diff --git a/src/mme/sgsap-build.c b/src/mme/sgsap-build.c
index 18317f582..d27b4a44d 100644
--- a/src/mme/sgsap-build.c
+++ b/src/mme/sgsap-build.c
@@ -91,6 +91,7 @@ ogs_pkbuf_t *sgsap_build_location_update_request(mme_ue_t *mme_ue)
 
     return pkbuf;
 }
+
 ogs_pkbuf_t *sgsap_build_tmsi_reallocation_complete(mme_ue_t *mme_ue)
 {
     mme_csmap_t *csmap = NULL;
@@ -124,6 +125,96 @@ ogs_pkbuf_t *sgsap_build_tmsi_reallocation_complete(mme_ue_t *mme_ue)
     return pkbuf;
 }
 
+ogs_pkbuf_t *sgsap_build_ue_activity_indication(mme_ue_t *mme_ue)
+{
+    ogs_tlv_t *root = NULL;
+    ogs_pkbuf_t *pkbuf = NULL;
+
+    ogs_assert(mme_ue);
+
+    root = ogs_tlv_add(NULL, OGS_TLV_MODE_T1_L1, SGSAP_IE_IMSI_TYPE,
+            SGSAP_IE_IMSI_LEN, 0, &mme_ue->nas_mobile_identity_imsi);
+
+    /* TODO: Maximum UE Availability Time */
+
+    pkbuf = ogs_pkbuf_alloc(NULL, OGS_MAX_SDU_LEN);
+    if (!pkbuf) {
+        ogs_error("ogs_pkbuf_alloc() failed");
+        ogs_tlv_free_all(root);
+        return NULL;
+    }
+    ogs_pkbuf_put_u8(pkbuf, SGSAP_UE_ACTIVITY_INDICATION);
+    ogs_pkbuf_put(pkbuf, OGS_MAX_SDU_LEN-1);
+
+    ogs_pkbuf_trim(pkbuf, 1+ogs_tlv_render(root,
+            pkbuf->data+1, OGS_MAX_SDU_LEN-1));
+
+    ogs_tlv_free_all(root);
+
+    return pkbuf;
+}
+
+ogs_pkbuf_t *sgsap_build_alert_ack(mme_ue_t *mme_ue)
+{
+    ogs_tlv_t *root = NULL;
+    ogs_pkbuf_t *pkbuf = NULL;
+
+    ogs_assert(mme_ue);
+
+    root = ogs_tlv_add(NULL, OGS_TLV_MODE_T1_L1, SGSAP_IE_IMSI_TYPE,
+            SGSAP_IE_IMSI_LEN, 0, &mme_ue->nas_mobile_identity_imsi);
+
+    pkbuf = ogs_pkbuf_alloc(NULL, OGS_MAX_SDU_LEN);
+    if (!pkbuf) {
+        ogs_error("ogs_pkbuf_alloc() failed");
+        ogs_tlv_free_all(root);
+        return NULL;
+    }
+    ogs_pkbuf_put_u8(pkbuf, SGSAP_ALERT_ACK);
+    ogs_pkbuf_put(pkbuf, OGS_MAX_SDU_LEN-1);
+
+    ogs_pkbuf_trim(pkbuf, 1+ogs_tlv_render(root,
+            pkbuf->data+1, OGS_MAX_SDU_LEN-1));
+
+    ogs_tlv_free_all(root);
+
+    return pkbuf;
+}
+
+ogs_pkbuf_t *sgsap_build_alert_reject(
+    ogs_nas_mobile_identity_imsi_t *nas_mobile_identity_imsi,
+    int nas_mobile_identity_imsi_len, uint8_t sgs_cause)
+{
+    ogs_tlv_t *root = NULL;
+    ogs_pkbuf_t *pkbuf = NULL;
+
+    ogs_assert(nas_mobile_identity_imsi);
+    ogs_assert(nas_mobile_identity_imsi_len == SGSAP_IE_IMSI_LEN);
+
+    root = ogs_tlv_add(NULL, OGS_TLV_MODE_T1_L1,
+            SGSAP_IE_IMSI_TYPE, SGSAP_IE_IMSI_LEN, 0, nas_mobile_identity_imsi);
+    ogs_tlv_add(root, OGS_TLV_MODE_T1_L1,
+            SGSAP_IE_SGS_CAUSE_TYPE, SGSAP_IE_SGS_CAUSE_LEN, 0, &sgs_cause);
+
+    ogs_debug("    CAUSE[%d]", sgs_cause);
+
+    pkbuf = ogs_pkbuf_alloc(NULL, OGS_MAX_SDU_LEN);
+    if (!pkbuf) {
+        ogs_error("ogs_pkbuf_alloc() failed");
+        ogs_tlv_free_all(root);
+        return NULL;
+    }
+    ogs_pkbuf_put_u8(pkbuf, SGSAP_ALERT_REJECT);
+    ogs_pkbuf_put(pkbuf, OGS_MAX_SDU_LEN-1);
+
+    ogs_pkbuf_trim(pkbuf, 1+ogs_tlv_render(root,
+            pkbuf->data+1, OGS_MAX_SDU_LEN-1));
+
+    ogs_tlv_free_all(root);
+
+    return pkbuf;
+}
+
 ogs_pkbuf_t *sgsap_build_detach_indication(mme_ue_t *mme_ue)
 {
     mme_csmap_t *csmap = NULL;
diff --git a/src/mme/sgsap-build.h b/src/mme/sgsap-build.h
index 12810e9c8..2364d10c8 100644
--- a/src/mme/sgsap-build.h
+++ b/src/mme/sgsap-build.h
@@ -30,6 +30,11 @@ extern "C" {
 
