diff --git a/serialstream.go b/serialstream.go
index 837a59f..4c2819b 100644
--- a/serialstream.go
+++ b/serialstream.go
@@ -2,12 +2,14 @@ package main
 
 import (
 	"bytes"
+	"encoding/binary"
 	"time"
 
 	"github.com/nonoo/kappanhang/log"
 )
 
 const maxSerialFrameLength = 80 // Max. frame length according to Hamlib.
+const serialRxSeqBufLength = 100 * time.Millisecond
 
 type serialStream struct {
 	common streamCommon
@@ -17,6 +19,13 @@ type serialStream struct {
 
 	sendSeq uint16
 
+	lastSeqBufFrontRxSeq uint16
+	rxSeqBuf             seqBuf
+	rxSeqBufEntryChan    chan seqBufEntry
+
+	receivedSerialData bool
+	lastReceivedSeq    uint16
+
 	readFromSerialPort struct {
 		buf          bytes.Buffer
 		frameStarted bool
@@ -67,20 +76,85 @@ func (s *serialStream) sendOpenClose(close bool) error {
 	return nil
 }
 
-func (s *serialStream) handleRead(r []byte) {
-	if len(r) >= 22 {
-		if r[16] == 0xc1 && r[0]-0x15 == r[17] {
-			r = r[21:]
+func (s *serialStream) handleRxSeqBufEntry(e seqBufEntry) {
+	gotSeq := uint16(e.seq)
+	if s.receivedSerialData {
+		expectedSeq := s.lastReceivedSeq + 1
+		if expectedSeq != gotSeq {
+			var missingPkts int
+			if gotSeq > expectedSeq {
+				missingPkts = int(gotSeq) - int(expectedSeq)
+			} else {
+				missingPkts = int(gotSeq) + 65536 - int(expectedSeq)
+			}
+			log.Error("lost ", missingPkts, " packets")
+		}
+	}
+	s.lastReceivedSeq = gotSeq
+	s.receivedSerialData = true
 
-			// log.Print("fromradio ", r)
+	if len(e.data) == 16 { // Do not send pkt0s.
+		return
+	}
 
-			s.serialPort.write <- r
-			if s.tcpsrv.toClient != nil {
-				s.tcpsrv.toClient <- r
+	e.data = e.data[21:]
+
+	s.serialPort.write <- e.data
+	if s.tcpsrv.toClient != nil {
+		s.tcpsrv.toClient <- e.data
+	}
+}
+
+func (s *serialStream) requestRetransmitIfNeeded(gotSeq uint16) error {
+	prevExpectedSeq := gotSeq - 1
+	if s.lastSeqBufFrontRxSeq != prevExpectedSeq {
+		var missingPkts int
+		var sr seqNumRange
+		if prevExpectedSeq > s.lastSeqBufFrontRxSeq {
+			sr[0] = s.lastSeqBufFrontRxSeq
+			sr[1] = prevExpectedSeq
+			missingPkts = int(prevExpectedSeq) - int(s.lastSeqBufFrontRxSeq)
+		} else {
+			sr[0] = prevExpectedSeq
+			sr[1] = s.lastSeqBufFrontRxSeq
+			missingPkts = int(prevExpectedSeq) + 65536 - int(s.lastSeqBufFrontRxSeq)
+		}
+		if missingPkts == 1 {
+			log.Debug("request pkt #", sr[1], " retransmit")
+			if err := s.common.sendRetransmitRequest(sr[1]); err != nil {
+				return err
+			}
+		} else if missingPkts < 50 {
+			log.Debug("request pkt #", sr[0], "-#", sr[1], " retransmit")
+			if err := s.common.sendRetransmitRequestForRanges([]seqNumRange{sr}); err != nil {
+				return err
 			}
 		}
 	}
+	s.lastSeqBufFrontRxSeq = gotSeq
+	return nil
+}
 
+func (s *serialStream) handleSerialPacket(r []byte) error {
+	gotSeq := binary.LittleEndian.Uint16(r[6:8])
+	addedToFront, _ := s.rxSeqBuf.add(seqNum(gotSeq), r)
+
+	// If the packet is not added to the front of the seqbuf, then it means that it was an answer for a
+	// retransmit request (or it was an out of order packet which we don't want start a retransmit).
+	if !addedToFront {
+		return nil
+	}
+
+	return s.requestRetransmitIfNeeded(gotSeq)
+}
+
+func (s *serialStream) handleRead(r []byte) error {
+	// We add both serial data and pkt0 to the seqbuf.
+	if (len(r) == 16 && bytes.Equal(r[:6], []byte{0x10, 0x00, 0x00, 0x00, 0x00, 0x00})) || // Pkt0?
+		(len(r) >= 22 && r[16] == 0xc1 && r[0]-0x15 == r[17]) { // Serial data?
+		return s.handleSerialPacket(r)
+	}
+	return nil
 }
 
 func (s *serialStream) gotDataForRadio(r []byte) {
@@ -117,8 +191,6 @@ func (s *serialStream) gotDataForRadio(r []byte) {
 	for _, b := range r {
 		s.readFromSerialPort.buf.WriteByte(b)
 		if b == 0xfc || b == 0xfd || s.readFromSerialPort.buf.Len() == maxSerialFrameLength {
-			// log.Print("toradio ", s.readFromSerialPort.buf.Bytes())
-
 			if err := s.send(s.readFromSerialPort.buf.Bytes()); err != nil {
 				reportError(err)
 			}
@@ -136,7 +208,11 @@ func (s *serialStream) loop() {
 	for {
 		select {
 		case r := <-s.common.readChan:
-			s.handleRead(r)
+			if err := s.handleRead(r); err != nil {
+				reportError(err)
+			}
+		case e := <-s.rxSeqBufEntryChan:
+			s.handleRxSeqBufEntry(e)
 		case r := <-s.serialPort.read:
 			s.gotDataForRadio(r)
 		case r := <-s.tcpsrv.fromClient:
@@ -196,6 +272,8 @@ func (s *serialStream) init() error {
 	if err := s.common.init("serial", 50002); err != nil {
 		return err
 	}
+	s.rxSeqBufEntryChan = make(chan seqBufEntry)
+	s.rxSeqBuf.init(serialRxSeqBufLength, 0xffff, 0, s.rxSeqBufEntryChan)
 	return nil
 }
 
@@ -212,4 +290,5 @@ func (s *serialStream) deinit() {
 		<-s.deinitFinishedChan
 	}
 	s.common.deinit()
+	s.rxSeqBuf.deinit()
 }