diff --git a/phc2sys.c b/phc2sys.c
index eed2171..3af1e51 100644
--- a/phc2sys.c
+++ b/phc2sys.c
@@ -41,6 +41,7 @@
 #include "ds.h"
 #include "fsm.h"
 #include "missing.h"
+#include "notification.h"
 #include "phc.h"
 #include "pi.h"
 #include "pmc_common.h"
@@ -59,12 +60,19 @@
 
 #define PHC_PPS_OFFSET_LIMIT 10000000
 #define PMC_UPDATE_INTERVAL (60 * NS_PER_SEC)
+#define PMC_SUBSCRIBE_DURATION 180	/* 3 minutes */
+/* Note that PMC_SUBSCRIBE_DURATION has to be longer than
+ * PMC_UPDATE_INTERVAL otherwise subscription will time out before it is
+ * renewed.
+ */
 
 struct clock {
 	LIST_ENTRY(clock) list;
 	clockid_t clkid;
 	int sysoff_supported;
 	int is_utc;
+	int state;
+	int new_state;
 	struct servo *servo;
 	enum servo_state servo_state;
 	char *device;
@@ -78,6 +86,7 @@ struct clock {
 struct port {
 	LIST_ENTRY(port) list;
 	unsigned int number;
+	int state;
 	struct clock *clock;
 };
 
@@ -95,6 +104,7 @@ struct node {
 	struct pmc *pmc;
 	int pmc_ds_requested;
 	uint64_t pmc_last_update;
+	int state_changed;
 	LIST_HEAD(port_head, port) ports;
 	LIST_HEAD(clock_head, clock) clocks;
 	struct clock *master;
@@ -533,6 +543,81 @@ static void *get_mgt_data(struct ptp_message *msg)
 	return mgt->data;
 }
 
+static int normalize_state(int state)
+{
+	if (state != PS_MASTER && state != PS_SLAVE &&
+	    state != PS_PRE_MASTER && state != PS_UNCALIBRATED) {
+		/* treat any other state as "not a master nor a slave" */
+		state = PS_DISABLED;
+	}
+	return state;
+}
+
+static int clock_compute_state(struct node *node, struct clock *clock)
+{
+	struct port *p;
+	int state = PS_DISABLED;
+
+	LIST_FOREACH(p, &node->ports, list) {
+		if (p->clock != clock)
+			continue;
+		/* PS_SLAVE takes the highest precedence, PS_UNCALIBRATED
+		 * after that, PS_MASTER is third, PS_PRE_MASTER fourth and
+		 * all of that overrides PS_DISABLED, which corresponds
+		 * nicely with the numerical values */
+		if (p->state > state)
+			state = p->state;
+	}
+	return state;
+}
+
+static int recv_subscribed(struct node *node, struct ptp_message *msg,
+			   int excluded)
+{
+	int mgt_id, state;
+	struct portDS *pds;
+	struct port *port;
+	struct clock *clock;
+
+	mgt_id = get_mgt_id(msg);
+	if (mgt_id == excluded)
+		return 0;
+	switch (mgt_id) {
+	case PORT_DATA_SET:
+		pds = get_mgt_data(msg);
+		port = port_get(node, pds->portIdentity.portNumber);
+		if (!port) {
+			pr_info("received data for unknown port %s",
+				pid2str(&pds->portIdentity));
+			return 1;
+		}
+		state = normalize_state(pds->portState);
+		if (port->state != state) {
+			pr_info("port %s changed state",
+				pid2str(&pds->portIdentity));
+			port->state = state;
+			clock = port->clock;
+			state = clock_compute_state(node, clock);
+			if (clock->state != state) {
+				clock->new_state = state;
+				node->state_changed = 1;
+			}
+		}
+		return 1;
+	}
+	return 0;
+}
+
+static void send_subscription(struct node *node)
+{
+	struct subscribe_events_np sen;
+
+	memset(&sen, 0, sizeof(sen));
+	sen.duration = PMC_SUBSCRIBE_DURATION;
+	sen.bitmask[0] = 1 << NOTIFY_PORT_STATE;
+	pmc_send_set_action(node->pmc, SUBSCRIBE_EVENTS_NP, &sen, sizeof(sen));
+}
+
 static int init_pmc(struct node *node, int domain_number)
 {
 	node->pmc = pmc_create(TRANS_UDS, "/var/run/phc2sys", 0,
@@ -555,7 +640,7 @@ static int run_pmc(struct node *node, int timeout, int ds_id,
 	while (1) {
 		pollfd[0].fd = pmc_get_transport_fd(node->pmc);
 		pollfd[0].events = POLLIN|POLLPRI;
-		if (!node->pmc_ds_requested)
+		if (!node->pmc_ds_requested && ds_id >= 0)
 			pollfd[0].events |= POLLOUT;
 
 		cnt = poll(pollfd, N_FD, timeout);
@@ -572,7 +657,14 @@ static int run_pmc(struct node *node, int timeout, int ds_id,
 		/* Send a new request if there are no pending messages. */
 		if ((pollfd[0].revents & POLLOUT) &&
 		    !(pollfd[0].revents & (POLLIN|POLLPRI))) {
-			pmc_send_get_action(node->pmc, ds_id);
+			switch (ds_id) {
+			case SUBSCRIBE_EVENTS_NP:
+				send_subscription(node);
+				break;
+			default:
+				pmc_send_get_action(node->pmc, ds_id);
+				break;
+			}
 			node->pmc_ds_requested = 1;
 		}
 
@@ -585,6 +677,7 @@ static int run_pmc(struct node *node, int timeout, int ds_id,
 			continue;
 
 		if (!is_msg_mgt(*msg) ||
+		    recv_subscribed(node, *msg, ds_id) ||
 		    get_mgt_id(*msg) != ds_id) {
 			msg_put(*msg);
 			*msg = NULL;
@@ -645,6 +738,25 @@ static int run_pmc_get_utc_offset(struct node *node, int timeout)
 	return 1;
 }
 
+static int run_pmc_subscribe(struct node *node, int timeout)
+{
+	struct ptp_message *msg;
+	int res;
+
+	res = run_pmc(node, timeout, SUBSCRIBE_EVENTS_NP, &msg);
+	if (res <= 0)
+		return res;
+	msg_put(msg);
+	return 1;
+}
+
+static void run_pmc_events(struct node *node)
+{
+	struct ptp_message *msg;
+
+	run_pmc(node, 0, -1, &msg);
+}
+
 static void close_pmc(struct node *node)
 {
 	pmc_destroy(node->pmc);