diff --git a/sys/netinet/sctp_input.c b/sys/netinet/sctp_input.c
index f5ea529effca..c07019c965c6 100644
--- a/sys/netinet/sctp_input.c
+++ b/sys/netinet/sctp_input.c
@@ -1969,7 +1969,8 @@ sctp_process_cookie_existing(struct mbuf *m, int iphlen, int offset,
 			asoc->strmout[i].abandoned_unsent[0] = 0;
 #endif
 			stcb->asoc.strmout[i].stream_no = i;
-			stcb->asoc.strmout[i].next_sequence_send = 0;
+			stcb->asoc.strmout[i].next_mid_ordered = 0;
+			stcb->asoc.strmout[i].next_mid_unordered = 0;
 			stcb->asoc.strmout[i].last_msg_incomplete = 0;
 		}
 		/* process the INIT-ACK info (my info) */
@@ -3521,11 +3522,13 @@ sctp_reset_out_streams(struct sctp_tcb *stcb, uint32_t number_entries, uint16_t
 				/* no such stream */
 				continue;
 			}
-			stcb->asoc.strmout[temp].next_sequence_send = 0;
+			stcb->asoc.strmout[temp].next_mid_ordered = 0;
+			stcb->asoc.strmout[temp].next_mid_unordered = 0;
 		}
 	} else {
 		for (i = 0; i < stcb->asoc.streamoutcnt; i++) {
-			stcb->asoc.strmout[i].next_sequence_send = 0;
+			stcb->asoc.strmout[i].next_mid_ordered = 0;
+			stcb->asoc.strmout[i].next_mid_unordered = 0;
 		}
 	}
 	sctp_ulp_notify(SCTP_NOTIFY_STR_RESET_SEND, stcb, number_entries, (void *)list, SCTP_SO_NOT_LOCKED);
diff --git a/sys/netinet/sctp_output.c b/sys/netinet/sctp_output.c
index 6d71f7d1e653..3544d6942ce0 100644
--- a/sys/netinet/sctp_output.c
+++ b/sys/netinet/sctp_output.c
@@ -3643,7 +3643,8 @@ sctp_process_cmsgs_for_init(struct sctp_tcb *stcb, struct mbuf *control, int *er
 					for (i = 0; i < stcb->asoc.streamoutcnt; i++) {
 						TAILQ_INIT(&stcb->asoc.strmout[i].outqueue);
 						stcb->asoc.strmout[i].chunks_on_queues = 0;
-						stcb->asoc.strmout[i].next_sequence_send = 0;
+						stcb->asoc.strmout[i].next_mid_ordered = 0;
+						stcb->asoc.strmout[i].next_mid_unordered = 0;
 #if defined(SCTP_DETAILED_STR_STATS)
 						for (j = 0; j < SCTP_PR_SCTP_MAX + 1; j++) {
 							stcb->asoc.strmout[i].abandoned_sent[j] = 0;
@@ -6381,7 +6382,6 @@ sctp_msg_append(struct sctp_tcb *stcb,
 	sp->ppid = srcv->sinfo_ppid;
 	sp->context = srcv->sinfo_context;
 	sp->fsn = 0;
-	sp->msg_id = atomic_fetchadd_int(&stcb->asoc.assoc_msg_id, 1);
 	if (sp->sinfo_flags & SCTP_ADDR_OVER) {
 		sp->net = net;
 		atomic_add_int(&sp->net->ref_count, 1);
@@ -7568,10 +7568,28 @@ sctp_move_to_outqueue(struct sctp_tcb *stcb,
 	chk->asoc = &stcb->asoc;
 	chk->pad_inplace = 0;
 	chk->no_fr_allowed = 0;
-	chk->rec.data.stream_seq = strq->next_sequence_send;
-	if ((rcv_flags & SCTP_DATA_LAST_FRAG) &&
-	    !(rcv_flags & SCTP_DATA_UNORDERED)) {
-		strq->next_sequence_send++;
+	if (stcb->asoc.idata_supported == 0) {
+		if (rcv_flags & SCTP_DATA_UNORDERED) {
+			/* Just use 0. The receiver ignores the values. */
+			chk->rec.data.stream_seq = 0;
+		} else {
+			chk->rec.data.stream_seq = strq->next_mid_ordered;
+			if (rcv_flags & SCTP_DATA_LAST_FRAG) {
+				strq->next_mid_ordered++;
+			}
+		}
+	} else {
+		if (rcv_flags & SCTP_DATA_UNORDERED) {
+			chk->rec.data.stream_seq = strq->next_mid_unordered;
+			if (rcv_flags & SCTP_DATA_LAST_FRAG) {
+				strq->next_mid_unordered++;
+			}
+		} else {
+			chk->rec.data.stream_seq = strq->next_mid_ordered;
+			if (rcv_flags & SCTP_DATA_LAST_FRAG) {
+				strq->next_mid_ordered++;
