diff --git a/configs/open5gs/mme.yaml.in b/configs/open5gs/mme.yaml.in
index 722648dd6..871c7006c 100644
--- a/configs/open5gs/mme.yaml.in
+++ b/configs/open5gs/mme.yaml.in
@@ -437,5 +437,4 @@ usrsctp:
 #      value: 3240 # 54 minutes * 60 = 3240 seconds
 #    t3423:
 #      value: 720  # 12 minutes * 60 = 720 seconds
-#
 time:
diff --git a/src/mme/emm-sm.c b/src/mme/emm-sm.c
index 570069818..8fcb552c2 100644
--- a/src/mme/emm-sm.c
+++ b/src/mme/emm-sm.c
@@ -61,6 +61,8 @@ void emm_state_de_registered(ogs_fsm_t *s, mme_event_t *e)
 
     ogs_assert(e);
 
+    mme_sm_debug(e);
+
     mme_ue = e->mme_ue;
     ogs_assert(mme_ue);
 
@@ -110,6 +112,8 @@ void emm_state_registered(ogs_fsm_t *s, mme_event_t *e)
 
     ogs_assert(e);
 
+    mme_sm_debug(e);
+
     mme_ue = e->mme_ue;
     ogs_assert(mme_ue);
 
@@ -176,6 +180,37 @@ void emm_state_registered(ogs_fsm_t *s, mme_event_t *e)
             }
             break;
 
+        case MME_TIMER_MOBILE_REACHABLE:
+            ogs_info("[%s] Mobile Reachable timer expired", mme_ue->imsi_bcd);
+            CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
+            /* TS 24.301 5.3.5
+             * Upon expiry of the mobile reachable timer the network shall
+             * start the implicit detach timer.
+             */
+            ogs_debug("[%s] Starting Implicit Detach timer",
+                mme_ue->imsi_bcd);
+            ogs_timer_start(mme_ue->t_implicit_detach.timer,
+                ogs_time_from_sec(mme_self()->time.t3412.value + 240));
+            break;
+
+        case MME_TIMER_IMPLICIT_DETACH:
+            ogs_info("[%s] Implicit Detach timer expired, detaching UE",
+                mme_ue->imsi_bcd);
+            CLEAR_MME_UE_TIMER(mme_ue->t_implicit_detach);
+            /* TS 24.301 5.3.5
+             * If the implicit detach timer expires before the UE contacts
+             * the network, the network shall implicitly detach the UE.
+             */
+            mme_ue->detach_type = MME_DETACH_TYPE_MME_IMPLICIT;
+            if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
+                ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
+            } else {
+                mme_send_delete_session_or_detach(mme_ue);
+            }
+
+            OGS_FSM_TRAN(s, &emm_state_de_registered);
+            break;
+
         default:
             ogs_error("Unknown timer[%s:%d]",
                     mme_timer_get_name(e->timer_id), e->timer_id);
@@ -195,9 +230,11 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e)
     enb_ue_t *enb_ue = NULL;
     ogs_nas_eps_message_t *message = NULL;
     ogs_nas_security_header_type_t h;
-    
+
     ogs_assert(e);
-        
+
+    mme_sm_debug(e);
+
     mme_ue = e->mme_ue;
     ogs_assert(mme_ue);
 
@@ -640,6 +677,24 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e)
                 break;
             }
 
+            if (!MME_UE_HAVE_IMSI(mme_ue)) {
+                ogs_warn("Detach request : Unknown UE");
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (!SECURITY_CONTEXT_IS_VALID(mme_ue)) {
+                ogs_warn("No Security Context : IMSI[%s]", mme_ue->imsi_bcd);
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
             if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
                 ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
             } else {
diff --git a/src/mme/mme-context.c b/src/mme/mme-context.c
index 35d07721a..ac85054b6 100644
--- a/src/mme/mme-context.c
+++ b/src/mme/mme-context.c
@@ -2402,6 +2402,22 @@ mme_ue_t *mme_ue_add(enb_ue_t *enb_ue)
         return NULL;
     }
     mme_ue->t3470.pkbuf = NULL;
+    mme_ue->t_mobile_reachable.timer = ogs_timer_add(
+            ogs_app()->timer_mgr, mme_timer_mobile_reachable_expire, mme_ue);
+    if (!mme_ue->t_mobile_reachable.timer) {
+        ogs_error("ogs_timer_add() failed");
+        ogs_pool_free(&mme_ue_pool, mme_ue);
+        return NULL;
+    }
+    mme_ue->t_mobile_reachable.pkbuf = NULL;
+    mme_ue->t_implicit_detach.timer = ogs_timer_add(
+            ogs_app()->timer_mgr, mme_timer_implicit_detach_expire, mme_ue);
+    if (!mme_ue->t_implicit_detach.timer) {
+        ogs_error("ogs_timer_add() failed");
+        ogs_pool_free(&mme_ue_pool, mme_ue);
+        return NULL;
+    }
+    mme_ue->t_implicit_detach.pkbuf = NULL;
 
