diff --git a/examples/stack/main.go b/examples/stack/main.go
index fcf4d5e..63b2a49 100644
--- a/examples/stack/main.go
+++ b/examples/stack/main.go
@@ -17,7 +17,6 @@ func main() {
 	rng := rand.New(rand.NewSource(1))
 	var gen ltesto.PacketGen
 	gen.RandomizeAddrs(rng)
-
 	slogger := logger{slog.Default()}
 	lStack := LinkStack{
 		logger: slogger,
@@ -49,18 +48,29 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-
-	err = pStack.tcb.Open(tcp.Value(rng.Int()), 256, tcp.StateListen)
+	iss := tcp.Value(100)
+	err = pStack.tcb.Open(iss, 256, tcp.StateListen)
 	if err != nil {
 		log.Fatal(err)
 	}
-
+	seg := tcp.Segment{
+		SEQ:     300,
+		ACK:     iss,
+		DATALEN: 0,
+		WND:     256,
+		Flags:   tcp.FlagSYN,
+	}
 	buf := make([]byte, lStack.mtu)
-	packet := gen.AppendRandomIPv4TCPPacket(buf[:0], rng)
+	packet := gen.AppendRandomIPv4TCPPacket(buf[:0], rng, seg)
 	err = lStack.RecvEth(packet)
 	if err != nil {
 		log.Fatal(err)
 	}
+	n, err := lStack.HandleEth(buf)
+	if err != nil {
+		log.Fatal(n, err)
+	}
+	log.Println("success receiving packet")
 }
 
 type Handler interface {
@@ -334,7 +344,7 @@ func (ts *TCPStack) Handle(ipFrame []byte, tcpOff int) (n int, err error) {
 		return 0, err
 	}
 	// TCP packet written.
-	tfrm, _ := lneto.NewTCPFrame(ipFrame[tcpOff:])
+	tfrm, _ := lneto.NewTCPFrame(ipFrame[tcpOff : tcpOff+n])
 	ts.validator.ResetErr()
 	tfrm.ValidateSize(&ts.validator) // Perform basic validation.
 	if err = ts.validator.Err(); err != nil {
diff --git a/frames.go b/frames.go
index 95c13e8..c32c02f 100644
--- a/frames.go
+++ b/frames.go
@@ -610,7 +610,7 @@ func (tfrm TCPFrame) CalculateIPv4CRC(ifrm IPv4Frame) uint16 {
 	ifrm.crcWriteTCPPseudo(&crc)
 	expectLen := int(ifrm.TotalLength()) - ifrm.HeaderLength()
 	if expectLen != len(tfrm.buf) {
-		println("unexpected TCP buffer length mismatches IPv4 header total length", expectLen, len(tfrm.buf))
+		println("unexpected TCP buffer length mismatches IPv4 header total length", len(tfrm.buf), expectLen)
 	}
 	tfrm.crcWrite(&crc)
 	return crc.Sum16()
@@ -622,7 +622,7 @@ func (tfrm TCPFrame) CalculateIPv6CRC(ifrm IPv6Frame) uint16 {
 	ifrm.crcWritePseudo(&crc)
 	expectLen := int(ifrm.PayloadLength())
 	if expectLen != len(tfrm.buf) {
-		println("unexpected TCP buffer length mismatches IPv4 header total length", expectLen, len(tfrm.buf))
+		println("unexpected TCP buffer length mismatches IPv4 header total length", len(tfrm.buf), expectLen)
 	}
 	tfrm.crcWrite(&crc)
 	return crc.Sum16()
diff --git a/internal/ltesto/ltesto.go b/internal/ltesto/ltesto.go
index 947e68b..a21e9a1 100644
--- a/internal/ltesto/ltesto.go
+++ b/internal/ltesto/ltesto.go
@@ -2,6 +2,7 @@ package ltesto
 
 import (
 	"bytes"
+	"math"
 	"math/rand"
 
