diff --git a/lib/diameter/s6b/message.h b/lib/diameter/s6b/message.h
index d33ef167e..25e19e26d 100644
--- a/lib/diameter/s6b/message.h
+++ b/lib/diameter/s6b/message.h
@@ -34,6 +34,14 @@ extern struct dict_object *ogs_diam_s6b_application;
 
 extern struct dict_object *ogs_diam_s6b_mip6_feature_vector;
 
+typedef struct ogs_diam_s6b_message_s {
+#define OGS_DIAM_S6B_CMD_SESSION_TERMINATION                        1
+    uint16_t            cmd_code;
+    uint32_t            result_code;
+    uint32_t            *err;
+    uint32_t            *exp_err;
+} ogs_diam_s6b_message_t;
+
 int ogs_diam_s6b_init(void);
 
 #ifdef __cplusplus
diff --git a/src/smf/context.h b/src/smf/context.h
index a5c2c071f..70a5dddda 100644
--- a/src/smf/context.h
+++ b/src/smf/context.h
@@ -214,7 +214,13 @@ typedef struct smf_sess_s {
         bool gx_ccr_init_in_flight; /* Waiting for Gx CCA */
         uint32_t gx_cca_init_err; /* Gx CCA RXed error code */
         bool gy_ccr_init_in_flight; /* Waiting for Gy CCA */
-        uint32_t gy_cca_init_err; /* Gx CCA RXed error code */
+        uint32_t gy_cca_init_err; /* Gy CCA RXed error code */
+        bool gx_ccr_term_in_flight; /* Waiting for Gx CCA */
+        uint32_t gx_cca_term_err; /* Gx CCA RXed error code */
+        bool gy_ccr_term_in_flight; /* Waiting for Gy CCA */
+        uint32_t gy_cca_term_err; /* Gy CCA RXed error code */
+        bool s6b_str_in_flight; /* Waiting for S6B CCA */
+        uint32_t s6b_sta_err; /* S6B CCA RXed error code */
     } sm_data;
 
     ogs_pfcp_sess_t pfcp;           /* PFCP session context */
diff --git a/src/smf/event.c b/src/smf/event.c
index 181aa0cc3..8dd6dea4f 100644
--- a/src/smf/event.c
+++ b/src/smf/event.c
@@ -64,6 +64,8 @@ const char *smf_event_get_name(smf_event_t *e)
 
     case SMF_EVT_S5C_MESSAGE:
         return "SMF_EVT_S5C_MESSAGE";
+    case SMF_EVT_S6B_MESSAGE:
+        return "SMF_EVT_S6B_MESSAGE";
     case SMF_EVT_GN_MESSAGE:
         return "SMF_EVT_GN_MESSAGE";
     case SMF_EVT_GX_MESSAGE:
diff --git a/src/smf/event.h b/src/smf/event.h
index 3f8831e30..36c700c7b 100644
--- a/src/smf/event.h
+++ b/src/smf/event.h
@@ -34,6 +34,7 @@ typedef struct ogs_pfcp_xact_s ogs_pfcp_xact_t;
 typedef struct ogs_pfcp_message_s ogs_pfcp_message_t;
 typedef struct ogs_diam_gx_message_s ogs_diam_gx_message_t;
 typedef struct ogs_diam_gy_message_s ogs_diam_gy_message_t;
+typedef struct ogs_diam_s6b_message_s ogs_diam_s6b_message_t;
 typedef struct smf_sess_s smf_sess_t;
 typedef struct smf_upf_s smf_upf_t;
 typedef struct ogs_sbi_request_s ogs_sbi_request_t;
@@ -48,6 +49,7 @@ typedef enum {
     SMF_EVT_BASE = OGS_FSM_USER_SIG,
 
     SMF_EVT_S5C_MESSAGE,
+    SMF_EVT_S6B_MESSAGE,
     SMF_EVT_GN_MESSAGE,
     SMF_EVT_GX_MESSAGE,
     SMF_EVT_GY_MESSAGE,
@@ -90,6 +92,7 @@ typedef struct smf_event_s {
     union {
         ogs_diam_gx_message_t *gx_message;
         ogs_diam_gy_message_t *gy_message;
+        ogs_diam_s6b_message_t *s6b_message;
     };
 
     struct {
diff --git a/src/smf/gn-handler.c b/src/smf/gn-handler.c
index 83d6ce2ff..d96cc27f0 100644
--- a/src/smf/gn-handler.c
+++ b/src/smf/gn-handler.c
@@ -239,39 +239,20 @@ uint8_t smf_gn_handle_create_pdp_context_request(
     return cause_value;
 }
 
-void smf_gn_handle_delete_pdp_context_request(
+uint8_t smf_gn_handle_delete_pdp_context_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp1_delete_pdp_context_request_t *req)
 {
-    uint8_t cause_value = 0;
-
     ogs_debug("Delete PDP Context Request");
 
-    ogs_assert(xact);
-    ogs_assert(req);
-
-    cause_value = OGS_GTP1_CAUSE_REQUEST_ACCEPTED;
-
-    if (!sess) {
-        ogs_warn("No Context");
-        cause_value = OGS_GTP1_CAUSE_NON_EXISTENT;
-    } else {
-        if (!ogs_diam_app_connected(OGS_DIAM_GX_APPLICATION_ID)) {
-            ogs_error("No Gx Diameter Peer");
-            cause_value = OGS_GTP1_CAUSE_NO_RESOURCES_AVAILABLE;
-        }
-    }
-
-    if (cause_value != OGS_GTP1_CAUSE_REQUEST_ACCEPTED) {
-        ogs_gtp1_send_error_message(xact, sess ? sess->sgw_s5c_teid : 0,
-                OGS_GTP1_DELETE_PDP_CONTEXT_RESPONSE_TYPE, cause_value);
-        return;
+    if (!ogs_diam_app_connected(OGS_DIAM_GX_APPLICATION_ID)) {
+        ogs_error("No Gx Diameter Peer");
+        return OGS_GTP1_CAUSE_NO_RESOURCES_AVAILABLE;
     }
 
     ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
             sess->sgw_s5c_teid, sess->smf_n4_teid);
-    smf_gx_send_ccr(sess, xact,
-        OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST);
+    return OGS_GTP1_CAUSE_REQUEST_ACCEPTED;
 }
 
 void smf_gn_handle_update_pdp_context_request(
diff --git a/src/smf/gn-handler.h b/src/smf/gn-handler.h
index 8e8f42e63..df1b60e62 100644
--- a/src/smf/gn-handler.h
+++ b/src/smf/gn-handler.h
@@ -35,7 +35,7 @@ void smf_gn_handle_echo_response(
 uint8_t smf_gn_handle_create_pdp_context_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp1_create_pdp_context_request_t *req);
-void smf_gn_handle_delete_pdp_context_request(
+uint8_t smf_gn_handle_delete_pdp_context_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp1_delete_pdp_context_request_t *req);
 void smf_gn_handle_update_pdp_context_request(
diff --git a/src/smf/gsm-sm.c b/src/smf/gsm-sm.c
index b57fdf86e..3af373dfc 100644
--- a/src/smf/gsm-sm.c
+++ b/src/smf/gsm-sm.c
@@ -76,6 +76,16 @@ static void send_gtp_create_err_msg(const smf_sess_t *sess, ogs_gtp_xact_t *gtp_
             OGS_GTP2_CREATE_SESSION_RESPONSE_TYPE, gtp_cause);
 }
 