     mme_ebi_pool_init(mme_ue);
 
@@ -2493,6 +2509,8 @@ void mme_ue_remove(mme_ue_t *mme_ue)
     ogs_timer_delete(mme_ue->t3450.timer);
     ogs_timer_delete(mme_ue->t3460.timer);
     ogs_timer_delete(mme_ue->t3470.timer);
+    ogs_timer_delete(mme_ue->t_mobile_reachable.timer);
+    ogs_timer_delete(mme_ue->t_implicit_detach.timer);
 
     enb_ue_unlink(mme_ue);
 
diff --git a/src/mme/mme-context.h b/src/mme/mme-context.h
index 8e98e8413..182c5bbfe 100644
--- a/src/mme/mme-context.h
+++ b/src/mme/mme-context.h
@@ -517,6 +517,8 @@ struct mme_ue_s {
         CLEAR_MME_UE_TIMER((__mME)->t3450); \
         CLEAR_MME_UE_TIMER((__mME)->t3460); \
         CLEAR_MME_UE_TIMER((__mME)->t3470); \
+        CLEAR_MME_UE_TIMER((__mME)->t_mobile_reachable); \
+        CLEAR_MME_UE_TIMER((__mME)->t_implicit_detach); \
         \
         ogs_list_for_each(&mme_ue->sess_list, sess) { \
             ogs_list_for_each(&sess->bearer_list, bearer) { \
@@ -537,7 +539,8 @@ struct mme_ue_s {
         ogs_pkbuf_t     *pkbuf;
         ogs_timer_t     *timer;
         uint32_t        retry_count;;
-    } t3413, t3422, t3450, t3460, t3470;
+    } t3413, t3422, t3450, t3460, t3470, t_mobile_reachable, 
+        t_implicit_detach;
 
 #define CLEAR_SERVICE_INDICATOR(__mME) \
     do { \
diff --git a/src/mme/mme-path.c b/src/mme/mme-path.c
index eb765ad60..d94295151 100644
--- a/src/mme/mme-path.c
+++ b/src/mme/mme-path.c
@@ -22,6 +22,7 @@
 #include "sgsap-path.h"
 #include "mme-gtp-path.h"
 #include "mme-path.h"
+#include "mme-fd-path.h"
 #include "mme-sm.h"
 
 void mme_send_delete_session_or_detach(mme_ue_t *mme_ue)
@@ -61,10 +62,31 @@ void mme_send_delete_session_or_detach(mme_ue_t *mme_ue)
         }
         break;
 
-    /* MME Implicit Detach, ie: Lost Communication */
+    /* MME Implicit Detach, ie: Lost Communication
+     * TS23.401 - V16.10.0
+     * Ch 5.3.8.3 MME-initiated Detach procedure (Without Step 1)
+     */
     case MME_DETACH_TYPE_MME_IMPLICIT:
-        ogs_fatal("Not Implemented : MME_DETACH_TYPE_MME_IMPLICIT");
-        ogs_assert_if_reached();
+        ogs_debug("Implicit MME Detach");
+        if (SESSION_CONTEXT_IS_AVAILABLE(mme_ue)) {
+            mme_gtp_send_delete_all_sessions(mme_ue,
+                OGS_GTP_DELETE_SEND_RELEASE_WITH_UE_CONTEXT_REMOVE);
+        } else {
+            enb_ue_t *enb_ue = enb_ue_cycle(mme_ue->enb_ue);
+            if (enb_ue) {
+                ogs_assert(OGS_OK ==
+                    s1ap_send_ue_context_release_command(enb_ue,
+                        S1AP_Cause_PR_nas, S1AP_CauseNas_normal_release,
+                        S1AP_UE_CTX_REL_UE_CONTEXT_REMOVE, 0));
+            } else {
+                if (mme_ue->location_updated_but_not_canceled_yet == true) {
+                    mme_s6a_send_pur(mme_ue);
+                } else {
+                    mme_ue_hash_remove(mme_ue);
+                    mme_ue_remove(mme_ue);
+                }
+            }
+        }
         break;
 