 	"github.com/soypat/lneto"
@@ -34,13 +35,17 @@ func (gen *PacketGen) RandomizeAddrs(rng *rand.Rand) {
 	gen.DstTCP = uint16(ports >> 16)
 }
 
-func (gen *PacketGen) AppendRandomIPv4TCPPacket(dst []byte, rng *rand.Rand) []byte {
+func (gen *PacketGen) AppendRandomIPv4TCPPacket(dst []byte, rng *rand.Rand, seg tcp.Segment) []byte {
+	if seg.WND > math.MaxUint16 {
+		panic("TCP segment window overflow")
+	} else if seg.DATALEN > 2048 {
+		panic("too long datalen")
+	}
 	ri := rng.Int()
 	var (
-		isVLAN     = ri&(1<<0) != 0
-		hasIPOpt   = ri&(1<<1) != 0
-		hasTCPOpt  = ri&(1<<2) != 0
-		hasPayload = ri&(1<<3) != 0
+		isVLAN    = ri&(1<<0) != 0
+		hasIPOpt  = ri&(1<<1) != 0
+		hasTCPOpt = ri&(1<<2) != 0
 	)
 	var etherType lneto.EtherType = lneto.EtherTypeIPv4
 	var ipOpts []byte
@@ -56,14 +61,11 @@ func (gen *PacketGen) AppendRandomIPv4TCPPacket(dst []byte, rng *rand.Rand) []by
 	if hasTCPOpt {
 		tcpOpts = []byte{byte(tcp.OptSACKPermitted), 0, 1, 0}
 	}
-	var payloadLen int
-	if hasPayload {
-		payloadLen = (ri >> 16) % 1024
-	}
+
 	ipOptWLen := sizeWord(len(ipOpts))
 	tcpOptWlen := sizeWord(len(tcpOpts))
 	off := len(dst)
-	dst = append(dst, make([]byte, ethsize+sizeHeaderIPv4+4*int(ipOptWLen)+sizeHeaderTCP+4*int(tcpOptWlen)+payloadLen)...)
+	dst = append(dst, make([]byte, ethsize+sizeHeaderIPv4+4*int(ipOptWLen)+sizeHeaderTCP+4*int(tcpOptWlen)+int(seg.DATALEN))...)
 	efrm, err := lneto.NewEthFrame(dst[off:])
 	if err != nil {
 		panic(err)
@@ -99,11 +101,11 @@ func (gen *PacketGen) AppendRandomIPv4TCPPacket(dst []byte, rng *rand.Rand) []by
 	}
 	tfrm.SetSourcePort(gen.SrcTCP)
 	tfrm.SetDestinationPort(gen.DstTCP)
-	tfrm.SetSeq(tcp.Value(rng.Uint32()))
-	tfrm.SetAck(tcp.Value(rng.Uint32()))
+	tfrm.SetSeq(seg.SEQ)
+	tfrm.SetAck(seg.ACK)
 	wlen := sizeWord(sizeHeaderTCP + len(tcpOpts))
-	tfrm.SetOffsetAndFlags(wlen, tcp.Flags(rng.Uint32()))
-	tfrm.SetWindowSize(uint16(rng.Uint32()))
+	tfrm.SetOffsetAndFlags(wlen, seg.Flags)
+	tfrm.SetWindowSize(uint16(seg.WND))
 	urgPtr := uint16(rng.Uint32())
 	tfrm.SetUrgentPtr(urgPtr)
 	tcpPayload := tfrm.Payload()
@@ -111,6 +113,9 @@ func (gen *PacketGen) AppendRandomIPv4TCPPacket(dst []byte, rng *rand.Rand) []by
 	if len(tcpPayload) > 0 {
 		rng.Read(tcpPayload)
 		firstPayloadByte = tcpPayload[0]
+		if len(tcpPayload) != int(seg.DATALEN) {
+			panic("incorrect payload length calculation")
+		}
 	}
 	// Set Variable section of data.
 	copy(ifrm.Options(), ipOpts)