+			}
+		}
 	}
 	chk->rec.data.stream_number = sp->stream;
 	chk->rec.data.payloadtype = sp->ppid;
@@ -7630,7 +7648,7 @@ sctp_move_to_outqueue(struct sctp_tcb *stcb,
 		dchkh->ch.chunk_flags = chk->rec.data.rcv_flags;
 		dchkh->dp.tsn = htonl(chk->rec.data.TSN_seq);
 		dchkh->dp.stream_id = htons((strq->stream_no & 0x0000ffff));
-		dchkh->dp.stream_sequence = htons(chk->rec.data.stream_seq);
+		dchkh->dp.stream_sequence = htons((uint16_t) chk->rec.data.stream_seq);
 		dchkh->dp.protocol_id = chk->rec.data.payloadtype;
 		dchkh->ch.chunk_length = htons(chk->send_size);
 	} else {
@@ -7638,9 +7656,8 @@ sctp_move_to_outqueue(struct sctp_tcb *stcb,
 		ndchkh->ch.chunk_flags = chk->rec.data.rcv_flags;
 		ndchkh->dp.tsn = htonl(chk->rec.data.TSN_seq);
 		ndchkh->dp.stream_id = htons(strq->stream_no);
-		/* WHAT DO WE DO HERE??? */
 		ndchkh->dp.reserved = htons(0);
-		ndchkh->dp.msg_id = htonl(sp->msg_id);
+		ndchkh->dp.msg_id = htonl(chk->rec.data.stream_seq);
 		if (sp->fsn == 0)
 			ndchkh->dp.ppid_fsn.protocol_id = chk->rec.data.payloadtype;
 		else
@@ -12235,7 +12252,8 @@ sctp_send_str_reset_req(struct sctp_tcb *stcb,
 		for (i = 0; i < stcb->asoc.streamoutcnt; i++) {
 			TAILQ_INIT(&stcb->asoc.strmout[i].outqueue);
 			stcb->asoc.strmout[i].chunks_on_queues = oldstream[i].chunks_on_queues;
-			stcb->asoc.strmout[i].next_sequence_send = oldstream[i].next_sequence_send;
+			stcb->asoc.strmout[i].next_mid_ordered = oldstream[i].next_mid_ordered;
+			stcb->asoc.strmout[i].next_mid_unordered = oldstream[i].next_mid_unordered;
 			stcb->asoc.strmout[i].last_msg_incomplete = oldstream[i].last_msg_incomplete;
 			stcb->asoc.strmout[i].stream_no = i;
 			stcb->asoc.strmout[i].state = oldstream[i].state;
@@ -12267,7 +12285,8 @@ sctp_send_str_reset_req(struct sctp_tcb *stcb,
 			stcb->asoc.strmout[i].abandoned_sent[0] = 0;
 			stcb->asoc.strmout[i].abandoned_unsent[0] = 0;
 #endif
-			stcb->asoc.strmout[i].next_sequence_send = 0x0;
+			stcb->asoc.strmout[i].next_mid_ordered = 0;
+			stcb->asoc.strmout[i].next_mid_unordered = 0;
 			stcb->asoc.strmout[i].stream_no = i;
 			stcb->asoc.strmout[i].last_msg_incomplete = 0;
 			stcb->asoc.ss_functions.sctp_ss_init_stream(&stcb->asoc.strmout[i], NULL);
@@ -12425,7 +12444,6 @@ sctp_copy_it_in(struct sctp_tcb *stcb,
 	sp->ppid = srcv->sinfo_ppid;
 	sp->context = srcv->sinfo_context;
 	sp->fsn = 0;
-	sp->msg_id = atomic_fetchadd_int(&stcb->asoc.assoc_msg_id, 1);
 	(void)SCTP_GETTIME_TIMEVAL(&sp->ts);
 
 	sp->stream = srcv->sinfo_stream;
diff --git a/sys/netinet/sctp_structs.h b/sys/netinet/sctp_structs.h
index c64d2b6c4feb..ad9d9783a4ab 100644
--- a/sys/netinet/sctp_structs.h
+++ b/sys/netinet/sctp_structs.h
@@ -522,7 +522,6 @@ struct sctp_stream_queue_pending {
 	          TAILQ_ENTRY(sctp_stream_queue_pending) next;
 	          TAILQ_ENTRY(sctp_stream_queue_pending) ss_next;
 	uint32_t fsn;
-	uint32_t msg_id;
 	uint32_t length;
 	uint32_t timetolive;
 	uint32_t ppid;
@@ -619,7 +618,12 @@ struct sctp_stream_out {
 	uint32_t abandoned_unsent[1];
 	uint32_t abandoned_sent[1];
 #endif
-	uint32_t next_sequence_send;	/* next one I expect to send out */
+	/*
+	 * For associations using DATA chunks, the lower 16-bit of
+	 * next_mid_ordered are used as the next SSN.
