diff --git a/src/octoi/e1oip.c b/src/octoi/e1oip.c
index 608a5e0..19eb3bf 100644
--- a/src/octoi/e1oip.c
+++ b/src/octoi/e1oip.c
@@ -66,7 +66,7 @@ static const struct rate_ctr_group_desc iline_ctrg_desc = {
 };
 
 static const struct osmo_stat_item_desc iline_stat_description[] = {
-	[LINE_STAT_E1oIP_RTT] = { "e1oip:rtt", "Round Trip Time (in ms)" },
+	[LINE_STAT_E1oIP_RTT] = { "e1oip:rtt", "Round Trip Time (in us)" },
 	[LINE_STAT_E1oIP_E1O_FIFO] = { "e1oip:e1o_fifo_level", "E1 originated FIFO level" },
 	[LINE_STAT_E1oIP_E1T_FIFO] = { "e1oip:e1t_fifo_level", "E1 terminated FIFO level" },
 	[LINE_STAT_E1oIP_E1O_TS] = { "e1oip:e1o_ts_active", "E1 timeslots active in E1->IP direction" },
diff --git a/src/octoi/octoi_clnt_fsm.c b/src/octoi/octoi_clnt_fsm.c
index 441f904..c4117d2 100644
--- a/src/octoi/octoi_clnt_fsm.c
+++ b/src/octoi/octoi_clnt_fsm.c
@@ -46,6 +46,12 @@ struct clnt_state {
 	struct osmo_timer_list rx_alive_timer;
 	struct octoi_account *acc;
 
+	struct {
+		struct osmo_timer_list timer;
+		struct timespec last_tx_ts;
+		uint16_t last_tx_seq;
+	} echo_req;
+
 	/* fields below are all filled in once received from the remote server side */
 	struct {
 		char *server_id;
@@ -122,6 +128,7 @@ static void clnt_st_accepted_onenter(struct osmo_fsm_inst *fi, uint32_t prev_sta
 
 	st->peer->tdm_permitted = true;
 	osmo_timer_schedule(&st->rx_alive_timer, 3, 0);
+	osmo_timer_schedule(&st->echo_req.timer, 10, 0);
 }
 
 static void clnt_st_accepted(struct osmo_fsm_inst *fi, uint32_t event, void *data)
@@ -143,6 +150,7 @@ static void clnt_st_accepted_onleave(struct osmo_fsm_inst *fi, uint32_t next_sta
 {
 	struct clnt_state *st = fi->priv;
 
+	osmo_timer_del(&st->echo_req.timer);
 	osmo_timer_del(&st->rx_alive_timer);
 	st->peer->tdm_permitted = false;
 }
@@ -210,16 +218,27 @@ static void clnt_allstate_action(struct osmo_fsm_inst *fi, uint32_t event, void
 {
 	struct clnt_state *st = fi->priv;
 	struct msgb *msg = data;
-	struct e1oip_echo *echo_req;
+	struct e1oip_echo *echo_req, *echo_resp;
 	struct e1oip_error_ind *err_ind;
+	int32_t rtt_us;
 
 	switch (event) {
 	case OCTOI_EV_RX_ECHO_REQ:
 		echo_req = msgb_l2(msg);
+		LOGPFSML(fi, LOGL_DEBUG, "Rx OCTOI ECHO_REQ (seq=%u)\n", ntohs(echo_req->seq_nr));
 		octoi_tx_echo_resp(st->peer, ntohs(echo_req->seq_nr), echo_req->data, msgb_l2len(msg));
 		break;
 	case OCTOI_EV_RX_ECHO_RESP:
-		/* FIXME: update state, peer has responded! */
+		echo_resp = msgb_l2(msg);
+		if (ntohs(echo_resp->seq_nr) != st->echo_req.last_tx_seq) {
+			LOGPFSML(fi, LOGL_NOTICE, "Rx OCTOI ECHO RESP (seq=%u) doesn't match our last "
+				 "request (seq=%u)\n", ntohs(echo_resp->seq_nr), st->echo_req.last_tx_seq);
+			break;
+		}
+		rtt_us = ts_us_ago(&st->echo_req.last_tx_ts);
+		iline_stat_set(st->peer->iline, LINE_STAT_E1oIP_RTT, rtt_us);
+		LOGPFSML(fi, LOGL_INFO, "Rx OCTOI ECHO_RESP (seq=%u, rtt=%d)\n",
+			 ntohs(echo_resp->seq_nr), rtt_us);
 		break;
 	case OCTOI_EV_RX_ERROR_IND:
 		err_ind = msgb_l2(msg);
@@ -301,6 +320,17 @@ reconnect:
 	osmo_fsm_inst_state_chg(fi, CLNT_ST_WAIT_RECONNECT, 10, 0);
 }
 