+static void send_gtp_delete_err_msg(const smf_sess_t *sess, ogs_gtp_xact_t *gtp_xact, uint8_t gtp_cause)
+{
+    if (gtp_xact->gtp_version == 1)
+        ogs_gtp1_send_error_message(gtp_xact, sess->sgw_s5c_teid,
+            OGS_GTP1_DELETE_PDP_CONTEXT_RESPONSE_TYPE, gtp_cause);
+    else
+        ogs_gtp2_send_error_message(gtp_xact, sess->sgw_s5c_teid,
+            OGS_GTP2_DELETE_SESSION_RESPONSE_TYPE, gtp_cause);
+}
+
 static bool send_ccr_init_req_gx_gy(smf_sess_t *sess, smf_event_t *e)
 {
     int use_gy = smf_use_gy_iface();
@@ -103,6 +113,41 @@ static bool send_ccr_init_req_gx_gy(smf_sess_t *sess, smf_event_t *e)
     return true;
 }
 
+static bool send_ccr_termination_req_gx_gy_s6b(smf_sess_t *sess, smf_event_t *e)
+{
+    /* TODO: we should take into account here whether "sess" has an active Gy
+       session created, not whether one was supposedly created as per policy */
+    int use_gy = smf_use_gy_iface();
+
+    if (use_gy == -1) {
+        ogs_error("No Gy Diameter Peer");
+        /* TODO: drop Gx connection here, possibly move to another "releasing" state! */
+        uint8_t gtp_cause = (e->gtp_xact->gtp_version == 1) ?
+                        OGS_GTP1_CAUSE_NO_RESOURCES_AVAILABLE :
+                        OGS_GTP2_CAUSE_UE_NOT_AUTHORISED_BY_OCS_OR_EXTERNAL_AAA_SERVER;
+        send_gtp_delete_err_msg(sess, e->gtp_xact, gtp_cause);
+        return false;
+    }
+
+    if (sess->gtp_rat_type == OGS_GTP2_RAT_TYPE_WLAN) {
+        sess->sm_data.s6b_str_in_flight = true;
+        smf_s6b_send_str(sess, e->gtp_xact,
+            OGS_DIAM_TERMINATION_CAUSE_DIAMETER_LOGOUT);
+    }
+
+    sess->sm_data.gx_ccr_term_in_flight = true;
+    smf_gx_send_ccr(sess, e->gtp_xact,
+        OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST);
+
+    if (use_gy == 1) {
+        /* Gy is available, set up session for the bearer before accepting it towards the UE */
+        sess->sm_data.gy_ccr_term_in_flight = true;
+        smf_gy_send_ccr(sess, e->gtp_xact,
+            OGS_DIAM_GY_CC_REQUEST_TYPE_TERMINATION_REQUEST);
+    }
+    return true;
+}
+
 void smf_gsm_state_initial(ogs_fsm_t *s, smf_event_t *e)
 {
     ogs_assert(s);
@@ -110,6 +155,8 @@ void smf_gsm_state_initial(ogs_fsm_t *s, smf_event_t *e)
     smf_sess_t *sess = e->sess;
     uint8_t gtp1_cause, gtp2_cause;
 
+    smf_sm_debug(e);
+
     switch (e->id) {
     case OGS_FSM_ENTRY_SIG:
         /* reset state: */
@@ -171,6 +218,8 @@ void smf_gsm_state_initial_wait_auth(ogs_fsm_t *s, smf_event_t *e)
     smf_sess_t *sess = e->sess;
     uint32_t diam_err;
 
+    smf_sm_debug(e);
+
     switch (e->id) {
     case SMF_EVT_GX_MESSAGE:
         switch(e->gx_message->cmd_code) {
@@ -235,6 +284,8 @@ void smf_gsm_state_initial_wait_pfcp_establishment(ogs_fsm_t *s, smf_event_t *e)
     smf_sess_t *sess = e->sess;
     uint8_t pfcp_cause, gtp_cause;
 
+    smf_sm_debug(e);
+
     switch (e->id) {
     case SMF_EVT_N4_MESSAGE:
         switch (e->pfcp_message->h.type) {
@@ -322,6 +373,8 @@ void smf_gsm_state_operational(ogs_fsm_t *s, smf_event_t *e)
 
     smf_n1_n2_message_transfer_param_t param;
     uint8_t pfcp_cause;
+    uint8_t gtp1_cause, gtp2_cause;
+    bool release;
 
     int state = 0;
 
@@ -340,6 +393,44 @@ void smf_gsm_state_operational(ogs_fsm_t *s, smf_event_t *e)
     case OGS_FSM_EXIT_SIG:
         break;
 
+    case SMF_EVT_GN_MESSAGE:
+        switch(e->gtp1_message->h.type) {
+        case OGS_GTP1_DELETE_PDP_CONTEXT_REQUEST_TYPE:
+            gtp1_cause = smf_gn_handle_delete_pdp_context_request(sess,
+                            e->gtp_xact,
+                            &e->gtp1_message->delete_pdp_context_request);
+            if (gtp1_cause != OGS_GTP1_CAUSE_REQUEST_ACCEPTED) {
+                ogs_gtp1_send_error_message(e->gtp_xact, sess->sgw_s5c_teid,
+                        OGS_GTP1_DELETE_PDP_CONTEXT_RESPONSE_TYPE, gtp1_cause);
+                return;
+            }
+            OGS_FSM_TRAN(s, &smf_gsm_state_release_wait_pfcp_deletion);
+        }
+        break;
+
+    case SMF_EVT_S5C_MESSAGE:
+        switch(e->gtp2_message->h.type) {
+        case OGS_GTP2_DELETE_SESSION_REQUEST_TYPE:
+            gtp2_cause = smf_s5c_handle_delete_session_request(sess, e->gtp_xact,
+                            &e->gtp2_message->delete_session_request);
+            if (gtp2_cause != OGS_GTP2_CAUSE_REQUEST_ACCEPTED) {
+                ogs_gtp2_send_error_message(e->gtp_xact, sess->sgw_s5c_teid,
+                        OGS_GTP2_DELETE_SESSION_RESPONSE_TYPE, gtp2_cause);
+                return;
+            }
+            OGS_FSM_TRAN(s, &smf_gsm_state_release_wait_pfcp_deletion);
+            break;
+        case OGS_GTP2_DELETE_BEARER_RESPONSE_TYPE:
+            release = smf_s5c_handle_delete_bearer_response(
+                sess, e->gtp_xact, &e->gtp2_message->delete_bearer_response);
+            if (release) {
+                e->gtp_xact = NULL;
+                OGS_FSM_TRAN(s, &smf_gsm_state_release_wait_pfcp_deletion);
+            }
+            break;
+        }
+        break;
+
     case SMF_EVT_N4_MESSAGE:
         switch (e->pfcp_message->h.type) {
         case OGS_PFCP_SESSION_ESTABLISHMENT_RESPONSE_TYPE:
@@ -361,6 +452,14 @@ void smf_gsm_state_operational(ogs_fsm_t *s, smf_event_t *e)
             ogs_assert(param.n2smbuf);
             smf_namf_comm_send_n1_n2_message_transfer(sess, &param);
             break;
+        case OGS_PFCP_SESSION_DELETION_RESPONSE_TYPE:
+            /* This is left here for 5gc sessions to properly receive messages,
+               since tear down transitions are not implemented yet for 5gc
+               sessions. See #if0 in smf_gsm_state_initial_wait_pfcp_deletion() */
+            assert(!e->pfcp_xact->epc);
+            smf_5gc_n4_handle_session_deletion_response(sess,
+                    e->pfcp_xact, &e->pfcp_message->pfcp_session_deletion_response);
+            break;
         }
         break;
 
