diff --git a/example/echo3/echo3_test.go b/example/echo3/echo3_test.go
new file mode 100755
index 0000000..0935029
--- /dev/null
+++ b/example/echo3/echo3_test.go
@@ -0,0 +1,81 @@
+// Echo test that uses slightly higher level APIs.
+
+package echo2_test
+
+import (
+	"github.com/jart/gosip/dsp"
+	"github.com/jart/gosip/rtp"
+	"github.com/jart/gosip/sdp"
+	"github.com/jart/gosip/sip"
+	"net"
+	"testing"
+	"time"
+)
+
+func TestCallToEchoApp(t *testing.T) {
+	invite := &sip.Msg{
+		Request: &sip.URI{User: "echo", Host: "127.0.0.1", Port: 5060},
+	}
+
+	// Create RTP audio session.
+	rs, err := rtp.NewSession("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer rs.Sock.Close()
+	rtpaddr := rs.Sock.LocalAddr().(*net.UDPAddr)
+	sip.AttachSDP(invite, sdp.New(rtpaddr, sdp.ULAWCodec, sdp.DTMFCodec))
+
+	// Create a SIP phone call.
+	dl, err := sip.NewDialog(invite)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We're going to send white noise every 20ms.
+	var frame rtp.Frame
+	awgn := dsp.NewAWGN(-45.0)
+	ticker := time.NewTicker(20 * time.Millisecond)
+	defer ticker.Stop()
+
+	// Hangup after 200ms.
+	death := time.After(200 * time.Millisecond)
+
+	// Let's GO!
+	var answered bool
+	for {
+		select {
+		case err := <-rs.E:
+			t.Error("RTP recv failed:", err)
+			dl.Hangup <- true
+		case <-rs.C:
+			// Do nothing with received audio.
+		case <-ticker.C:
+			for n := 0; n < 160; n++ {
+				frame[n] = awgn.Get()
+			}
+			if err := rs.Send(&frame); err != nil {
+				t.Fatal("RTP send failed:", err)
+			}
+		case <-dl.OnErr:
+			t.Error(err)
+			return
+		case state := <-dl.OnState:
+			switch state {
+			case sip.DialogAnswered:
+				answered = true
+			case sip.DialogHangup:
+				return
+			}
+		case ms := <-dl.OnSDP:
+			rs.Peer = &net.UDPAddr{IP: net.ParseIP(ms.Addr), Port: int(ms.Audio.Port)}
+		case <-death:
+			dl.Hangup <- true
+		}
+	}
+
+	// The dialog has shut down cleanly. Was it answered?
+	if !answered {
+		t.Error("Call didn't get answered!")
+	}
+}
diff --git a/rtp/session.go b/rtp/session.go
index 7a8f808..175ff69 100644
--- a/rtp/session.go
+++ b/rtp/session.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"github.com/jart/gosip/dsp"
 	"github.com/jart/gosip/sdp"
+	"log"
 	"math/rand"
 	"net"
 	"strconv"
@@ -128,11 +129,10 @@ func listenRTP(host string) (sock net.PacketConn, err error) {
 		port := rtpBindPortMin + rand.Int63()%(rtpBindPortMax-rtpBindPortMin+1)
 		saddr := net.JoinHostPort(host, strconv.FormatInt(port, 10))
 		sock, err = net.ListenPacket("udp", saddr)
-		if err != nil {
-			if !strings.Contains(err.Error(), "address already in use") {
-				break
-			}
+		if err == nil || !strings.Contains(err.Error(), "address already in use") {
+			break
 		}
+		log.Println("RTP listen congestion:", saddr)
 	}
 	return
 }
diff --git a/sip/dialog.go b/sip/dialog.go
new file mode 100755
index 0000000..0460f13
--- /dev/null
+++ b/sip/dialog.go
@@ -0,0 +1,266 @@
+// SIP Transport Layer.  Responsible for serializing messages to/from
+// your network.
+
+package sip
+
+import (
+	"bytes"
+	"errors"
+	"github.com/jart/gosip/sdp"
+	"github.com/jart/gosip/util"
+	"log"
+	"net"
+	"time"
+)
+
+const (
+	DialogConnected = 1
+	DialogRinging   = 2
+	DialogAnswered  = 3
+	DialogHangup    = 4
+	resendInterval  = 200 * time.Millisecond
+	maxResends      = 2
+)
+
+// Dialog represents an outbound phone call.
+type Dialog struct {
+	OnErr   <-chan error
+	OnState <-chan int
+	OnSDP   <-chan *sdp.SDP
+	Hangup  chan<- bool
+}
+
+type dialogState struct {
+	sock         *net.UDPConn
+	sockMsgs     <-chan *Msg
+	sockErrs     <-chan error
+	errChan      chan<- error
+	sdpChan      chan<- *sdp.SDP
+	stateChan    chan<- int
+	doHangupChan <-chan bool
+	routes       *AddressRoute
+	invite       *Msg
+	response     *Msg
+	resend       *Msg
+	resends      int
+	timer        <-chan time.Time
+}
+
+// NewDialog creates a phone call.