     /* HSS Implicit Detach, ie: MME-UPDATE-PROCEDURE
diff --git a/src/mme/mme-s11-handler.c b/src/mme/mme-s11-handler.c
index eacbf1c9a..5879a699b 100644
--- a/src/mme/mme-s11-handler.c
+++ b/src/mme/mme-s11-handler.c
@@ -904,11 +904,27 @@ void mme_s11_handle_create_bearer_request(
 
     if (OGS_FSM_CHECK(&default_bearer->sm, esm_state_active)) {
         if (ECM_IDLE(mme_ue)) {
-            MME_STORE_PAGING_INFO(mme_ue,
+            if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+                /*
+                * TS 24.301 5.3.7
+                * If ISR is not activated, the network behaviour upon expiry of
+                * the mobile reachable timer is network dependent, but typically
+                * the network stops sending paging messages to the UE on the
+                * first expiry, and may take other appropriate actions
+                */
+                ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                    mme_ue->imsi_bcd);
+
+                ogs_assert(OGS_OK ==
+                    mme_gtp_send_create_bearer_response(
+                        bearer, OGS_GTP2_CAUSE_UNABLE_TO_PAGE_UE));
+            } else {
+                MME_STORE_PAGING_INFO(mme_ue,
                     MME_PAGING_TYPE_CREATE_BEARER, bearer);
-            r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-            ogs_expect(r == OGS_OK);
-            ogs_assert(r != OGS_ERROR);
+                r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+                ogs_expect(r == OGS_OK);
+                ogs_assert(r != OGS_ERROR);
+            }
         } else {
             r = nas_eps_send_activate_dedicated_bearer_context_request(bearer);
             ogs_expect(r == OGS_OK);
@@ -1036,11 +1052,27 @@ void mme_s11_handle_update_bearer_request(
     if (req->bearer_contexts.bearer_level_qos.presence == 1 ||
         req->bearer_contexts.tft.presence == 1) {
         if (ECM_IDLE(mme_ue)) {
-            MME_STORE_PAGING_INFO(mme_ue,
+            if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+                /*
+                * TS 24.301 5.3.7
+                * If ISR is not activated, the network behaviour upon expiry of
+                * the mobile reachable timer is network dependent, but typically
+                * the network stops sending paging messages to the UE on the
+                * first expiry, and may take other appropriate actions
+                */
+                ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                    mme_ue->imsi_bcd);
+
+                ogs_assert(OGS_OK ==
+                    mme_gtp_send_update_bearer_response(
+                        bearer, OGS_GTP2_CAUSE_UNABLE_TO_PAGE_UE));
+            } else {
+                MME_STORE_PAGING_INFO(mme_ue,
                     MME_PAGING_TYPE_UPDATE_BEARER, bearer);
-            r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-            ogs_expect(r == OGS_OK);
-            ogs_assert(r != OGS_ERROR);
+                r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+                ogs_expect(r == OGS_OK);
+                ogs_assert(r != OGS_ERROR);
+            }
         } else {
             r = nas_eps_send_modify_bearer_context_request(bearer,
                     req->bearer_contexts.bearer_level_qos.presence,
@@ -1175,10 +1207,27 @@ void mme_s11_handle_delete_bearer_request(
     bearer->delete.xact = xact;
 