@@ -743,6 +842,171 @@ void smf_gsm_state_operational(ogs_fsm_t *s, smf_event_t *e)
     }
 }
 
+void smf_gsm_state_release_wait_pfcp_deletion(ogs_fsm_t *s, smf_event_t *e)
+{
+    smf_sess_t *sess = NULL;
+    uint8_t pfcp_cause, gtp_cause;
+    ogs_gtp_xact_t *gtp_xact;
+    ogs_assert(s);
+    ogs_assert(e);
+
+    smf_sm_debug(e);
+
+    sess = e->sess;
+    ogs_assert(sess);
+
+    switch (e->id) {
+    case OGS_FSM_ENTRY_SIG:
+        ogs_assert(OGS_OK ==
+            smf_epc_pfcp_send_session_deletion_request(sess, e->gtp_xact));
+        break;
+
+    case OGS_FSM_EXIT_SIG:
+        break;
+
+    case SMF_EVT_GN_MESSAGE:
+    case SMF_EVT_S5C_MESSAGE:
+        break; /* ignore */
+
+    case SMF_EVT_N4_MESSAGE:
+        gtp_xact = e->pfcp_xact->assoc_xact;
+        switch (e->pfcp_message->h.type) {
+        case OGS_PFCP_SESSION_DELETION_RESPONSE_TYPE:
+            if (e->pfcp_xact->epc) {
+                gtp_xact = e->pfcp_xact->assoc_xact;
+                pfcp_cause = smf_epc_n4_handle_session_deletion_response(sess,
+                        e->pfcp_xact, &e->pfcp_message->pfcp_session_deletion_response);
+                if (pfcp_cause != OGS_PFCP_CAUSE_REQUEST_ACCEPTED) {
+                    /* FIXME: tear down Gy and Gx */
+                    gtp_cause = gtp_cause_from_pfcp(pfcp_cause, gtp_xact->gtp_version);
+                    send_gtp_delete_err_msg(sess, gtp_xact, gtp_cause);
+                    return;
+                }
+                e->gtp_xact = gtp_xact;
+                if (send_ccr_termination_req_gx_gy_s6b(sess, e) == true)
+                    OGS_FSM_TRAN(s, &smf_gsm_state_release_wait_auth);
+                /* else: free session? */
+            } else {
+#if 0
+                /* This is currently not happening, since 5gc isn't yet properly
+                   integrated and doesn't move to this state */
+                smf_5gc_n4_handle_session_deletion_response(sess,
+                        e->pfcp_xact, &message->pfcp_session_deletion_response);
+                return; /* TODO: implement handling of errors here */
+#endif
+            }
+            break;
+        }
+        return;
+
+    default:
+        ogs_error("Unknown event %s", smf_event_get_name(e));
+        break;
+    }
+}
+
+void smf_gsm_state_release_wait_auth(ogs_fsm_t *s, smf_event_t *e)
+{
+    ogs_assert(e && e->sess);
+    smf_sess_t *sess = e->sess;
+    uint32_t diam_err;
+
+    smf_sm_debug(e);
+
+    switch (e->id) {
+    case OGS_FSM_ENTRY_SIG:
+        /* reset state: */
+        sess->sm_data.gx_cca_term_err = ER_DIAMETER_SUCCESS;
+        sess->sm_data.gy_cca_term_err = ER_DIAMETER_SUCCESS;
+        sess->sm_data.s6b_sta_err = ER_DIAMETER_SUCCESS;
+        break;
+
+    case SMF_EVT_GN_MESSAGE:
+    case SMF_EVT_S5C_MESSAGE:
+    case SMF_EVT_N4_MESSAGE:
+        break; /* ignore */
+
+    case SMF_EVT_GX_MESSAGE:
+        switch(e->gx_message->cmd_code) {
+        case OGS_DIAM_GX_CMD_CODE_CREDIT_CONTROL:
+            switch(e->gx_message->cc_request_type) {
+            case OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST:
+                diam_err = smf_gx_handle_cca_termination_request(sess,
+                                e->gx_message, e->gtp_xact);
+                sess->sm_data.gx_ccr_term_in_flight = false;
+                sess->sm_data.gx_cca_term_err = diam_err;
+                goto test_can_proceed;
+            }
+            break;
+        }
+        break;
+
+    case SMF_EVT_GY_MESSAGE:
+        switch(e->gy_message->cmd_code) {
+        case OGS_DIAM_GY_CMD_CODE_CREDIT_CONTROL:
+            switch(e->gy_message->cc_request_type) {
+            case OGS_DIAM_GY_CC_REQUEST_TYPE_TERMINATION_REQUEST:
+                ogs_assert(e->gtp_xact);
+                diam_err = smf_gy_handle_cca_termination_request(sess,
+                                e->gy_message, e->gtp_xact);
+                sess->sm_data.gy_ccr_term_in_flight = false;
+                sess->sm_data.gy_cca_term_err = diam_err;
+                goto test_can_proceed;
+            }
+            break;
+        }
+        break;
+
+    case SMF_EVT_S6B_MESSAGE:
+        switch(e->s6b_message->cmd_code) {
+        case OGS_DIAM_S6B_CMD_SESSION_TERMINATION:
+            sess->sm_data.s6b_str_in_flight = false;
+            /* TODO: validate error code from message below: */
+            sess->sm_data.s6b_sta_err = ER_DIAMETER_SUCCESS;
+            goto test_can_proceed;
+        }
+        break;
+    }
+    return;
+
+test_can_proceed:
+    /* First wait for both Gx and Gy requests to be done: */
+    if (!sess->sm_data.gx_ccr_term_in_flight &&
+        !sess->sm_data.gy_ccr_term_in_flight &&
+        !sess->sm_data.s6b_str_in_flight) {
+        diam_err = ER_DIAMETER_SUCCESS;
+        if (sess->sm_data.gx_cca_term_err != ER_DIAMETER_SUCCESS)
+            diam_err = sess->sm_data.gx_cca_term_err;
+        if (sess->sm_data.gy_cca_term_err != ER_DIAMETER_SUCCESS)
+            diam_err = sess->sm_data.gy_cca_term_err;
+        if (sess->sm_data.s6b_sta_err != ER_DIAMETER_SUCCESS)
+            diam_err = sess->sm_data.s6b_sta_err;
+
+        /* Initiated by peer request, let's answer: */
+        if (e->gtp_xact) {
+            if (diam_err == ER_DIAMETER_SUCCESS) {
+                /*
+                 * 1. MME sends Delete Session Request to SGW/SMF.
+                 * 2. SMF sends Delete Session Response to SGW/MME.
+                 */
+                switch (e->gtp_xact->gtp_version) {
+                case 1:
+                    ogs_assert(OGS_OK == smf_gtp1_send_delete_pdp_context_response(sess, e->gtp_xact));
+                    break;
+                case 2:
+                    ogs_assert(OGS_OK == smf_gtp_send_delete_session_response(sess, e->gtp_xact));
+                    break;
+                }
+            } else {
+                uint8_t gtp_cause = gtp_cause_from_diameter(e->gtp_xact->gtp_version,
+                                diam_err, NULL);
+                send_gtp_delete_err_msg(sess, e->gtp_xact, gtp_cause);
+            }
+        }
+        OGS_FSM_TRAN(s, &smf_gsm_state_session_will_release);
+    }
+}
+
 void smf_gsm_state_session_will_release(ogs_fsm_t *s, smf_event_t *e)
 {
     smf_sess_t *sess = NULL;
@@ -756,6 +1020,7 @@ void smf_gsm_state_session_will_release(ogs_fsm_t *s, smf_event_t *e)
 
     switch (e->id) {
     case OGS_FSM_ENTRY_SIG:
+        SMF_SESS_CLEAR(sess);
         break;
 
     case OGS_FSM_EXIT_SIG:
diff --git a/src/smf/gx-handler.c b/src/smf/gx-handler.c
index 27bab4890..90719a4ce 100644
--- a/src/smf/gx-handler.c
+++ b/src/smf/gx-handler.c
@@ -243,26 +243,18 @@ uint32_t smf_gx_handle_cca_initial_request(
     return ER_DIAMETER_SUCCESS;
 }
 