 ogs_pkbuf_t *sgsap_build_location_update_request(mme_ue_t *mme_ue);
 ogs_pkbuf_t *sgsap_build_tmsi_reallocation_complete(mme_ue_t *mme_ue);
+ogs_pkbuf_t *sgsap_build_ue_activity_indication(mme_ue_t *mme_ue);
+ogs_pkbuf_t *sgsap_build_alert_ack(mme_ue_t *mme_ue);
+ogs_pkbuf_t *sgsap_build_alert_reject(
+    ogs_nas_mobile_identity_imsi_t *nas_mobile_identity_imsi,
+    int nas_mobile_identity_imsi_len, uint8_t sgs_cause);
 ogs_pkbuf_t *sgsap_build_detach_indication(mme_ue_t *mme_ue);
 ogs_pkbuf_t *sgsap_build_mo_csfb_indication(mme_ue_t *mme_ue);
 ogs_pkbuf_t *sgsap_build_paging_reject(
diff --git a/src/mme/sgsap-handler.c b/src/mme/sgsap-handler.c
index 62c82f4c2..a30e681a7 100644
--- a/src/mme/sgsap-handler.c
+++ b/src/mme/sgsap-handler.c
@@ -405,6 +405,98 @@ error:
     return;
 }
 
+void sgsap_handle_alert_request(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
+{
+    ogs_tlv_t *root = NULL, *iter = NULL;
+    mme_ue_t *mme_ue = NULL;
+    uint8_t sgs_cause = SGSAP_SGS_CAUSE_IMSI_UNKNOWN;
+
+    char imsi_bcd[OGS_MAX_IMSI_BCD_LEN+1] = {0, };
+
+    ogs_nas_mobile_identity_imsi_t *nas_mobile_identity_imsi = NULL;
+    int nas_mobile_identity_imsi_len = 0;
+
+    ogs_assert(vlr);
+    ogs_assert(pkbuf);
+
+    ogs_warn("[SGSAP] Rx ALERT-REQUEST");
+
+    ogs_pkbuf_pull(pkbuf, 1);
+
+    root = ogs_tlv_parse_block(pkbuf->len, pkbuf->data, OGS_TLV_MODE_T1_L1);
+    if (!root) {
+        ogs_error("ogs_tlv_parse_block() failed");
+        sgs_cause = SGSAP_SGS_CAUSE_SEMANTICALLY_INCORRECT_MESSAGE;
+        goto alert_reject;
+    }
+
+    iter = root;
+    while (iter) {
+        switch (iter->type) {
+        case SGSAP_IE_IMSI_TYPE:
+            nas_mobile_identity_imsi = iter->value;
+            nas_mobile_identity_imsi_len = iter->length;
+            break;
+        default:
+            ogs_warn("Invalid Type [%d]", iter->type);
+            break;
+        }
+        iter = iter->next;
+    }
+
+    ogs_tlv_free_all(root);
+
+    if (!nas_mobile_identity_imsi) {
+        ogs_error("No IMSI");
+        sgs_cause = SGSAP_SGS_CAUSE_MISSING_MANDATORY_IE;
+        goto alert_reject;
+    }
+    if (nas_mobile_identity_imsi_len != SGSAP_IE_IMSI_LEN) {
+        ogs_error("Invalid IMSI len [%d]", nas_mobile_identity_imsi_len);
