diff --git a/openbsc/include/openbsc/gsm_04_11.h b/openbsc/include/openbsc/gsm_04_11.h
index 149de90..017c887 100644
--- a/openbsc/include/openbsc/gsm_04_11.h
+++ b/openbsc/include/openbsc/gsm_04_11.h
@@ -39,4 +39,9 @@
 void gsm411_sapi_n_reject(struct gsm_subscriber_connection *conn);
 
 uint8_t sms_next_rp_msg_ref(uint8_t *next_rp_ref);
+
+int gsm411_send_rp_ack(struct gsm_trans *trans, uint8_t msg_ref);
+int gsm411_send_rp_error(struct gsm_trans *trans, uint8_t msg_ref,
+			 uint8_t cause);
+
 #endif
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 1d90eee..6d814c8 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -429,6 +429,11 @@
 	enum gsm_sms_source_id source;
 
 	struct {
+		uint8_t transaction_id;
+		uint32_t msg_ref;
+	} gsm411;
+
+	struct {
 		struct osmo_esme *esme;
 		uint32_t sequence_nr;
 		int transaction_mode;
diff --git a/openbsc/src/libmsc/gsm_04_11.c b/openbsc/src/libmsc/gsm_04_11.c
index a94b971..aa2030f 100644
--- a/openbsc/src/libmsc/gsm_04_11.c
+++ b/openbsc/src/libmsc/gsm_04_11.c
@@ -278,7 +278,7 @@
 }
 
 int sms_route_mt_sms(struct gsm_subscriber_connection *conn, struct msgb *msg,
-			struct gsm_sms *gsms, uint8_t sms_mti)
+		     struct gsm_sms *gsms, uint8_t sms_mti, bool *deferred)
 {
 	int rc;
 
@@ -292,7 +292,7 @@
 	 * delivery of the SMS.
 	 */
 	if (smpp_first) {
-		rc = smpp_try_deliver(gsms, conn);
+		rc = smpp_try_deliver(gsms, conn, deferred);
 		if (rc == GSM411_RP_CAUSE_MO_NUM_UNASSIGNED)
 			goto try_local;
 		if (rc < 0) {
@@ -320,7 +320,7 @@
 			return GSM411_RP_CAUSE_MO_NUM_UNASSIGNED;
 		}
 
-		rc = smpp_try_deliver(gsms, conn);
+		rc = smpp_try_deliver(gsms, conn, deferred);
 		if (rc == GSM411_RP_CAUSE_MO_NUM_UNASSIGNED) {
 			rate_ctr_inc(&conn->network->msc_ctrs->ctr[MSC_CTR_SMS_NO_RECEIVER]);
 		} else if (rc < 0) {
@@ -363,8 +363,10 @@
 
 /* process an incoming TPDU (called from RP-DATA)
  * return value > 0: RP CAUSE for ERROR; < 0: silent error; 0 = success */
-static int gsm340_rx_tpdu(struct gsm_subscriber_connection *conn, struct msgb *msg)
+static int gsm340_rx_tpdu(struct gsm_trans *trans, struct msgb *msg,
+			  uint32_t gsm411_msg_ref, bool *deferred)
 {
+	struct gsm_subscriber_connection *conn = trans->conn;
 	uint8_t *smsp = msgb_sms(msg);
 	struct gsm_sms *gsms;
 	unsigned int sms_alphabet;
@@ -395,6 +397,9 @@
 	smsp++;
 	gsms->msg_ref = *smsp++;
 
+	gsms->gsm411.transaction_id = trans->transaction_id;
+	gsms->gsm411.msg_ref = gsm411_msg_ref;
+
 	/* length in bytes of the destination address */
 	da_len_bytes = 2 + *smsp/2 + *smsp%2;
 	if (da_len_bytes > 12) {
@@ -481,9 +486,10 @@
 	/* FIXME: This looks very wrong */
 	send_signal(0, NULL, gsms, 0);
 
-	rc = sms_route_mt_sms(conn, msg, gsms, sms_mti);
+	rc = sms_route_mt_sms(conn, msg, gsms, sms_mti, deferred);
 out:
-	sms_free(gsms);
+	if (!deferred)
+		sms_free(gsms);
 
 	return rc;
 }
@@ -505,7 +511,7 @@
 	return gsm411_smr_send(inst, rl_msg_type, msg);
 }
 
