diff --git a/config.c b/config.c
index 6eb2186..374aee9 100644
--- a/config.c
+++ b/config.c
@@ -81,6 +81,10 @@ static void scan_line(char *s, struct config *cfg)
 
 		pod->announceReceiptTimeout = u8;
 
+	} else if (1 == sscanf(s, " transportSpecific %hhx", &u8)) {
+
+		pod->transportSpecific = u8 << 4;
+
 	} else if (1 == sscanf(s, " tx_timestamp_retries %u", &val)) {
 
 		if (val > 0)
diff --git a/ds.h b/ds.h
index bda0de9..2f31cf3 100644
--- a/ds.h
+++ b/ds.h
@@ -81,6 +81,7 @@ struct port_defaults {
 	Integer8 logSyncInterval;
 	Integer8 logMinDelayReqInterval;
 	UInteger8 announceReceiptTimeout;
+	UInteger8 transportSpecific;
 };
 
 #endif
diff --git a/port.c b/port.c
index e88a7b2..e2fe9cc 100644
--- a/port.c
+++ b/port.c
@@ -70,6 +70,7 @@ struct port {
 	TimeInterval        peerMeanPathDelay;
 	Integer8            logAnnounceInterval;
 	UInteger8           announceReceiptTimeout;
+	UInteger8           transportSpecific;
 	Integer8            logSyncInterval;
 	Enumeration8        delayMechanism;
 	Integer8            logMinPdelayReqInterval;
@@ -376,7 +377,7 @@ static int port_pdelay_request(struct port *p)
 	pdulen = sizeof(struct pdelay_req_msg);
 	msg->hwts.type = p->timestamping;
 
-	msg->header.tsmt               = PDELAY_REQ;
+	msg->header.tsmt               = PDELAY_REQ | p->transportSpecific;
 	msg->header.ver                = PTP_VERSION;
 	msg->header.messageLength      = pdulen;
 	msg->header.domainNumber       = clock_domain_number(p->clock);
@@ -423,7 +424,7 @@ static int port_delay_request(struct port *p)
 	pdulen = sizeof(struct delay_req_msg);
 	msg->hwts.type = p->timestamping;
 
-	msg->header.tsmt               = DELAY_REQ;
+	msg->header.tsmt               = DELAY_REQ | p->transportSpecific;
 	msg->header.ver                = PTP_VERSION;
 	msg->header.messageLength      = pdulen;
 	msg->header.domainNumber       = clock_domain_number(p->clock);
@@ -469,7 +470,7 @@ static int port_tx_announce(struct port *p)
 	pdulen = sizeof(struct announce_msg);
 	msg->hwts.type = p->timestamping;
 
-	msg->header.tsmt               = ANNOUNCE;
+	msg->header.tsmt               = ANNOUNCE | p->transportSpecific;
 	msg->header.ver                = PTP_VERSION;
 	msg->header.messageLength      = pdulen;
 	msg->header.domainNumber       = clock_domain_number(p->clock);
@@ -530,7 +531,7 @@ static int port_tx_sync(struct port *p)
 	pdulen = sizeof(struct sync_msg);
 	msg->hwts.type = p->timestamping;
 
-	msg->header.tsmt               = SYNC;
+	msg->header.tsmt               = SYNC | p->transportSpecific;
 	msg->header.ver                = PTP_VERSION;
 	msg->header.messageLength      = pdulen;
 	msg->header.domainNumber       = clock_domain_number(p->clock);
@@ -563,7 +564,7 @@ static int port_tx_sync(struct port *p)
 	pdulen = sizeof(struct follow_up_msg);
 	fup->hwts.type = p->timestamping;
 
-	fup->header.tsmt               = FOLLOW_UP;
+	fup->header.tsmt               = FOLLOW_UP | p->transportSpecific;
 	fup->header.ver                = PTP_VERSION;
 	fup->header.messageLength      = pdulen;
 	fup->header.domainNumber       = clock_domain_number(p->clock);
@@ -657,6 +658,7 @@ static int port_initialize(struct port *p)
 	p->peerMeanPathDelay       = 0;
 	p->logAnnounceInterval     = p->pod.logAnnounceInterval;
 	p->announceReceiptTimeout  = p->pod.announceReceiptTimeout;
+	p->transportSpecific       = p->pod.transportSpecific;
 	p->logSyncInterval         = p->pod.logSyncInterval;
 	p->logMinPdelayReqInterval = LOG_MIN_PDELAY_REQ_INTERVAL;
 
@@ -786,7 +788,7 @@ static int process_delay_req(struct port *p, struct ptp_message *m)
 	pdulen = sizeof(struct delay_resp_msg);
 	msg->hwts.type = p->timestamping;
 
-	msg->header.tsmt               = DELAY_RESP;
+	msg->header.tsmt               = DELAY_RESP | p->transportSpecific;
 	msg->header.ver                = PTP_VERSION;
 	msg->header.messageLength      = pdulen;
 	msg->header.domainNumber       = m->header.domainNumber;
@@ -913,7 +915,7 @@ static int process_pdelay_req(struct port *p, struct ptp_message *m)
 	rsp_len = sizeof(struct pdelay_resp_msg);
 	rsp->hwts.type = p->timestamping;
 
-	rsp->header.tsmt               = PDELAY_RESP;
+	rsp->header.tsmt               = PDELAY_RESP | p->transportSpecific;
 	rsp->header.ver                = PTP_VERSION;
 	rsp->header.messageLength      = rsp_len;
 	rsp->header.domainNumber       = m->header.domainNumber;
@@ -934,7 +936,7 @@ static int process_pdelay_req(struct port *p, struct ptp_message *m)
 	fup_len = sizeof(struct pdelay_resp_fup_msg);
 	fup->hwts.type = p->timestamping;
 
-	fup->header.tsmt               = PDELAY_RESP_FOLLOW_UP;
+	fup->header.tsmt               = PDELAY_RESP_FOLLOW_UP | p->transportSpecific;
 	fup->header.ver                = PTP_VERSION;
 	fup->header.messageLength      = fup_len;
 	fup->header.domainNumber       = m->header.domainNumber;
diff --git a/ptp4l.c b/ptp4l.c
index 9cd219b..2a0387a 100644
--- a/ptp4l.c
+++ b/ptp4l.c
@@ -207,6 +207,7 @@ int main(int argc, char *argv[])
 	pod.logSyncInterval = 0;
 	pod.logMinDelayReqInterval = 0;
 	pod.announceReceiptTimeout = 3;
+	pod.transportSpecific = 0;
 
 	if (generate_clock_identity(&ds.clockIdentity, iface[0].name)) {
 		fprintf(stderr, "failed to generate a clock identity\n");