+        sgs_cause = SGSAP_SGS_CAUSE_INVALID_MANDATORY_IE;
+        goto alert_reject;
+    }
+
+    if (nas_mobile_identity_imsi->type != OGS_NAS_MOBILE_IDENTITY_IMSI) {
+        ogs_error("nas_mobile_identity_imsi->type == "
+                    "OGS_NAS_MOBILE_IDENTITY_IMSI");
+        sgs_cause = SGSAP_SGS_CAUSE_INVALID_MANDATORY_IE;
+        goto alert_reject;
+    }
+
+    ogs_nas_eps_imsi_to_bcd(nas_mobile_identity_imsi,
+                            nas_mobile_identity_imsi_len, imsi_bcd);
+    mme_ue = mme_ue_find_by_imsi_bcd(imsi_bcd);
+
+    if (!mme_ue) {
+       ogs_error("No UE(mme-ue) context");
+       sgs_cause = SGSAP_SGS_CAUSE_IMSI_UNKNOWN;
+       goto alert_reject;
+    }
+
+    /* TODO: Set NEAF flag in UE */
+
+    ogs_warn("[SGSAP] Tx ALERT-ACK");
+
+    sgsap_send_to_vlr_with_sid(
+        vlr,
+        sgsap_build_alert_ack(mme_ue),
+        0);
+    return;
+
+alert_reject:
+    ogs_debug("[SGSAP] Tx ALERT-REJECT");
+    ogs_debug("    IMSI[%s]", imsi_bcd);
+
+    sgsap_send_to_vlr_with_sid(
+        vlr,
+        sgsap_build_alert_reject(
+            nas_mobile_identity_imsi, nas_mobile_identity_imsi_len,
+            sgs_cause),
+        0);
+    return;
+}
+
 void sgsap_handle_detach_ack(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf)
 {
     ogs_tlv_t *root = NULL, *iter = NULL;
diff --git a/src/mme/sgsap-handler.h b/src/mme/sgsap-handler.h
index 8d38de64b..16bcc1fb7 100644
--- a/src/mme/sgsap-handler.h
+++ b/src/mme/sgsap-handler.h
@@ -28,6 +28,7 @@ extern "C" {
 
 void sgsap_handle_location_update_accept(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
 void sgsap_handle_location_update_reject(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
+void sgsap_handle_alert_request(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
 void sgsap_handle_detach_ack(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
 void sgsap_handle_paging_request(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
 void sgsap_handle_downlink_unitdata(mme_vlr_t *vlr, ogs_pkbuf_t *pkbuf);
diff --git a/src/mme/sgsap-path.c b/src/mme/sgsap-path.c
index 2fbdfb2b1..f648c4a3a 100644
--- a/src/mme/sgsap-path.c
+++ b/src/mme/sgsap-path.c
@@ -150,6 +150,26 @@ int sgsap_send_tmsi_reallocation_complete(mme_ue_t *mme_ue)
     return rv;
 }
 