-void smf_gx_handle_cca_termination_request(
+uint32_t smf_gx_handle_cca_termination_request(
         smf_sess_t *sess, ogs_diam_gx_message_t *gx_message,
         ogs_gtp_xact_t *gtp_xact)
 {
     ogs_assert(sess);
     ogs_assert(gx_message);
-    ogs_assert(gtp_xact);
 
     ogs_debug("[SMF] Delete Session Response");
     ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
             sess->sgw_s5c_teid, sess->smf_n4_teid);
 
-    /*
-     * << 'gtp_xact' is NOT NULL >>
-     *
-     * 1. MME sends Delete Session Request to SGW/SMF.
-     * 2. SMF sends Delete Session Response to SGW/MME.
-     */
-    ogs_assert(OGS_OK ==
-        smf_epc_pfcp_send_session_deletion_request(sess, gtp_xact));
+    return ER_DIAMETER_SUCCESS;
 }
 
 void smf_gx_handle_re_auth_request(
diff --git a/src/smf/gx-handler.h b/src/smf/gx-handler.h
index 99a0bd921..38066c37d 100644
--- a/src/smf/gx-handler.h
+++ b/src/smf/gx-handler.h
@@ -29,7 +29,7 @@ extern "C" {
 uint32_t smf_gx_handle_cca_initial_request(
         smf_sess_t *sess, ogs_diam_gx_message_t *gx_message,
         ogs_gtp_xact_t *gtp_xact);
-void smf_gx_handle_cca_termination_request(
+uint32_t smf_gx_handle_cca_termination_request(
         smf_sess_t *sess, ogs_diam_gx_message_t *gx_message,
         ogs_gtp_xact_t *gtp_xact);
 void smf_gx_handle_re_auth_request(
diff --git a/src/smf/gx-path.c b/src/smf/gx-path.c
index ed9e1ef72..8f260b518 100644
--- a/src/smf/gx-path.c
+++ b/src/smf/gx-path.c
@@ -93,7 +93,6 @@ void smf_gx_send_ccr(smf_sess_t *sess, ogs_gtp_xact_t *xact,
     struct sockaddr_in6 sin6;
     uint32_t charing_id;
 
-    ogs_assert(xact);
     ogs_assert(sess);
 
     ogs_assert(sess->ipv4 || sess->ipv6);
@@ -742,7 +741,6 @@ static void smf_gx_cca_cb(void *data, struct msg **msg)
     ogs_debug("    CC-Request-Number[%d]", cc_request_number);
 
     xact = sess_data->xact[cc_request_number];
-    ogs_assert(xact);
     sess = sess_data->sess;
     ogs_assert(sess);
 
diff --git a/src/smf/gy-handler.c b/src/smf/gy-handler.c
index a245b0871..4ea88daf3 100644
--- a/src/smf/gy-handler.c
+++ b/src/smf/gy-handler.c
@@ -182,7 +182,7 @@ void smf_gy_handle_cca_update_request(
     }
 }
 
-void smf_gy_handle_cca_termination_request(
+uint32_t smf_gy_handle_cca_termination_request(
         smf_sess_t *sess, ogs_diam_gy_message_t *gy_message,
         ogs_gtp_xact_t *gtp_xact)
 {
@@ -194,36 +194,7 @@ void smf_gy_handle_cca_termination_request(
     ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
             sess->sgw_s5c_teid, sess->smf_n4_teid);
 
-     if (gtp_xact) {
-         /*
-          * 1. MME sends Delete Session Request to SGW/SMF.
-          * 2. SMF sends Delete Session Response to SGW/MME.
-          */
-         switch (gtp_xact->gtp_version) {
-         case 1:
-             ogs_assert(OGS_OK == smf_gtp1_send_delete_pdp_context_response(sess, gtp_xact));
-             break;
-         case 2:
-             ogs_assert(OGS_OK == smf_gtp_send_delete_session_response(sess, gtp_xact));
-             break;
-         }
-     } else {
-         /*
-          * 1. SMF sends Delete Bearer Request(DEFAULT BEARER) to SGW/MME.
-          * 2. MME sends Delete Bearer Response to SGW/SMF.
-          *
-          * OR
-          *
-          * 1. SMF sends Delete Bearer Request(DEFAULT BEARER) to ePDG.
-          * 2. ePDG sends Delete Bearer Response(DEFAULT BEARER) to SMF.
-          *
-          * Note that the following messages are not processed here.
-          * - Bearer Resource Command
-          * - Delete Bearer Request/Response with DEDICATED BEARER.
-          */
-     }
-     SMF_SESS_CLEAR(sess);
-     return;
+     return ER_DIAMETER_SUCCESS;
 }
 
 void smf_gy_handle_re_auth_request(
diff --git a/src/smf/gy-handler.h b/src/smf/gy-handler.h
index bc060b65b..7ad47e467 100644
--- a/src/smf/gy-handler.h
+++ b/src/smf/gy-handler.h
@@ -33,7 +33,7 @@ uint32_t smf_gy_handle_cca_initial_request(
 void smf_gy_handle_cca_update_request(
         smf_sess_t *sess, ogs_diam_gy_message_t *gy_message,
         ogs_pfcp_xact_t *gtp_xact);
-void smf_gy_handle_cca_termination_request(
+uint32_t smf_gy_handle_cca_termination_request(
         smf_sess_t *sess, ogs_diam_gy_message_t *gy_message,
         ogs_gtp_xact_t *gtp_xact);
 void smf_gy_handle_re_auth_request(
diff --git a/src/smf/n4-handler.c b/src/smf/n4-handler.c
index 7d5510675..cc885cbf6 100644
--- a/src/smf/n4-handler.c
+++ b/src/smf/n4-handler.c
@@ -693,7 +693,7 @@ void smf_5gc_n4_handle_session_deletion_response(
         ogs_assert(stream);
         ogs_assert(true == ogs_sbi_server_send_response(stream, response));
 
-        SMF_SESS_CLEAR(sess);
+        OGS_FSM_TRAN(&sess->sm, smf_gsm_state_session_will_release);
     } else if (trigger == OGS_PFCP_DELETE_TRIGGER_PCF_INITIATED) {
         smf_n1_n2_message_transfer_param_t param;
 
@@ -1045,61 +1045,28 @@ void smf_epc_n4_handle_session_modification_response(
     }
 }
 
