From 872b86da3bbfb50693d5539b1565d76f2de07039 Mon Sep 17 00:00:00 2001
From: Raja Subramanian <raja.gobi@tutanota.com>
Date: Sun, 30 Jul 2023 12:24:58 +0530
Subject: [PATCH] Delay retransmission after first send. (#1918)

* Delay retransmission after first send.

* test tweak

* english
---
 pkg/sfu/sequencer.go      |  9 +++++++--
 pkg/sfu/sequencer_test.go | 15 +++++++++++++--
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/pkg/sfu/sequencer.go b/pkg/sfu/sequencer.go
index e0f89d2c7..a2699427b 100644
--- a/pkg/sfu/sequencer.go
+++ b/pkg/sfu/sequencer.go
@@ -133,6 +133,7 @@ func (s *sequencer) push(
 		layer:       layer,
 		codecBytes:  append([]byte{}, codecBytes...),
 		ddBytes:     append([]byte{}, ddBytes...),
+		lastNack:    s.getRefTime(), // delay retransmissions after the original transmission
 	}
 
 	s.seq[slot] = &s.meta[s.metaWritePtr]
@@ -198,7 +199,7 @@ func (s *sequencer) getPacketsMeta(seqNo []uint16) []packetMeta {
 	defer s.Unlock()
 
 	meta := make([]packetMeta, 0, len(seqNo))
-	refTime := uint32(time.Now().UnixNano()/1e6 - s.startTime)
+	refTime := s.getRefTime()
 	for _, sn := range seqNo {
 		diff := s.headSN - sn
 		if diff > (1<<15) || int(diff) >= s.max {
@@ -212,7 +213,7 @@ func (s *sequencer) getPacketsMeta(seqNo []uint16) []packetMeta {
 			continue
 		}
 
-		if (seq.lastNack == 0 || refTime-seq.lastNack > uint32(math.Min(float64(ignoreRetransmission), float64(2*s.rtt)))) && seq.nacked < maxAck {
+		if refTime-seq.lastNack > uint32(math.Min(float64(ignoreRetransmission), float64(2*s.rtt))) && seq.nacked < maxAck {
 			seq.nacked++
 			seq.lastNack = refTime
 
@@ -237,3 +238,7 @@ func (s *sequencer) wrap(slot int) int {
 
 	return slot
 }
+
+func (s *sequencer) getRefTime() uint32 {
+	return uint32(time.Now().UnixNano()/1e6 - s.startTime)
+}
diff --git a/pkg/sfu/sequencer_test.go b/pkg/sfu/sequencer_test.go
index a2303742d..8fde0d9e6 100644
--- a/pkg/sfu/sequencer_test.go
+++ b/pkg/sfu/sequencer_test.go
@@ -35,9 +35,13 @@ func Test_sequencer(t *testing.T) {
 	seq.push(519, 519+off, 123, false, 2, nil, nil)
 	seq.push(518, 518+off, 123, true, 2, nil, nil)
 
-	time.Sleep(60 * time.Millisecond)
 	req := []uint16{57, 58, 62, 63, 513, 514, 515, 516, 517}
 	res := seq.getPacketsMeta(req)
+	// nothing should be returned as not enough time has elapsed since sending packet
+	require.Equal(t, 0, len(res))
+
+	time.Sleep((ignoreRetransmission + 10) * time.Millisecond)
+	res = seq.getPacketsMeta(req)
 	require.Equal(t, len(req), len(res))
 	for i, val := range res {
 		require.Equal(t, val.targetSeqNo, req[i])
@@ -46,7 +50,7 @@ func Test_sequencer(t *testing.T) {
 	}
 	res = seq.getPacketsMeta(req)
 	require.Equal(t, 0, len(res))
-	time.Sleep(150 * time.Millisecond)
+	time.Sleep((ignoreRetransmission + 10) * time.Millisecond)
 	res = seq.getPacketsMeta(req)
 	require.Equal(t, len(req), len(res))
 	for i, val := range res {
@@ -57,10 +61,16 @@ func Test_sequencer(t *testing.T) {
 
 	seq.push(521, 521+off, 123, true, 1, nil, nil)
 	m := seq.getPacketsMeta([]uint16{521 + off})
+	require.Equal(t, 0, len(m))
+	time.Sleep((ignoreRetransmission + 10) * time.Millisecond)
+	m = seq.getPacketsMeta([]uint16{521 + off})
 	require.Equal(t, 1, len(m))
 
 	seq.push(505, 505+off, 123, false, 1, nil, nil)
 	m = seq.getPacketsMeta([]uint16{505 + off})
+	require.Equal(t, 0, len(m))
+	time.Sleep((ignoreRetransmission + 10) * time.Millisecond)
+	m = seq.getPacketsMeta([]uint16{505 + off})
 	require.Equal(t, 1, len(m))
 }
 
@@ -121,6 +131,7 @@ func Test_sequencer_getNACKSeqNo(t *testing.T) {
 				n.pushPadding(i + tt.fields.offset)
 			}
 
+			time.Sleep((ignoreRetransmission + 10) * time.Millisecond)
 			g := n.getPacketsMeta(tt.args.seqNo)
 			var got []uint16
 			for _, sn := range g {