     if (ECM_IDLE(mme_ue)) {
-        MME_STORE_PAGING_INFO(mme_ue, MME_PAGING_TYPE_DELETE_BEARER, bearer);
-        r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-        ogs_expect(r == OGS_OK);
-        ogs_assert(r != OGS_ERROR);
+        if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+            /*
+            * TS 24.301 5.3.7
+            * If ISR is not activated, the network behaviour upon expiry of
+            * the mobile reachable timer is network dependent, but typically
+            * the network stops sending paging messages to the UE on the
+            * first expiry, and may take other appropriate actions
+            */
+            ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                mme_ue->imsi_bcd);
+
+            ogs_assert(OGS_OK ==
+                mme_gtp_send_delete_bearer_response(
+                    bearer, OGS_GTP2_CAUSE_UNABLE_TO_PAGE_UE));
+        } else {
+            MME_STORE_PAGING_INFO(mme_ue,
+                MME_PAGING_TYPE_DELETE_BEARER, bearer);
+            r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+            ogs_expect(r == OGS_OK);
+            ogs_assert(r != OGS_ERROR);
+        }
     } else {
         r = nas_eps_send_deactivate_bearer_context_request(bearer);
         ogs_expect(r == OGS_OK);
@@ -1435,12 +1484,26 @@ void mme_s11_handle_downlink_data_notification(
  * before step 9, the MME shall not send S1 interface paging messages
  */
     if (ECM_IDLE(mme_ue)) {
-        MME_STORE_PAGING_INFO(mme_ue,
+        if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+            /*
+            * TS 24.301 5.3.7
+            * If ISR is not activated, the network behaviour upon expiry of
+            * the mobile reachable timer is network dependent, but typically
+            * the network stops sending paging messages to the UE on the
+            * first expiry, and may take other appropriate actions
+            */
+            ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                mme_ue->imsi_bcd);
+            ogs_assert(OGS_OK ==
+                mme_gtp_send_downlink_data_notification_ack(
+                    bearer, OGS_GTP2_CAUSE_UNABLE_TO_PAGE_UE));
+        } else {
+            MME_STORE_PAGING_INFO(mme_ue,
                 MME_PAGING_TYPE_DOWNLINK_DATA_NOTIFICATION, bearer);
-        r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-        ogs_expect(r == OGS_OK);
-        ogs_assert(r != OGS_ERROR);
-
+            r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+            ogs_expect(r == OGS_OK);
+            ogs_assert(r != OGS_ERROR);
+        }
     } else if (ECM_CONNECTED(mme_ue)) {
         if (cause_value == OGS_GTP2_CAUSE_ERROR_INDICATION_RECEIVED) {
 
diff --git a/src/mme/mme-s6a-handler.c b/src/mme/mme-s6a-handler.c
index 155bf58cd..4f298f8bd 100644
--- a/src/mme/mme-s6a-handler.c
+++ b/src/mme/mme-s6a-handler.c
@@ -264,10 +264,28 @@ void mme_s6a_handle_clr(mme_ue_t *mme_ue, ogs_diam_s6a_message_t *s6a_message)
          * we need to check whether UE is IDLE or not.
          */
         if (ECM_IDLE(mme_ue)) {
-            MME_STORE_PAGING_INFO(mme_ue, MME_PAGING_TYPE_DETACH_TO_UE, NULL);
-            r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-            ogs_expect(r == OGS_OK);
-            ogs_assert(r != OGS_ERROR);
+            if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+                /*
+                * TS 24.301 5.3.7
+                * If ISR is not activated, the network behaviour upon expiry of
+                * the mobile reachable timer is network dependent, but typically
+                * the network stops sending paging messages to the UE on the
+                * first expiry, and may take other appropriate actions
+                */
+                ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                    mme_ue->imsi_bcd);
+                if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
+                    ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
+                } else {
+                    mme_send_delete_session_or_detach(mme_ue);
+                }
+            } else {
+                MME_STORE_PAGING_INFO(mme_ue,
+                    MME_PAGING_TYPE_DETACH_TO_UE, NULL);
+                r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+                ogs_expect(r == OGS_OK);
+                ogs_assert(r != OGS_ERROR);
+            }
         } else {
             r = nas_eps_send_detach_request(mme_ue);
             ogs_expect(r == OGS_OK);
diff --git a/src/mme/mme-sm.c b/src/mme/mme-sm.c
index ee4dcfc20..34596d6de 100644
--- a/src/mme/mme-sm.c
+++ b/src/mme/mme-sm.c
@@ -307,6 +307,9 @@ void mme_state_operational(ogs_fsm_t *s, mme_event_t *e)
                 ogs_assert(r != OGS_ERROR);
             }
             enb_ue_associate_mme_ue(enb_ue, mme_ue);
+            ogs_debug("Mobile Reachable timer stopped for IMSI[%s]", 
+                mme_ue->imsi_bcd);
+            CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
         }
 