-void smf_epc_n4_handle_session_deletion_response(
+uint8_t smf_epc_n4_handle_session_deletion_response(
         smf_sess_t *sess, ogs_pfcp_xact_t *xact,
         ogs_pfcp_session_deletion_response_t *rsp)
 {
-    uint8_t cause_value = 0;
-    uint8_t resp_type = 0;
-    ogs_gtp_xact_t *gtp_xact = NULL;
     smf_bearer_t *bearer = NULL;
     unsigned int i;
 
+    ogs_assert(sess);
     ogs_assert(xact);
     ogs_assert(rsp);
 
     ogs_debug("Session Deletion Response [epc]");
 
-    gtp_xact = xact->assoc_xact;
-
     ogs_pfcp_xact_commit(xact);
 
-    /* If !gtp_xact, set it to whatever valid, nothing is sent in the end anyway */
-    uint8_t gtp_version = gtp_xact ? gtp_xact->gtp_version : 2;
-
-    if (gtp_version == 1) {
-        resp_type = OGS_GTP1_DELETE_PDP_CONTEXT_RESPONSE_TYPE;
-        cause_value = OGS_GTP1_CAUSE_REQUEST_ACCEPTED;
-    } else {
-        resp_type = OGS_GTP2_DELETE_SESSION_RESPONSE_TYPE;
-        cause_value = OGS_GTP2_CAUSE_REQUEST_ACCEPTED;
-    }
-
-    if (!sess) {
-        ogs_warn("No Context");
-        cause_value = (gtp_version == 1) ?
-                        OGS_GTP1_CAUSE_NON_EXISTENT :
-                        OGS_GTP2_CAUSE_CONTEXT_NOT_FOUND;
-    }
-
-    if (rsp->cause.presence) {
-        if (rsp->cause.u8 != OGS_PFCP_CAUSE_REQUEST_ACCEPTED) {
-            ogs_warn("PFCP Cause[%d] : Not Accepted", rsp->cause.u8);
-            cause_value = gtp_cause_from_pfcp(rsp->cause.u8, gtp_version);
-        }
-    } else {
+    if (!rsp->cause.presence) {
         ogs_error("No Cause");
-        cause_value = (gtp_xact->gtp_version == 1) ?
-                        OGS_GTP1_CAUSE_MANDATORY_IE_MISSING :
-                        OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
+        return OGS_PFCP_CAUSE_MANDATORY_IE_MISSING;
     }
-
-    if (gtp_xact &&
-        ((gtp_version == 1 && cause_value != OGS_GTP1_CAUSE_REQUEST_ACCEPTED) ||
-         (gtp_version == 2 && cause_value != OGS_GTP2_CAUSE_REQUEST_ACCEPTED))) {
-        ogs_gtp_send_error_message(gtp_xact, sess->sgw_s5c_teid, resp_type,
-                cause_value);
-        return;
+    if (rsp->cause.u8 != OGS_PFCP_CAUSE_REQUEST_ACCEPTED) {
+            ogs_warn("PFCP Cause[%d] : Not Accepted", rsp->cause.u8);
+            return rsp->cause.u8;
     }
 
     ogs_assert(sess);
@@ -1124,48 +1091,7 @@ void smf_epc_n4_handle_session_deletion_response(
         sess->gy.duration += use_rep->duration_measurement.u32;
     }
 
-    switch(smf_use_gy_iface()) {
-    case 1:
-        /* Gy is available, terminate the Gy session before terminating it towards the UE */
-        smf_gy_send_ccr(sess, gtp_xact,
-            OGS_DIAM_GY_CC_REQUEST_TYPE_TERMINATION_REQUEST);
-        return;
-    case -1:
-        ogs_error("No Gy Diameter Peer");
-        break; /* continue below */
-    /* default: continue below */
-    }
-
-    if (gtp_xact) {
-        /*
-         * 1. MME sends Delete Session Request to SGW/SMF.
-         * 2. SMF sends Delete Session Response to SGW/MME.
-         */
-        switch (gtp_version) {
-        case 1:
-            ogs_assert(OGS_OK == smf_gtp1_send_delete_pdp_context_response(sess, gtp_xact));
-            break;
-        case 2:
-            ogs_assert(OGS_OK == smf_gtp_send_delete_session_response(sess, gtp_xact));
-            break;
-        }
-    } else {
-        /*
-         * 1. SMF sends Delete Bearer Request(DEFAULT BEARER) to SGW/MME.
-         * 2. MME sends Delete Bearer Response to SGW/SMF.
-         *
-         * OR
-         *
-         * 1. SMF sends Delete Bearer Request(DEFAULT BEARER) to ePDG.
-         * 2. ePDG sends Delete Bearer Response(DEFAULT BEARER) to SMF.
-         *
-         * Note that the following messages are not processed here.
-         * - Bearer Resource Command
-         * - Delete Bearer Request/Response with DEDICATED BEARER.
-         */
-    }
-
-    SMF_SESS_CLEAR(sess);
+    return OGS_PFCP_CAUSE_REQUEST_ACCEPTED;
 }
 
 void smf_n4_handle_session_report_request(
diff --git a/src/smf/n4-handler.h b/src/smf/n4-handler.h
index 0d9708d83..0a610e260 100644
--- a/src/smf/n4-handler.h
+++ b/src/smf/n4-handler.h
@@ -42,7 +42,7 @@ uint8_t smf_epc_n4_handle_session_establishment_response(
 void smf_epc_n4_handle_session_modification_response(
         smf_sess_t *sess, ogs_pfcp_xact_t *xact,
         ogs_pfcp_session_modification_response_t *rsp);
-void smf_epc_n4_handle_session_deletion_response(
+uint8_t smf_epc_n4_handle_session_deletion_response(
         smf_sess_t *sess, ogs_pfcp_xact_t *xact,
         ogs_pfcp_session_deletion_response_t *rsp);
 
diff --git a/src/smf/pfcp-sm.c b/src/smf/pfcp-sm.c
index 0f4b54f96..6425c1a97 100644
--- a/src/smf/pfcp-sm.c
+++ b/src/smf/pfcp-sm.c
@@ -245,17 +245,9 @@ void smf_pfcp_state_associated(ogs_fsm_t *s, smf_event_t *e)
             break;
 
         case OGS_PFCP_SESSION_DELETION_RESPONSE_TYPE:
-            if (!message->h.seid_presence) {
+            if (!message->h.seid_presence)
                 ogs_error("No SEID");
-                break;
-            }
-
-            if (xact->epc)
-                smf_epc_n4_handle_session_deletion_response(
-                    sess, xact, &message->pfcp_session_deletion_response);
-            else
-                smf_5gc_n4_handle_session_deletion_response(
-                    sess, xact, &message->pfcp_session_deletion_response);
+            ogs_fsm_dispatch(&sess->sm, e);
             break;
 
         case OGS_PFCP_SESSION_REPORT_REQUEST_TYPE:
diff --git a/src/smf/s5c-handler.c b/src/smf/s5c-handler.c
index a6fabf340..2cd2cdd61 100644
--- a/src/smf/s5c-handler.c
+++ b/src/smf/s5c-handler.c
@@ -304,58 +304,31 @@ uint8_t smf_s5c_handle_create_session_request(
     return OGS_GTP2_CAUSE_REQUEST_ACCEPTED;
 }
 
-void smf_s5c_handle_delete_session_request(
+uint8_t smf_s5c_handle_delete_session_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_delete_session_request_t *req)
 {
-    uint8_t cause_value = 0;
-
     ogs_debug("Delete Session Request");
 
     ogs_assert(xact);
     ogs_assert(req);
 
