diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1864,6 +1864,14 @@
 				tp->t_dupacks = 0;
 				m_freem(m);
 
+				if (SEQ_GEQ(tp->snd_una, tp->round_end) &&
+				    !ROUND_HAS_ENDED(tp)) {
+				    tp->round_cnt++;
+				    ROUND_END(tp);
+				    if (CC_ALGO(tp)->newround != NULL)
+					CC_ALGO(tp)->newround(&tp->t_ccv, tp->round_cnt);
+				}
+
 				/*
 				 * If all outstanding data are acked, stop
 				 * retransmit timer, otherwise restart timer
@@ -3054,6 +3062,14 @@
 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 			tp->snd_nxt = tp->snd_una;
 
+		if (SEQ_GEQ(tp->snd_una, tp->round_end) &&
+		    !ROUND_HAS_ENDED(tp)) {
+			tp->round_cnt++;
+			ROUND_END(tp);
+			if (CC_ALGO(tp)->newround != NULL)
+				CC_ALGO(tp)->newround(&tp->t_ccv, tp->round_cnt);
+		}
+
 		switch (tp->t_state) {
 		/*
 		 * In FIN_WAIT_1 STATE in addition to the processing
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -1633,6 +1633,12 @@
 		if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
 			tp->snd_max = tp->snd_nxt + xlen;
 	}
+
+	if (ROUND_HAS_ENDED(tp)) {
+	    tp->round_end = tp->snd_max;
+	    ROUND_START(tp);
+	}
+
 	if ((error == 0) &&
 	    (TCPS_HAVEESTABLISHED(tp->t_state) &&
 	     (tp->t_flags & TF_SACK_PERMIT) &&
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -2351,6 +2351,9 @@
 	 * which may match an IPv4-mapped IPv6 address.
 	 */
 	inp->inp_ip_ttl = V_ip_defttl;
+	ROUND_END(tp);
+	tp->round_cnt = 0;
+
 #ifdef TCPPCAP
 	/*
 	 * Init the TCP PCAP queues.
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -381,6 +381,8 @@
 					 */
 	tcp_seq	snd_wl1;		/* window update seg seq number */
 	tcp_seq	snd_wl2;		/* window update seg ack number */
+	uint32_t round_cnt;		/* Number of rounds in the connection */
+	uint32_t round_end;		/* ACK number to receive to end the round */
 
 	tcp_seq	irs;			/* initial receive sequence number */
 	tcp_seq	iss;			/* initial send sequence number */
@@ -855,6 +857,11 @@
 #define	TF2_PROC_SACK_PROHIBIT	0x00100000 /* Due to small MSS size do not process sack's */
 #define	TF2_IPSEC_TSO		0x00200000 /* IPSEC + TSO supported */
 #define	TF2_NO_ISS_CHECK	0x00400000 /* Don't check SEG.ACK against ISS */
+#define	TF2_ROUND_UPDATE	0x00800000 /* Don't check SEG.ACK against ISS */
+
+#define ROUND_HAS_ENDED(tp) (tp->t_flags2 & TF2_ROUND_UPDATE)
+#define ROUND_START(tp) (tp->t_flags2 &= ~TF2_ROUND_UPDATE)
+#define ROUND_END(tp) (tp->t_flags2 |= TF2_ROUND_UPDATE)
 
 /*
  * Structure to hold TCP options that are only used during segment