+int sgsap_send_ue_activity_indication(mme_ue_t *mme_ue)
+{
+    int rv;
+    ogs_pkbuf_t *pkbuf = NULL;
+    ogs_assert(mme_ue);
+
+    ogs_debug("[SGSAP] Tx UE-ACTIVITY-IND");
+    ogs_debug("    IMSI[%s]", mme_ue->imsi_bcd);
+
+    pkbuf = sgsap_build_ue_activity_indication(mme_ue);
+    if (!pkbuf) {
+        ogs_error("sgsap_build_tmsi_reallocation_complete() failed");
+        return OGS_ERROR;
+    }
+    rv = sgsap_send_to_vlr(mme_ue, pkbuf);
+    ogs_expect(rv == OGS_OK);
+
+    return rv;
+}
+
 int sgsap_send_detach_indication(mme_ue_t *mme_ue)
 {
     int rv;
diff --git a/src/mme/sgsap-path.h b/src/mme/sgsap-path.h
index 897019c9b..65e8fc69e 100644
--- a/src/mme/sgsap-path.h
+++ b/src/mme/sgsap-path.h
@@ -44,6 +44,7 @@ int sgsap_send_to_vlr(mme_ue_t *mme_ue, ogs_pkbuf_t *pkbuf);
 
 int sgsap_send_location_update_request(mme_ue_t *mme_ue);
 int sgsap_send_tmsi_reallocation_complete(mme_ue_t *mme_ue);
+int sgsap_send_ue_activity_indication(mme_ue_t *mme_ue);
 int sgsap_send_detach_indication(mme_ue_t *mme_ue);
 int sgsap_send_mo_csfb_indication(mme_ue_t *mme_ue);
 int sgsap_send_paging_reject(mme_ue_t *mme_ue, uint8_t sgs_cause);
diff --git a/src/mme/sgsap-sm.c b/src/mme/sgsap-sm.c
index ea8db719d..3d390bc46 100644
--- a/src/mme/sgsap-sm.c
+++ b/src/mme/sgsap-sm.c
@@ -153,6 +153,9 @@ void sgsap_state_connected(ogs_fsm_t *s, mme_event_t *e)
         case SGSAP_LOCATION_UPDATE_REJECT:
             sgsap_handle_location_update_reject(vlr, pkbuf);
             break;
+        case SGSAP_ALERT_REQUEST:
+            sgsap_handle_alert_request(vlr, pkbuf);
+            break;
         case SGSAP_EPS_DETACH_ACK:
         case SGSAP_IMSI_DETACH_ACK:
             sgsap_handle_detach_ack(vlr, pkbuf);
diff --git a/src/mme/sgsap-types.h b/src/mme/sgsap-types.h
index fe0ab775d..88e229309 100644
--- a/src/mme/sgsap-types.h
+++ b/src/mme/sgsap-types.h
@@ -33,6 +33,10 @@ extern "C" {
 #define SGSAP_LOCATION_UPDATE_ACCEPT            10
 #define SGSAP_LOCATION_UPDATE_REJECT            11
 #define SGSAP_TMSI_REALLOCATION_COMPLETE        12
+#define SGSAP_ALERT_REQUEST                     13
+#define SGSAP_ALERT_ACK                         14
+#define SGSAP_ALERT_REJECT                      15
+#define SGSAP_UE_ACTIVITY_INDICATION            16
 #define SGSAP_EPS_DETACH_INDICATION             17
 #define SGSAP_EPS_DETACH_ACK                    18
 #define SGSAP_IMSI_DETACH_INDICATION            19