+static void clnt_echo_req_timer_cb(void *data)
+{
+	struct osmo_fsm_inst *fi = data;
+	struct clnt_state *st = fi->priv;
+
+	/* trigger sending of an OCTOI ECHO REQ */
+	clock_gettime(CLOCK_MONOTONIC, &st->echo_req.last_tx_ts);
+	octoi_tx_echo_req(st->peer, ++st->echo_req.last_tx_seq, NULL, 0);
+	LOGPFSML(fi, LOGL_DEBUG, "Tx OCTOI ECHO_REQ (seq=%u)\n", st->echo_req.last_tx_seq);
+	osmo_timer_schedule(&st->echo_req.timer, 10, 0);
+}
 
 /* call-back function for every received OCTOI socket message for given peer */
 int octoi_clnt_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg)
@@ -345,6 +375,7 @@ void octoi_clnt_start_for_peer(struct octoi_peer *peer, struct octoi_account *ac
 		st->service = E1OIP_SERVICE_E1_FRAMED;
 		st->capability_flags = 0;
 		osmo_timer_setup(&st->rx_alive_timer, clnt_rx_alive_timer_cb, fi);
+		osmo_timer_setup(&st->echo_req.timer, clnt_echo_req_timer_cb, fi);
 		fi->priv = st;
 
 		peer->priv = fi;
diff --git a/src/octoi/octoi_fsm.c b/src/octoi/octoi_fsm.c
index 37d0259..39790fa 100644
--- a/src/octoi/octoi_fsm.c
+++ b/src/octoi/octoi_fsm.c
@@ -28,6 +28,19 @@
 #include "octoi_fsm.h"
 #include "e1oip.h"
 
+/* how many microseconds ago was 'old_ts'? */
+int32_t ts_us_ago(const struct timespec *old_ts)
+{
+	struct timespec ts_now, ts_diff;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts_now);
+	timespecsub(&ts_now, old_ts, &ts_diff);
+
+	if (ts_diff.tv_sec > INT32_MAX / 1000000)
+		return INT32_MAX;
+
+	return ts_diff.tv_sec * 1000000 + ts_diff.tv_nsec / 1000;
+}
 
 const struct value_string octoi_fsm_event_names[] = {
 	{ OCTOI_EV_RX_TDM_DATA,		"RX_TDM_DATA" },
diff --git a/src/octoi/octoi_fsm.h b/src/octoi/octoi_fsm.h
index b605c3a..e54afe1 100644
--- a/src/octoi/octoi_fsm.h
+++ b/src/octoi/octoi_fsm.h
@@ -29,3 +29,5 @@ int _octoi_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg);
 /* call-back function for every received OCTOI socket message for given peer */
 int octoi_srv_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg);
 int octoi_clnt_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg);
+
+int32_t ts_us_ago(const struct timespec *old_ts);
diff --git a/src/octoi/octoi_srv_fsm.c b/src/octoi/octoi_srv_fsm.c
index 53b79e7..1af3805 100644
--- a/src/octoi/octoi_srv_fsm.c
+++ b/src/octoi/octoi_srv_fsm.c
@@ -55,6 +55,11 @@ struct srv_state {
 	struct octoi_account *acc;
 	void *app_priv;			/* application private data */
 	const char *rej_str;
+	struct {
+		struct osmo_timer_list timer;
+		struct timespec last_tx_ts;
+		uint16_t last_tx_seq;
+	} echo_req;
 };
 
 static void srv_st_init(struct osmo_fsm_inst *fi, uint32_t event, void *data)
@@ -175,6 +180,7 @@ static void srv_st_accepted_onenter(struct osmo_fsm_inst *fi, uint32_t prev_stat
 
 	st->peer->tdm_permitted = true;
 	osmo_timer_schedule(&st->rx_alive_timer, 3, 0);
+	osmo_timer_schedule(&st->echo_req.timer, 10, 0);
 }
 
 static void srv_st_accepted(struct osmo_fsm_inst *fi, uint32_t event, void *data)
@@ -200,6 +206,7 @@ static void srv_st_accepted_onleave(struct osmo_fsm_inst *fi, uint32_t next_stat
 {
 	struct srv_state *st = fi->priv;
 