-static int gsm411_send_rp_ack(struct gsm_trans *trans, uint8_t msg_ref)
+int gsm411_send_rp_ack(struct gsm_trans *trans, uint8_t msg_ref)
 {
 	struct msgb *msg = gsm411_msgb_alloc();
 
@@ -515,8 +521,8 @@
 		msg_ref, GSM411_SM_RL_REPORT_REQ);
 }
 
-static int gsm411_send_rp_error(struct gsm_trans *trans,
-				uint8_t msg_ref, uint8_t cause)
+int gsm411_send_rp_error(struct gsm_trans *trans, uint8_t msg_ref,
+			 uint8_t cause)
 {
 	struct msgb *msg = gsm411_msgb_alloc();
 
@@ -536,6 +542,7 @@
 			  uint8_t dst_len, uint8_t *dst,
 			  uint8_t tpdu_len, uint8_t *tpdu)
 {
+	bool deferred = false;
 	int rc = 0;
 
 	if (src_len && src)
@@ -552,8 +559,8 @@
 
 	DEBUGP(DLSMS, "DST(%u,%s)\n", dst_len, osmo_hexdump(dst, dst_len));
 
-	rc = gsm340_rx_tpdu(trans->conn, msg);
-	if (rc == 0)
+	rc = gsm340_rx_tpdu(trans, msg, rph->msg_ref, &deferred);
+	if (rc == 0 && !deferred)
 		return gsm411_send_rp_ack(trans, rph->msg_ref);
 	else if (rc > 0)
 		return gsm411_send_rp_error(trans, rph->msg_ref, rc);
diff --git a/openbsc/src/libmsc/smpp_openbsc.c b/openbsc/src/libmsc/smpp_openbsc.c
index ec9dda3..8f1a96c 100644
--- a/openbsc/src/libmsc/smpp_openbsc.c
+++ b/openbsc/src/libmsc/smpp_openbsc.c
@@ -44,6 +44,7 @@
 #include <openbsc/signal.h>
 #include <openbsc/transaction.h>
 #include <openbsc/gsm_subscriber.h>
+#include <openbsc/chan_alloc.h>
 
 #include "smpp_smsc.h"
 
