Add support for symmetric RTP

pkg/config/config.go

@@ -102,6 +102,7 @@ type Config struct {
 
 	MediaTimeout        time.Duration   `yaml:"media_timeout"`
 	MediaTimeoutInitial time.Duration   `yaml:"media_timeout_initial"`
+	SymmetricRTP        bool            `yaml:"symmetric_rtp"`
 	Codecs              map[string]bool `yaml:"codecs"`
 
 	// HideInboundPort controls how SIP endpoint responds to unverified inbound requests.

pkg/sip/inbound.go

@@ -980,6 +980,7 @@ func (c *inboundCall) runMediaConn(tid traceid.ID, offerData []byte, enc livekit
 		Ports:               conf.RTPPort,
 		MediaTimeoutInitial: c.s.conf.MediaTimeoutInitial,
 		MediaTimeout:        c.s.conf.MediaTimeout,
+		SymmetricRTP:        conf.SymmetricRTP,
 		EnableJitterBuffer:  c.jitterBuf,
 		LogSignalChanges:    logSignalChanges,
 		Stats:               &c.stats.Port,

pkg/sip/media_port.go

@@ -190,15 +190,16 @@ type UDPConn interface {
 	WriteToUDPAddrPort(b []byte, addr netip.AddrPort) (int, error)
 }
 
-func newUDPConn(log logger.Logger, conn UDPConn) *udpConn {
-	return &udpConn{UDPConn: conn, log: log, stopped: make(chan struct{})}
+func newUDPConn(log logger.Logger, conn UDPConn, symmetricRTP bool) *udpConn {
+	return &udpConn{UDPConn: conn, log: log, stopped: make(chan struct{}), symmetricRTP: symmetricRTP}
 }
 
 type udpConn struct {
 	UDPConn
 	stopping core.Fuse
 	stopped  chan struct{}
 	log      logger.Logger
+	symmetricRTP bool
 	src      atomic.Pointer[netip.AddrPort]
 	dst      atomic.Pointer[netip.AddrPort]
 }
@@ -231,6 +232,12 @@ func (c *udpConn) Read(b []byte) (n int, err error) {
 	} else if *prev != addr {
 		c.log.Infow("changing media source", "addr", addr.String())
 	}
+	if c.symmetricRTP {
+		dst := c.dst.Load()
+		if dst == nil || !dst.IsValid() || *dst != addr {
+			c.SetDst(addr)
+		}
+	}
 	return n, err
 }
 
@@ -289,6 +296,7 @@ type MediaOptions struct {
 	Ports               rtcconfig.PortRange
 	MediaTimeoutInitial time.Duration
 	MediaTimeout        time.Duration
+	SymmetricRTP        bool
 	Stats               *PortStats
 	EnableJitterBuffer  bool
 	NoInputResample     bool
@@ -335,7 +343,7 @@ func NewMediaPortWith(tid traceid.ID, log logger.Logger, mon *stats.CallMonitor,
 		timeoutResetTick: make(chan time.Duration, 1),
 		jitterEnabled:    opts.EnableJitterBuffer,
 		logSignalChanges: opts.LogSignalChanges,
-		port:             newUDPConn(log, conn),
+		port:             newUDPConn(log, conn, opts.SymmetricRTP),
 		audioOut:         msdk.NewSwitchWriter(sampleRate),
 		audioIn:          msdk.NewSwitchWriter(inSampleRate),
 		stats:            opts.Stats,

pkg/sip/media_port_test.go

@@ -542,3 +542,54 @@ func TestMediaTimeout(t *testing.T) {
 		}
 	})
 }
+
+func TestSymmetricRTP(t *testing.T) {
+	t.Run("disabled", func(t *testing.T) {
+		m1, m2 := newMediaPair(t, &MediaOptions{SymmetricRTP: false}, nil)
+		dstPtr := m1.port.dst.Load()
+		require.NotNil(t, dstPtr)
+		dst := *dstPtr
+		require.True(t, dst.IsValid())
+
+		c2 := m2.port.UDPConn.(*testUDPConn)
+		newAddr := netip.AddrPortFrom(newIP("9.9.9.9"), 9999)
+		c2.addr = newAddr
+
+		err := m2.GetAudioWriter().WriteSample(msdk.PCM16Sample{0, 0})
+		require.NoError(t, err)
+
+		select {
+		case <-m1.Received():
+		case <-time.After(time.Second):
+			t.Fatal("no media received")
+		}
+
+		curDstPtr := m1.port.dst.Load()
+		require.NotNil(t, curDstPtr)
+		require.Equal(t, dst, *curDstPtr)
+	})
+
+	t.Run("enabled", func(t *testing.T) {
+		m1, m2 := newMediaPair(t, &MediaOptions{SymmetricRTP: true}, nil)
+		dstPtr := m1.port.dst.Load()
+		require.NotNil(t, dstPtr)
+		require.True(t, dstPtr.IsValid())
+
+		c2 := m2.port.UDPConn.(*testUDPConn)
+		newAddr := netip.AddrPortFrom(newIP("9.9.9.9"), 9999)
+		c2.addr = newAddr
+
+		err := m2.GetAudioWriter().WriteSample(msdk.PCM16Sample{0, 0})
+		require.NoError(t, err)
+
+		select {
+		case <-m1.Received():
+		case <-time.After(time.Second):
+			t.Fatal("no media received")
+		}
+
+		curDstPtr := m1.port.dst.Load()
+		require.NotNil(t, curDstPtr)
+		require.Equal(t, newAddr, *curDstPtr)
+	})
+}

pkg/sip/outbound.go

@@ -144,6 +144,7 @@ func (c *Client) newCall(ctx context.Context, tid traceid.ID, conf *config.Confi
 		Ports:               conf.RTPPort,
 		MediaTimeoutInitial: c.conf.MediaTimeoutInitial,
 		MediaTimeout:        c.conf.MediaTimeout,
+		SymmetricRTP:        c.conf.SymmetricRTP,
 		EnableJitterBuffer:  call.jitterBuf,
 		LogSignalChanges:    signalLoggingEnabled,
 		Stats:               &call.stats.Port,