+	osmo_timer_del(&st->echo_req.timer);
 	osmo_timer_del(&st->rx_alive_timer);
 	st->peer->tdm_permitted = false;
 }
@@ -277,16 +284,27 @@ static void srv_allstate_action(struct osmo_fsm_inst *fi, uint32_t event, void *
 {
 	struct srv_state *st = fi->priv;
 	struct msgb *msg = data;
-	struct e1oip_echo *echo_req;
+	struct e1oip_echo *echo_req, *echo_resp;
 	struct e1oip_error_ind *err_ind;
+	int32_t rtt_us;
 
 	switch (event) {
 	case OCTOI_EV_RX_ECHO_REQ:
 		echo_req = msgb_l2(msg);
+		LOGPFSML(fi, LOGL_DEBUG, "Rx OCTOI ECHO_REQ (seq=%u)\n", ntohs(echo_req->seq_nr));
 		octoi_tx_echo_resp(st->peer, ntohs(echo_req->seq_nr), echo_req->data, msgb_l2len(msg));
 		break;
 	case OCTOI_EV_RX_ECHO_RESP:
-		/* TODO: update state, peer has responded! */
+		echo_resp = msgb_l2(msg);
+		if (ntohs(echo_resp->seq_nr) != st->echo_req.last_tx_seq) {
+			LOGPFSML(fi, LOGL_NOTICE, "Rx OCTOI ECHO RESP (seq=%u) doesn't match our last "
+				 "request (seq=%u)\n", ntohs(echo_resp->seq_nr), st->echo_req.last_tx_seq);
+			break;
+		}
+		rtt_us = ts_us_ago(&st->echo_req.last_tx_ts);
+		iline_stat_set(st->peer->iline, LINE_STAT_E1oIP_RTT, rtt_us);
+		LOGPFSML(fi, LOGL_INFO, "Rx OCTOI ECHO_RESP (seq=%u, rtt=%d)\n",
+			 ntohs(echo_resp->seq_nr), rtt_us);
 		break;
 	case OCTOI_EV_RX_ERROR_IND:
 		err_ind = msgb_l2(msg);
@@ -316,6 +334,7 @@ static void srv_fsm_cleanup(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause c
 	struct srv_state *st = fi->priv;
 
 	osmo_timer_del(&st->rx_alive_timer);
+	osmo_timer_del(&st->echo_req.timer);
 
 	/* as long as 'fi' lives within 'peer' we cannot recursively destroy peer */
 	talloc_steal(OTC_SELECT, fi);
@@ -377,6 +396,18 @@ term:
 	osmo_fsm_inst_term(fi, OSMO_FSM_TERM_ERROR, NULL);
 }
 
+static void srv_echo_req_timer_cb(void *data)
+{
+	struct osmo_fsm_inst *fi = data;
+	struct srv_state *st = fi->priv;
+
+	/* trigger sending of an OCTOI ECHO REQ */
+	clock_gettime(CLOCK_MONOTONIC, &st->echo_req.last_tx_ts);
+	octoi_tx_echo_req(st->peer, ++st->echo_req.last_tx_seq, NULL, 0);
+	LOGPFSML(fi, LOGL_DEBUG, "Tx OCTOI ECHO_REQ (seq=%u)\n", st->echo_req.last_tx_seq);
+	osmo_timer_schedule(&st->echo_req.timer, 10, 0);
+}
+
 /* call-back function for every received OCTOI socket message for given peer */
 int octoi_srv_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg)
 {
@@ -393,6 +424,7 @@ int octoi_srv_fsm_rx_cb(struct octoi_peer *peer, struct msgb *msg)
 		OSMO_ASSERT(st);
 		st->peer = peer;
 		osmo_timer_setup(&st->rx_alive_timer, srv_rx_alive_timer_cb, fi);
+		osmo_timer_setup(&st->echo_req.timer, srv_echo_req_timer_cb, fi);
 		fi->priv = st;
 
 		peer->priv = fi;