert(r != OGS_ERROR);
         } else if (mme_ue->tracking_area_update_request_type ==
                 MME_TAU_TYPE_UNPROTECTED_INTEGRITY) {
-            ogs_fatal("[%s] LU reject + TAU accept(Unprotected Integrity)",
+            ogs_info("[%s] LU reject + TAU accept(Unprotected Integrity)",
                     mme_ue->imsi_bcd);
-            ogs_debug("    Unprotected Integrity");
             r = nas_eps_send_tau_accept(mme_ue,
                     S1AP_ProcedureCode_id_InitialContextSetup);
             ogs_expect(r == OGS_OK);
@@ -414,7 +413,6 @@ void sgsap_handle_location_update_reject(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
          */
         if (!mme_ue->nas_eps.update.active_flag &&
             !MME_NEXT_P_TMSI_IS_AVAILABLE(mme_ue)) {
-            ogs_fatal("NEXT = %d", MME_NEXT_P_TMSI_IS_AVAILABLE(mme_ue));
             enb_ue->relcause.group = S1AP_Cause_PR_nas;
             enb_ue->relcause.cause = S1AP_CauseNas_normal_release;
             mme_send_release_access_bearer_or_ue_context_release(enb_ue);