+	 */
+	uint32_t next_mid_ordered;
+	uint32_t next_mid_unordered;
 	uint16_t stream_no;
 	uint8_t last_msg_incomplete;
 	uint8_t state;
@@ -893,7 +897,6 @@ struct sctp_association {
 	uint32_t stream_scheduling_module;
 
 	uint32_t vrf_id;
-	uint32_t assoc_msg_id;
 	uint32_t cookie_preserve_req;
 	/* ASCONF next seq I am sending out, inits at init-tsn */
 	uint32_t asconf_seq_out;
diff --git a/sys/netinet/sctputil.c b/sys/netinet/sctputil.c
index cc18d9f05198..3f6ec551d480 100644
--- a/sys/netinet/sctputil.c
+++ b/sys/netinet/sctputil.c
@@ -1123,7 +1123,8 @@ sctp_init_asoc(struct sctp_inpcb *inp, struct sctp_tcb *stcb,
 		 * that were dropped must be notified to the upper layer as
 		 * failed to send.
 		 */
-		asoc->strmout[i].next_sequence_send = 0x0;
+		asoc->strmout[i].next_mid_ordered = 0;
+		asoc->strmout[i].next_mid_unordered = 0;
 		TAILQ_INIT(&asoc->strmout[i].outqueue);
 		asoc->strmout[i].chunks_on_queues = 0;
 #if defined(SCTP_DETAILED_STR_STATS)
@@ -4836,10 +4837,22 @@ sctp_release_pr_sctp_chunk(struct sctp_tcb *stcb, struct sctp_tmit_chunk *tp1,
 					goto oh_well;
 				}
 				memset(chk, 0, sizeof(*chk));
-				chk->rec.data.rcv_flags = SCTP_DATA_LAST_FRAG;
+				chk->rec.data.rcv_flags = 0;
 				chk->sent = SCTP_FORWARD_TSN_SKIP;
 				chk->asoc = &stcb->asoc;
-				chk->rec.data.stream_seq = strq->next_sequence_send;
+				if (stcb->asoc.idata_supported == 0) {
+					if (sp->sinfo_flags & SCTP_UNORDERED) {
+						chk->rec.data.stream_seq = 0;
+					} else {
+						chk->rec.data.stream_seq = strq->next_mid_ordered;
+					}
+				} else {
+					if (sp->sinfo_flags & SCTP_UNORDERED) {
+						chk->rec.data.stream_seq = strq->next_mid_unordered;
+					} else {
+						chk->rec.data.stream_seq = strq->next_mid_ordered;
+					}
+				}
 				chk->rec.data.stream_number = sp->stream;
 				chk->rec.data.payloadtype = sp->ppid;
 				chk->rec.data.context = sp->context;
@@ -4850,10 +4863,19 @@ sctp_release_pr_sctp_chunk(struct sctp_tcb *stcb, struct sctp_tmit_chunk *tp1,
 				TAILQ_INSERT_TAIL(&stcb->asoc.sent_queue, chk, sctp_next);
 				stcb->asoc.sent_queue_cnt++;
 				stcb->asoc.pr_sctp_cnt++;
-			} else {
-				chk->rec.data.rcv_flags |= SCTP_DATA_LAST_FRAG;
 			}
-			strq->next_sequence_send++;
+			chk->rec.data.rcv_flags |= SCTP_DATA_LAST_FRAG;
+			if (stcb->asoc.idata_supported == 0) {
+				if ((sp->sinfo_flags & SCTP_UNORDERED) == 0) {
+					strq->next_mid_ordered++;
+				}
+			} else {
+				if (sp->sinfo_flags & SCTP_UNORDERED) {
+					strq->next_mid_unordered++;
+				} else {
+					strq->next_mid_ordered++;
+				}
+			}
 	oh_well:
 			if (sp->data) {
 				/*