-    cause_value = OGS_GTP2_CAUSE_REQUEST_ACCEPTED;
-
-    if (!sess) {
-        ogs_warn("No Context");
-        cause_value = OGS_GTP2_CAUSE_CONTEXT_NOT_FOUND;
-    } else {
-        if (!ogs_diam_app_connected(OGS_DIAM_GX_APPLICATION_ID)) {
-            ogs_error("No Gx Diameter Peer");
-            cause_value = OGS_GTP2_CAUSE_REMOTE_PEER_NOT_RESPONDING;
-        }
-
-        if (sess->gtp_rat_type == OGS_GTP2_RAT_TYPE_WLAN) {
-            if (!ogs_diam_app_connected(OGS_DIAM_S6B_APPLICATION_ID)) {
-                ogs_error("No S6b Diameter Peer");
-                cause_value = OGS_GTP2_CAUSE_REMOTE_PEER_NOT_RESPONDING;
-            }
-        }
+    if (!ogs_diam_app_connected(OGS_DIAM_GX_APPLICATION_ID)) {
+        ogs_error("No Gx Diameter Peer");
+        return OGS_GTP2_CAUSE_REMOTE_PEER_NOT_RESPONDING;
     }
 
-    if (cause_value != OGS_GTP2_CAUSE_REQUEST_ACCEPTED) {
-        ogs_gtp2_send_error_message(xact, sess ? sess->sgw_s5c_teid : 0,
-                OGS_GTP2_DELETE_SESSION_RESPONSE_TYPE, cause_value);
-        return;
+    if (sess->gtp_rat_type == OGS_GTP2_RAT_TYPE_WLAN) {
+        if (!ogs_diam_app_connected(OGS_DIAM_S6B_APPLICATION_ID)) {
+            ogs_error("No S6b Diameter Peer");
+            return OGS_GTP2_CAUSE_REMOTE_PEER_NOT_RESPONDING;
+        }
     }
 
     ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
             sess->sgw_s5c_teid, sess->smf_n4_teid);
 
-    switch (sess->gtp_rat_type) {
-    case OGS_GTP2_RAT_TYPE_EUTRAN:
-        smf_gx_send_ccr(sess, xact,
-            OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST);
-        break;
-    case OGS_GTP2_RAT_TYPE_WLAN:
-        smf_s6b_send_str(sess, xact,
-            OGS_DIAM_TERMINATION_CAUSE_DIAMETER_LOGOUT);
-        break;
-    default:
-        ogs_error("Unknown RAT Type [%d]", sess->gtp_rat_type);
-        ogs_assert_if_reached();
-    }
+    return OGS_GTP2_CAUSE_REQUEST_ACCEPTED;
 }
 
 void smf_s5c_handle_modify_bearer_request(
@@ -664,7 +637,8 @@ void smf_s5c_handle_update_bearer_response(
                 OGS_GTP2_CAUSE_UNDEFINED_VALUE));
 }
 
-void smf_s5c_handle_delete_bearer_response(
+/* return true if entire session must be released */
+bool smf_s5c_handle_delete_bearer_response(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_delete_bearer_response_t *rsp)
 {
@@ -717,66 +691,64 @@ void smf_s5c_handle_delete_bearer_response(
             ogs_error("No Cause");
             cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
         }
+        /* Release entire session: */
+        return true;
+    }
 
-        ogs_assert(OGS_OK ==
-            smf_epc_pfcp_send_session_deletion_request(
-                sess, NULL));
+    /*
+     * 1. MME sends Bearer Resource Command to SGW/SMF.
+     * 2. SMF sends Delete Bearer Request(DEDICATED BEARER) to SGW/MME
+     * 3. MME sends Delete Bearer Response(DEDICATED BEARER) to SGW/SMF
+     *
+     * OR
+     *
+     * 1. SMF sends Delete Bearer Request(DEDICATED BEARER) to SGW/MME
+     * 2. MME sends Delete Bearer Response(DEDICATED BEARER) to SGW/SMF
+     */
+    if (rsp->bearer_contexts.presence == 0) {
+        ogs_error("No Bearer");
+        cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
+    }
+    if (rsp->bearer_contexts.eps_bearer_id.presence == 0) {
+        ogs_error("No EPS Bearer ID");
+        cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
+    }
 
-    } else {
-        /*
-         * 1. MME sends Bearer Resource Command to SGW/SMF.
-         * 2. SMF sends Delete Bearer Request(DEDICATED BEARER) to SGW/MME
-         * 3. MME sends Delete Bearer Response(DEDICATED BEARER) to SGW/SMF
-         *
-         * OR
-         *
-         * 1. SMF sends Delete Bearer Request(DEDICATED BEARER) to SGW/MME
-         * 2. MME sends Delete Bearer Response(DEDICATED BEARER) to SGW/SMF
-         */
-        if (rsp->bearer_contexts.presence == 0) {
-            ogs_error("No Bearer");
-            cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
-        }
-        if (rsp->bearer_contexts.eps_bearer_id.presence == 0) {
-            ogs_error("No EPS Bearer ID");
-            cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
-        }
+    if (rsp->cause.presence) {
+        ogs_gtp2_cause_t *cause = rsp->cause.data;
+        ogs_assert(cause);
 
-        if (rsp->cause.presence) {
-            ogs_gtp2_cause_t *cause = rsp->cause.data;
-            ogs_assert(cause);
+        cause_value = cause->value;
+        if (cause_value == OGS_GTP2_CAUSE_REQUEST_ACCEPTED) {
+            if (rsp->bearer_contexts.cause.presence) {
+                cause = rsp->bearer_contexts.cause.data;
+                ogs_assert(cause);
 
-            cause_value = cause->value;
-            if (cause_value == OGS_GTP2_CAUSE_REQUEST_ACCEPTED) {
-                if (rsp->bearer_contexts.cause.presence) {
-                    cause = rsp->bearer_contexts.cause.data;
-                    ogs_assert(cause);
-
-                    cause_value = cause->value;
-                } else {
-                    ogs_error("No Cause");
-                    cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
-                }
+                cause_value = cause->value;
             } else {
-                ogs_warn("GTP Failed [CAUSE:%d]", cause_value);
+                ogs_error("No Cause");
+                cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
             }
         } else {
-            ogs_error("No Cause");
-            cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
+            ogs_warn("GTP Failed [CAUSE:%d]", cause_value);
         }
-
-        ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
-                sess->sgw_s5c_teid, sess->smf_n4_teid);
-
-        ogs_debug("Delete Bearer Response : SGW[0x%x] --> SMF[0x%x]",
-                sess->sgw_s5c_teid, sess->smf_n4_teid);
-
-        ogs_assert(OGS_OK ==
-            smf_epc_pfcp_send_bearer_modification_request(
-                bearer, NULL, OGS_PFCP_MODIFY_REMOVE,
-                OGS_NAS_PROCEDURE_TRANSACTION_IDENTITY_UNASSIGNED,
-                OGS_GTP2_CAUSE_UNDEFINED_VALUE));
+    } else {
+        ogs_error("No Cause");
+        cause_value = OGS_GTP2_CAUSE_MANDATORY_IE_MISSING;
     }
+
+    ogs_debug("    SGW_S5C_TEID[0x%x] SMF_N4_TEID[0x%x]",
+            sess->sgw_s5c_teid, sess->smf_n4_teid);
+
+    ogs_debug("Delete Bearer Response : SGW[0x%x] --> SMF[0x%x]",
+            sess->sgw_s5c_teid, sess->smf_n4_teid);
+
+    ogs_assert(OGS_OK ==
+        smf_epc_pfcp_send_bearer_modification_request(
+            bearer, NULL, OGS_PFCP_MODIFY_REMOVE,
+            OGS_NAS_PROCEDURE_TRANSACTION_IDENTITY_UNASSIGNED,
+            OGS_GTP2_CAUSE_UNDEFINED_VALUE));
+    return false;
 }
 