         ogs_assert(mme_ue);
diff --git a/src/mme/mme-timer.c b/src/mme/mme-timer.c
index 1e3780e60..f2b6204f7 100644
--- a/src/mme/mme-timer.c
+++ b/src/mme/mme-timer.c
@@ -92,6 +92,10 @@ const char *mme_timer_get_name(mme_timer_e id)
         return "MME_TIMER_T3470";
     case MME_TIMER_T3489:
         return "MME_TIMER_T3489";
+    case MME_TIMER_MOBILE_REACHABLE:
+        return "MME_TIMER_MOBILE_REACHABLE";
+    case MME_TIMER_IMPLICIT_DETACH:
+        return "MME_TIMER_IMPLICIT_DETACH";
     case MME_TIMER_SGS_CLI_CONN_TO_SRV:
         return "MME_TIMER_SGS_CLI_CONN_TO_SRV";
     case MME_TIMER_S1_HOLDING:
@@ -160,6 +164,14 @@ void mme_timer_t3470_expire(void *data)
 {
     emm_timer_event_send(MME_TIMER_T3470, data);
 }
+void mme_timer_mobile_reachable_expire(void *data)
+{
+    emm_timer_event_send(MME_TIMER_MOBILE_REACHABLE, data);
+}
+void mme_timer_implicit_detach_expire(void *data)
+{
+    emm_timer_event_send(MME_TIMER_IMPLICIT_DETACH, data);
+}
 
 static void esm_timer_event_send(
         mme_timer_e timer_id, mme_bearer_t *bearer)
diff --git a/src/mme/mme-timer.h b/src/mme/mme-timer.h
index 8356311f6..f7cdf415c 100644
--- a/src/mme/mme-timer.h
+++ b/src/mme/mme-timer.h
@@ -40,6 +40,9 @@ typedef enum {
     MME_TIMER_T3470,
     MME_TIMER_T3489,
 
+    MME_TIMER_MOBILE_REACHABLE,
+    MME_TIMER_IMPLICIT_DETACH,
+
     MME_TIMER_S11_HOLDING,
 
     MME_TIMER_SGS_CLI_CONN_TO_SRV,
@@ -67,6 +70,9 @@ void mme_timer_t3460_expire(void *data);
 void mme_timer_t3470_expire(void *data);
 void mme_timer_t3489_expire(void *data);
 
+void mme_timer_mobile_reachable_expire(void *data);
+void mme_timer_implicit_detach_expire(void *data);
+
 void mme_timer_sgs_cli_conn_to_srv(void *data);
 void mme_timer_s1_holding_timer_expire(void *data);
 void mme_timer_s11_holding_timer_expire(void *data);
diff --git a/src/mme/s1ap-handler.c b/src/mme/s1ap-handler.c
index 1d0520500..b7024b850 100644
--- a/src/mme/s1ap-handler.c
+++ b/src/mme/s1ap-handler.c
@@ -330,6 +330,9 @@ void s1ap_handle_initial_ue_message(mme_enb_t *enb, ogs_s1ap_message_t *message)
                     ogs_assert(r != OGS_ERROR);
                 }
                 enb_ue_associate_mme_ue(enb_ue, mme_ue);
+                ogs_debug("Mobile Reachable timer stopped for IMSI[%s]", 
+                    mme_ue->imsi_bcd);
+                CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
             }
         }
     }
@@ -1535,6 +1538,13 @@ void s1ap_handle_ue_context_release_action(enb_ue_t *enb_ue)
          * to prevent retransmission of NAS messages.
          */
         CLEAR_MME_UE_ALL_TIMERS(mme_ue);
+
+        if (OGS_FSM_CHECK(&mme_ue->sm, emm_state_registered)) {
+            ogs_debug("Mobile Reachable timer started for IMSI[%s]",
+                mme_ue->imsi_bcd);
+            ogs_timer_start(mme_ue->t_mobile_reachable.timer,
+                ogs_time_from_sec(mme_self()->time.t3412.value + 240));
+        }
     }
 
     switch (enb_ue->ue_ctx_rel_action) {
@@ -3099,6 +3109,8 @@ void s1ap_handle_handover_notification(
             target_ue->enb_ue_s1ap_id, target_ue->mme_ue_s1ap_id);
 
     enb_ue_associate_mme_ue(target_ue, mme_ue);
+    ogs_debug("Mobile Reachable timer stopped for IMSI[%s]", mme_ue->imsi_bcd);
+    CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
 
     memcpy(&target_ue->saved.tai.plmn_id, pLMNidentity->buf,
             sizeof(target_ue->saved.tai.plmn_id));
diff --git a/src/mme/s1ap-path.c b/src/mme/s1ap-path.c
index 766ca067c..59fe0f1f3 100644
--- a/src/mme/s1ap-path.c
+++ b/src/mme/s1ap-path.c
@@ -380,6 +380,8 @@ int s1ap_send_paging(mme_ue_t *mme_ue, S1AP_CNDomain_t cn_domain)
     int i;
     int rv;
 