@@ -460,12 +461,122 @@
 	}
 }
 
+static void smpp_cmd_free(struct osmo_smpp_cmd *cmd)
+{
+	osmo_timer_del(&cmd->response_timer);
+	llist_del(&cmd->list);
+	subscr_put(cmd->subscr);
+	sms_free(cmd->sms);
+	talloc_free(cmd);
+}
+
+void smpp_cmd_flush_pending(struct osmo_esme *esme)
+{
+	struct osmo_smpp_cmd *cmd, *next;
+
+	llist_for_each_entry_safe(cmd, next, &esme->smpp_cmd_list, list)
+		smpp_cmd_free(cmd);
+}
+
+void smpp_cmd_ack(struct osmo_smpp_cmd *cmd)
+{
+	struct gsm_subscriber_connection *conn;
+	struct gsm_trans *trans;
+
+	conn = connection_for_subscr(cmd->subscr);
+	if (!conn) {
+		LOGP(DSMPP, LOGL_ERROR, "No connection to subscriber anymore\n");
+		return;
+	}
+
+	trans = trans_find_by_id(conn, GSM48_PDISC_SMS,
+				 cmd->sms->gsm411.transaction_id);
+	if (!trans) {
+		LOGP(DSMPP, LOGL_ERROR, "GSM transaction %u is gone\n",
+		     cmd->sms->gsm411.transaction_id);
+		return;
+	}
+
+	gsm411_send_rp_ack(trans, cmd->sms->gsm411.msg_ref);
+	smpp_cmd_free(cmd);
+}
+
+void smpp_cmd_err(struct osmo_smpp_cmd *cmd)
+{
+	struct gsm_subscriber_connection *conn;
+	struct gsm_trans *trans;
+
+	conn = connection_for_subscr(cmd->subscr);
+	if (!conn) {
+		LOGP(DSMPP, LOGL_ERROR, "No connection to subscriber anymore\n");
+		return;
+	}
+
+	trans = trans_find_by_id(conn, GSM48_PDISC_SMS,
+				 cmd->sms->gsm411.transaction_id);
+	if (!trans) {
+		LOGP(DSMPP, LOGL_ERROR, "GSM transaction %u is gone\n",
+		     cmd->sms->gsm411.transaction_id);
+		return;
+	}
+
+	gsm411_send_rp_error(trans, cmd->sms->gsm411.msg_ref,
+			     GSM411_RP_CAUSE_MO_NET_OUT_OF_ORDER);
+	smpp_cmd_free(cmd);
+}
+
+static void smpp_deliver_sm_cb(void *data)
+{
+	smpp_cmd_err(data);
+}
+
+static int smpp_cmd_enqueue(struct osmo_esme *esme,
+			    struct gsm_subscriber *subscr, struct gsm_sms *sms,
+			    uint32_t sequence_number, bool *deferred)
+{
+	struct osmo_smpp_cmd *cmd;
+
+	cmd = talloc_zero(esme, struct osmo_smpp_cmd);
+	if (!cmd)
+		return -1;
+
+	cmd->sequence_nr	= sequence_number;
+	cmd->sms		= sms;
+	cmd->subscr		= subscr_get(subscr);
+
+	/* FIXME: No predefined value for this response_timer as specified by
+	 * SMPP 3.4 specs, section 7.2. Make this configurable? Don't forget
+	 * lchan keeps busy until we get a reply to this SMPP command. Too high
+	 * value may exhaust resources.
+	 */
+	cmd->response_timer.cb	= smpp_deliver_sm_cb;
+	cmd->response_timer.data = cmd;
+	osmo_timer_schedule(&cmd->response_timer, 5, 0);
+	llist_add_tail(&cmd->list, &esme->smpp_cmd_list);
+	*deferred = true;
+
+	return 0;
+}
+
+struct osmo_smpp_cmd *smpp_cmd_find_by_seqnum(struct osmo_esme *esme,
+					      uint32_t sequence_nr)
+{
+	struct osmo_smpp_cmd *cmd;
+
+	llist_for_each_entry(cmd, &esme->smpp_cmd_list, list) {
+		if (cmd->sequence_nr == sequence_nr)
+			return cmd;
+	}
+	return NULL;
+}
+
 static int deliver_to_esme(struct osmo_esme *esme, struct gsm_sms *sms,
-			   struct gsm_subscriber_connection *conn)
+			   struct gsm_subscriber_connection *conn,
+			   bool *deferred)
 {
 	struct deliver_sm_t deliver;
+	int mode, ret;
 	uint8_t dcs;
-	int mode;
 
 	memset(&deliver, 0, sizeof(deliver));
 	deliver.command_length	= 0;
@@ -537,7 +648,12 @@
 	if (esme->acl && esme->acl->osmocom_ext && conn->lchan)
 		append_osmo_tlvs(&deliver.tlv, conn->lchan);
 
-	return smpp_tx_deliver(esme, &deliver);
+	ret = smpp_tx_deliver(esme, &deliver);
+	if (ret < 0)
+		return ret;
+
+	return smpp_cmd_enqueue(esme, conn->subscr, sms,
+				deliver.sequence_number, deferred);
 }
 
 static struct smsc *g_smsc;
@@ -547,7 +663,8 @@
 	return g_smsc->smpp_first;
 }
 
-int smpp_try_deliver(struct gsm_sms *sms, struct gsm_subscriber_connection *conn)
+int smpp_try_deliver(struct gsm_sms *sms,
+		     struct gsm_subscriber_connection *conn, bool *deferred)
 {
 	struct osmo_esme *esme;
 	struct osmo_smpp_addr dst;
@@ -561,7 +678,7 @@
 	if (!esme)
 		return GSM411_RP_CAUSE_MO_NUM_UNASSIGNED;
 