 static int reconfigure_packet_filter(smf_pf_t *pf, ogs_gtp2_tft_t *tft, int i)
diff --git a/src/smf/s5c-handler.h b/src/smf/s5c-handler.h
index 1efe28ea4..b45e70199 100644
--- a/src/smf/s5c-handler.h
+++ b/src/smf/s5c-handler.h
@@ -34,7 +34,7 @@ void smf_s5c_handle_echo_response(
 uint8_t smf_s5c_handle_create_session_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_create_session_request_t *req);
-void smf_s5c_handle_delete_session_request(
+uint8_t smf_s5c_handle_delete_session_request(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_delete_session_request_t *req);
 void smf_s5c_handle_modify_bearer_request(
@@ -46,7 +46,7 @@ void smf_s5c_handle_create_bearer_response(
 void smf_s5c_handle_update_bearer_response(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_update_bearer_response_t *req);
-void smf_s5c_handle_delete_bearer_response(
+bool smf_s5c_handle_delete_bearer_response(
         smf_sess_t *sess, ogs_gtp_xact_t *xact,
         ogs_gtp2_delete_bearer_response_t *req);
 void smf_s5c_handle_bearer_resource_command(
diff --git a/src/smf/s6b-path.c b/src/smf/s6b-path.c
index 280860ed6..141e3bad2 100644
--- a/src/smf/s6b-path.c
+++ b/src/smf/s6b-path.c
@@ -20,7 +20,7 @@
 #include "fd-path.h"
 
 static struct session_handler *smf_s6b_reg = NULL;
-static struct disp_hdl *hdl_s6b_fb = NULL; 
+static struct disp_hdl *hdl_s6b_fb = NULL;
 
 struct sess_state {
     smf_sess_t *sess;
@@ -62,12 +62,12 @@ static void state_cleanup(struct sess_state *sess_data, os0_t sid, void *opaque)
     ogs_thread_mutex_unlock(&sess_state_mutex);
 }
 
-static int smf_s6b_fb_cb(struct msg **msg, struct avp *avp, 
+static int smf_s6b_fb_cb(struct msg **msg, struct avp *avp,
         struct session *sess, void *opaque, enum disp_action *act)
 {
 	/* This CB should never be called */
 	ogs_warn("Unexpected message received!");
-	
+
 	return ENOTSUP;
 }
 
@@ -488,7 +488,7 @@ void smf_s6b_send_str(smf_sess_t *sess, ogs_gtp_xact_t *xact, uint32_t cause)
     smf_ue_t *smf_ue = NULL;
     char *user_name = NULL;
 
-    ogs_assert(xact);
+    //ogs_assert(xact);
     ogs_assert(sess);
     smf_ue = sess->smf_ue;
     ogs_assert(smf_ue);
@@ -603,6 +603,7 @@ void smf_s6b_send_str(smf_sess_t *sess, ogs_gtp_xact_t *xact, uint32_t cause)
 static void smf_s6b_sta_cb(void *data, struct msg **msg)
 {
     int ret;
+    int rv;
 
     struct sess_state *sess_data = NULL;
     struct timespec ts;
@@ -612,11 +613,10 @@ static void smf_s6b_sta_cb(void *data, struct msg **msg)
     unsigned long dur;
     int error = 0;
     int new;
-    int result_code = 0;
-    int exp_result_code = 0;
 
+    smf_event_t *e = NULL;
     smf_sess_t *sess = NULL;
-    ogs_gtp_xact_t *xact = NULL;
+    ogs_diam_s6b_message_t *s6b_message = NULL;
 
     ogs_debug("[Session-Termination-Answer]");
 
@@ -638,9 +638,11 @@ static void smf_s6b_sta_cb(void *data, struct msg **msg)
     ogs_debug("    Retrieve its data: [%s]", sess_data->s6b_sid);
 
     sess = sess_data->sess;
-    ogs_assert(sess);
-    xact = sess_data->xact;
-    ogs_assert(xact);
+
+    s6b_message = ogs_calloc(1, sizeof(ogs_diam_s6b_message_t));
+    ogs_assert(s6b_message);
+    /* Set Session Termination Command */
+    s6b_message->cmd_code = OGS_DIAM_S6B_CMD_SESSION_TERMINATION;
 
     /* Value of Result Code */
     ret = fd_msg_search_avp(*msg, ogs_diam_result_code, &avp);
@@ -648,9 +650,10 @@ static void smf_s6b_sta_cb(void *data, struct msg **msg)
     if (avp) {
         ret = fd_msg_avp_hdr(avp, &hdr);
         ogs_assert(ret == 0);
-        result_code = hdr->avp_value->i32;
-        if (result_code != ER_DIAMETER_SUCCESS) {
-            ogs_error("Result Code: %d", result_code);
+        s6b_message->result_code = hdr->avp_value->i32;
+        s6b_message->err = &s6b_message->result_code;
+        if (s6b_message->result_code != ER_DIAMETER_SUCCESS) {
+            ogs_error("Result Code: %d", s6b_message->result_code);
             error++;
         }
     } else {
@@ -665,8 +668,10 @@ static void smf_s6b_sta_cb(void *data, struct msg **msg)
             if (avpch1) {
                 ret = fd_msg_avp_hdr(avpch1, &hdr);
                 ogs_assert(ret == 0);
-                exp_result_code = hdr->avp_value->i32;
-                ogs_error("Experimental Result Code: %d", exp_result_code);
+                s6b_message->result_code = hdr->avp_value->i32;
+                s6b_message->exp_err = &s6b_message->result_code;
+                ogs_error("Experimental Result Code: %d",
+                        s6b_message->result_code);
             }
         } else {
             ogs_error("no Result-Code");
@@ -700,8 +705,21 @@ static void smf_s6b_sta_cb(void *data, struct msg **msg)
     }
 
     if (!error) {
-        smf_gx_send_ccr(sess, xact,
-            OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST);
+        e = smf_event_new(SMF_EVT_S6B_MESSAGE);
+        ogs_assert(e);
+
+        e->sess = sess;
+        e->s6b_message = s6b_message;
+        rv = ogs_queue_push(ogs_app()->queue, e);
+        if (rv != OGS_OK) {
+            ogs_warn("ogs_queue_push() failed:%d", (int)rv);
+            ogs_free(s6b_message);
+            smf_event_free(e);
+        } else {
+            ogs_pollset_notify(ogs_app()->pollset);
+        }
+    } else {
+        ogs_free(s6b_message);
     }
 