+    ogs_assert(ogs_timer_running(mme_ue->t_implicit_detach.timer) == false);
+
     /* Find enB with matched TAI */
     ogs_list_for_each(&mme_self()->enb_list, enb) {
         for (i = 0; i < enb->num_of_supported_ta_list; i++) {
diff --git a/src/mme/sgsap-handler.c b/src/mme/sgsap-handler.c
index 0bf60357a..2032ed6af 100644
--- a/src/mme/sgsap-handler.c
+++ b/src/mme/sgsap-handler.c
@@ -387,20 +387,53 @@ void sgsap_handle_paging_request(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
 
         if (ECM_IDLE(mme_ue)) {
             if (CS_CALL_SERVICE_INDICATOR(mme_ue)) {
-                /* UE will respond Extended Service Request in PS CNDomain*/
-                MME_STORE_PAGING_INFO(mme_ue,
-                        MME_PAGING_TYPE_CS_CALL_SERVICE, NULL);
-                r = s1ap_send_paging(mme_ue, S1AP_CNDomain_cs);
-                ogs_expect(r == OGS_OK);
-                ogs_assert(r != OGS_ERROR);
+                if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+                    /*
+                    * TS 24.301 5.3.7
+                    * If ISR is not activated, the network behaviour upon
+                    * expiry of the mobile reachable timer is network dependent,
+                    * but typically the network stops sending paging messages to
+                    * the UE on the first expiry, and may take other appropriate
+                    * actions
+                    */
+                    ogs_debug("[%s] Paging stopped: Mobile Reachable timeout",
+                        mme_ue->imsi_bcd);
 
+                    ogs_assert(OGS_OK ==
+                        sgsap_send_paging_reject(
+                            mme_ue, SGSAP_SGS_CAUSE_UE_UNREACHABLE));
+                } else {
+                    /* UE will respond Extended Service Request in PS CNDomain*/
+                    MME_STORE_PAGING_INFO(mme_ue,
+                        MME_PAGING_TYPE_CS_CALL_SERVICE, NULL);
+                    r = s1ap_send_paging(mme_ue, S1AP_CNDomain_cs);
+                    ogs_expect(r == OGS_OK);
+                    ogs_assert(r != OGS_ERROR);
+                }
             } else if (SMS_SERVICE_INDICATOR(mme_ue)) {
-                /* UE will respond Service Request in PS CNDomain*/
-                MME_STORE_PAGING_INFO(mme_ue,
+                if (ogs_timer_running(mme_ue->t_implicit_detach.timer)) {
+                    /*
+                    * TS 24.301 5.3.7
+                    * If ISR is not activated, the network behaviour upon
+                    * expiry of the mobile reachable timer is network dependent,
+                    * but typically the network stops sending paging messages to
+                    * the UE on the first expiry, and may take other appropriate
+                    * actions
+                    */
+                    ogs_debug("[%s] Paging stopped: Mobile Reachable timer expiry",
+                        mme_ue->imsi_bcd);
+
+                    ogs_assert(OGS_OK ==
+                        sgsap_send_paging_reject(
+                            mme_ue, SGSAP_SGS_CAUSE_UE_UNREACHABLE));
+                } else {
+                    /* UE will respond Service Request in PS CNDomain*/
+                    MME_STORE_PAGING_INFO(mme_ue,
                         MME_PAGING_TYPE_SMS_SERVICE, NULL);
-                r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
-                ogs_expect(r == OGS_OK);
-                ogs_assert(r != OGS_ERROR);
+                    r = s1ap_send_paging(mme_ue, S1AP_CNDomain_ps);
+                    ogs_expect(r == OGS_OK);
+                    ogs_assert(r != OGS_ERROR);
+                }
             } else
                 goto paging_reject;