-	return deliver_to_esme(esme, sms, conn);
+	return deliver_to_esme(esme, sms, conn, deferred);
 }
 
 struct smsc *smsc_from_vty(struct vty *v)
diff --git a/openbsc/src/libmsc/smpp_smsc.c b/openbsc/src/libmsc/smpp_smsc.c
index e537490..bd25918 100644
--- a/openbsc/src/libmsc/smpp_smsc.c
+++ b/openbsc/src/libmsc/smpp_smsc.c
@@ -247,6 +247,7 @@
 		osmo_fd_unregister(&esme->wqueue.bfd);
 		close(esme->wqueue.bfd.fd);
 	}
+	smpp_cmd_flush_pending(esme);
 	llist_del(&esme->list);
 	talloc_free(esme);
 }
@@ -660,6 +661,7 @@
 static int smpp_handle_deliver_resp(struct osmo_esme *esme, struct msgb *msg)
 {
 	struct deliver_sm_resp_t deliver_r;
+	struct osmo_smpp_cmd *cmd;
 	int rc;
 
 	memset(&deliver_r, 0, sizeof(deliver_r));
@@ -671,6 +673,20 @@
 		return rc;
 	}
 
+	cmd = smpp_cmd_find_by_seqnum(esme, deliver_r.sequence_number);
+	if (!cmd) {
+		LOGP(DSMPP, LOGL_ERROR, "[%s] Rx DELIVER-SM RESP !? (%s)\n",
+			esme->system_id, get_value_string(smpp_status_strs,
+						  deliver_r.command_status));
+		return -1;
+	}
+
+	/* Map SMPP command status to GSM 04.11 cause? */
+	if (deliver_r.command_status == ESME_ROK)
+		smpp_cmd_ack(cmd);
+	else
+		smpp_cmd_err(cmd);
+
 	LOGP(DSMPP, LOGL_INFO, "[%s] Rx DELIVER-SM RESP (%s)\n",
 		esme->system_id, get_value_string(smpp_status_strs,
 						  deliver_r.command_status));
@@ -889,6 +905,7 @@
 		return -ENOMEM;
 	}
 
+	INIT_LLIST_HEAD(&esme->smpp_cmd_list);
 	smpp_esme_get(esme);
 	esme->own_seq_nr = rand();
 	esme_inc_seq_nr(esme);
diff --git a/openbsc/src/libmsc/smpp_smsc.h b/openbsc/src/libmsc/smpp_smsc.h
index bd20137..b95a1f5 100644
--- a/openbsc/src/libmsc/smpp_smsc.h
+++ b/openbsc/src/libmsc/smpp_smsc.h
@@ -7,6 +7,7 @@
 #include <osmocom/core/utils.h>
 #include <osmocom/core/msgb.h>
 #include <osmocom/core/write_queue.h>
+#include <osmocom/core/timer.h>
 
 #include <smpp34.h>
 #include <smpp34_structs.h>
@@ -37,6 +38,8 @@
 	struct osmo_smpp_acl *acl;
 	int use;
 
+	struct llist_head smpp_cmd_list;
+
 	uint32_t own_seq_nr;
 
 	struct osmo_wqueue wqueue;
@@ -83,6 +86,19 @@
 	} u;
 };
 
+struct osmo_smpp_cmd {
+	struct llist_head	list;
+	struct gsm_subscriber	*subscr;
+	struct gsm_sms		*sms;
+	uint32_t		sequence_nr;
+	struct osmo_timer_list	response_timer;
+};
+
+struct osmo_smpp_cmd *smpp_cmd_find_by_seqnum(struct osmo_esme *esme,
+					      uint32_t sequence_number);
+void smpp_cmd_ack(struct osmo_smpp_cmd *cmd);
+void smpp_cmd_err(struct osmo_smpp_cmd *cmd);
+void smpp_cmd_flush_pending(struct osmo_esme *esme);
 
 struct smsc {
 	struct osmo_fd listen_ofd;
@@ -146,5 +162,5 @@
 int smpp_route_smpp_first(struct gsm_sms *sms,
 			    struct gsm_subscriber_connection *conn);
 int smpp_try_deliver(struct gsm_sms *sms,
-			    struct gsm_subscriber_connection *conn);
+		     struct gsm_subscriber_connection *conn, bool *deferred);
 #endif