     /* Free the message */
diff --git a/src/smf/smf-sm.c b/src/smf/smf-sm.c
index c9c71d495..8c4b7f07d 100644
--- a/src/smf/smf-sm.c
+++ b/src/smf/smf-sm.c
@@ -62,6 +62,7 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
 
     ogs_diam_gx_message_t *gx_message = NULL;
     ogs_diam_gy_message_t *gy_message = NULL;
+    ogs_diam_s6b_message_t *s6b_message = NULL;
 
     ogs_pfcp_node_t *pfcp_node = NULL;
     ogs_pfcp_xact_t *pfcp_xact = NULL;
@@ -145,8 +146,14 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
             ogs_fsm_dispatch(&sess->sm, e);
             break;
         case OGS_GTP2_DELETE_SESSION_REQUEST_TYPE:
-            smf_s5c_handle_delete_session_request(
-                sess, gtp_xact, &gtp2_message.delete_session_request);
+            if (!sess) {
+                ogs_gtp2_send_error_message(gtp_xact, 0,
+                        OGS_GTP2_DELETE_SESSION_RESPONSE_TYPE,
+                        OGS_GTP2_CAUSE_CONTEXT_NOT_FOUND);
+                break;
+            }
+            e->sess = sess;
+            ogs_fsm_dispatch(&sess->sm, e);
             break;
         case OGS_GTP2_MODIFY_BEARER_REQUEST_TYPE:
             smf_s5c_handle_modify_bearer_request(
@@ -161,8 +168,12 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
                 sess, gtp_xact, &gtp2_message.update_bearer_response);
             break;
         case OGS_GTP2_DELETE_BEARER_RESPONSE_TYPE:
-            smf_s5c_handle_delete_bearer_response(
-                sess, gtp_xact, &gtp2_message.delete_bearer_response);
+            if (!sess) {
+                /* TODO: NACK the message */
+                break;
+            }
+            e->sess = sess;
+            ogs_fsm_dispatch(&sess->sm, e);
             break;
         case OGS_GTP2_BEARER_RESOURCE_COMMAND_TYPE:
             smf_s5c_handle_bearer_resource_command(
@@ -230,8 +241,14 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
             ogs_fsm_dispatch(&sess->sm, e);
             break;
         case OGS_GTP1_DELETE_PDP_CONTEXT_REQUEST_TYPE:
-            smf_gn_handle_delete_pdp_context_request(
-                sess, gtp_xact, &gtp1_message.delete_pdp_context_request);
+            if (!sess) {
+                ogs_gtp1_send_error_message(gtp_xact, 0,
+                        OGS_GTP1_DELETE_PDP_CONTEXT_RESPONSE_TYPE,
+                        OGS_GTP1_CAUSE_NON_EXISTENT);
+                break;
+            }
+            e->sess = sess;
+            ogs_fsm_dispatch(&sess->sm, e);
             break;
         case OGS_GTP1_UPDATE_PDP_CONTEXT_REQUEST_TYPE:
             smf_gn_handle_update_pdp_context_request(
@@ -258,16 +275,12 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
 
         switch(gx_message->cmd_code) {
         case OGS_DIAM_GX_CMD_CODE_CREDIT_CONTROL:
-            gtp_xact = e->gtp_xact;
-            ogs_assert(gtp_xact);
-
             switch(gx_message->cc_request_type) {
             case OGS_DIAM_GX_CC_REQUEST_TYPE_INITIAL_REQUEST:
                 ogs_fsm_dispatch(&sess->sm, e);
                 break;
             case OGS_DIAM_GX_CC_REQUEST_TYPE_TERMINATION_REQUEST:
-                smf_gx_handle_cca_termination_request(
-                        sess, gx_message, gtp_xact);
+                ogs_fsm_dispatch(&sess->sm, e);
                 break;
             default:
                 ogs_error("Not implemented(%d)", gx_message->cc_request_type);
@@ -302,14 +315,12 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
                 ogs_fsm_dispatch(&sess->sm, e);
                 break;
             case OGS_DIAM_GY_CC_REQUEST_TYPE_UPDATE_REQUEST:
-                    ogs_assert(e->pfcp_xact);
-                    smf_gy_handle_cca_update_request(
-                            sess, gy_message, e->pfcp_xact);
+                ogs_assert(e->pfcp_xact);
+                smf_gy_handle_cca_update_request(
+                        sess, gy_message, e->pfcp_xact);
             break;
             case OGS_DIAM_GY_CC_REQUEST_TYPE_TERMINATION_REQUEST:
-                ogs_assert(e->gtp_xact);
-                smf_gy_handle_cca_termination_request(
-                        sess, gy_message, e->gtp_xact);
+                ogs_fsm_dispatch(&sess->sm, e);
                 break;
             default:
                 ogs_error("Not implemented(%d)", gy_message->cc_request_type);
@@ -328,6 +339,25 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
         ogs_free(gy_message);
         break;
 
+    case SMF_EVT_S6B_MESSAGE:
+        ogs_assert(e);
+        s6b_message = e->s6b_message;
+        ogs_assert(s6b_message);
+        sess = e->sess;
+        ogs_assert(sess);
+
+        switch(s6b_message->cmd_code) {
+        case OGS_DIAM_S6B_CMD_SESSION_TERMINATION:
+            ogs_fsm_dispatch(&sess->sm, e);
+            break;
+        default:
+            ogs_error("Invalid type(%d)", s6b_message->cmd_code);
+            break;
+        }
+
+        ogs_free(s6b_message);
+        break;
+
     case SMF_EVT_N4_MESSAGE:
         ogs_assert(e);
         recvbuf = e->pkbuf;
@@ -716,9 +746,6 @@ void smf_state_operational(ogs_fsm_t *s, smf_event_t *e)
             if (OGS_FSM_CHECK(&sess->sm, smf_gsm_state_exception)) {
                 ogs_error("[%s] State machine exception", smf_ue->supi);
                 SMF_SESS_CLEAR(sess);
-            } else if (OGS_FSM_CHECK(
-                        &sess->sm, smf_gsm_state_session_will_release)) {
-                SMF_SESS_CLEAR(sess);
             }
             break;
 
diff --git a/src/smf/smf-sm.h b/src/smf/smf-sm.h
index 72960fe4a..a580bd9c7 100644
--- a/src/smf/smf-sm.h
+++ b/src/smf/smf-sm.h
@@ -43,13 +43,15 @@ void smf_nf_state_exception(ogs_fsm_t *s, smf_event_t *e);
 
 void smf_gsm_state_initial(ogs_fsm_t *s, smf_event_t *e);
 void smf_gsm_state_final(ogs_fsm_t *s, smf_event_t *e);
+void smf_gsm_state_initial_wait_auth(ogs_fsm_t *s, smf_event_t *e);
+void smf_gsm_state_initial_wait_pfcp_establishment(ogs_fsm_t *s, smf_event_t *e);
 void smf_gsm_state_operational(ogs_fsm_t *s, smf_event_t *e);
+void smf_gsm_state_release_wait_pfcp_deletion(ogs_fsm_t *s, smf_event_t *e);
+void smf_gsm_state_release_wait_auth(ogs_fsm_t *s, smf_event_t *e);
 void smf_gsm_state_session_will_release(ogs_fsm_t *s, smf_event_t *e);
 void smf_gsm_state_exception(ogs_fsm_t *s, smf_event_t *e);
 
 void smf_pfcp_state_initial(ogs_fsm_t *s, smf_event_t *e);
-void smf_gsm_state_initial_wait_auth(ogs_fsm_t *s, smf_event_t *e);
-void smf_gsm_state_initial_wait_pfcp_establishment(ogs_fsm_t *s, smf_event_t *e);
 void smf_pfcp_state_final(ogs_fsm_t *s, smf_event_t *e);
 void smf_pfcp_state_will_associate(ogs_fsm_t *s, smf_event_t *e);
 void smf_pfcp_state_associated(ogs_fsm_t *s, smf_event_t *e);