+func NewDialog(invite *Msg) (dl *Dialog, err error) {
+	invite, host, port, err := RouteMessage(nil, nil, invite)
+	if err != nil {
+		return nil, err
+	}
+	routes, err := RouteAddress(host, port)
+	if err != nil {
+		return nil, err
+	}
+	errChan := make(chan error)
+	sdpChan := make(chan *sdp.SDP)
+	stateChan := make(chan int)
+	doHangupChan := make(chan bool, 4)
+	dls := &dialogState{
+		errChan:      errChan,
+		sdpChan:      sdpChan,
+		stateChan:    stateChan,
+		doHangupChan: doHangupChan,
+		invite:       invite,
+		routes:       routes,
+	}
+	go dls.run()
+	return &Dialog{
+		OnErr:   errChan,
+		OnState: stateChan,
+		OnSDP:   sdpChan,
+		Hangup:  doHangupChan,
+	}, nil
+}
+
+func (dls *dialogState) popRoute() bool {
+	if dls.routes == nil {
+		dls.errChan <- errors.New("failed to contact host")
+		return false
+	}
+	dls.cleanup()
+	conn, err := net.Dial("udp", dls.routes.Address)
+	dls.routes = dls.routes.Next
+	if err != nil {
+		log.Println("net.Dial() failed:", err)
+		return dls.popRoute()
+	}
+	dls.sock = conn.(*net.UDPConn)
+	laddr := conn.LocalAddr().(*net.UDPAddr)
+	lhost := laddr.IP.String()
+	lport := uint16(laddr.Port)
+	dls.invite.Via = &Via{
+		Host:   lhost,
+		Port:   lport,
+		Params: Params{"branch": util.GenerateBranch()},
+	}
+	dls.invite.Contact = &Addr{
+		Uri: &URI{
+			Scheme: "sip",
+			Host:   lhost,
+			Port:   lport,
+			Params: Params{"transport": "udp"},
+		},
+	}
+	PopulateMessage(nil, nil, dls.invite)
+	dls.resend = dls.invite
+	dls.timer = time.After(resendInterval)
+	dls.resends = 0
+	sockMsgs := make(chan *Msg)
+	sockErrs := make(chan error)
+	dls.sockMsgs = sockMsgs
+	dls.sockErrs = sockErrs
+	go ReceiveMessages(dls.invite.Contact, dls.sock, sockMsgs, sockErrs)
+	return dls.send(dls.resend)
+}
+
+func (dls *dialogState) run() {
+	defer dls.sabotage()
+	defer dls.cleanup()
+	if !dls.popRoute() {
+		return
+	}
+	for {
+		select {
+		case err := <-dls.sockErrs:
+			if util.IsRefused(err) {
+				if !dls.popRoute() {
+					return
+				}
+			} else {
+				dls.errChan <- err
+				return
+			}
+		case <-dls.timer:
+			if dls.resends < maxResends {
+				if !dls.send(dls.resend) {
+					return
+				}
+				dls.resends++
+				dls.timer = time.After(resendInterval)
+			} else {
+				if !dls.popRoute() {
+					return
+				}
+			}
+		case <-dls.doHangupChan:
+			if !dls.hangup() {
+				return
+			}
+		case msg := <-dls.sockMsgs:
+			if msg.CallID != dls.invite.CallID {
+				continue
+			}
+			if msg.IsResponse {
+				if msg.Status >= StatusOK && msg.CSeq == dls.invite.CSeq {
+					if msg.Contact != nil {
+						if !dls.send(NewAck(dls.invite, msg)) {
+							return
+						}
+					}
+					if msg.Status > StatusOK {
+						dls.errChan <- errors.New(msg.Phrase)
+						return
+					}
+				}
+				switch msg.Status {
+				case StatusTrying:
+					dls.routes = nil
+					dls.timer = nil
+					dls.stateChan <- DialogConnected
+				case StatusRinging, StatusSessionProgress:
+					dls.stateChan <- DialogRinging
+				case StatusOK:
+					switch msg.CSeqMethod {
+					case dls.invite.Method:
+						if dls.response == nil {
+							dls.stateChan <- DialogAnswered
+						}
+						dls.response = msg
+					case MethodBye, MethodCancel:
+						dls.stateChan <- DialogHangup
+						return
+					default:
+						dls.errChan <- errors.New("Bad CSeq Method")
+						return
+					}
+				}
+				if msg.Headers["Content-Type"] == sdp.ContentType {
+					ms, err := sdp.Parse(msg.Payload)
+					if err != nil {
+						log.Println("Bad SDP payload:", err)
+					} else {
+						dls.sdpChan <- ms
+					}
+				}
+			} else {
+				if msg.MaxForwards <= 0 {
+					if !dls.send(NewResponse(msg, StatusTooManyHops)) {
+						return
+					}
+					dls.errChan <- errors.New("Froot loop detected")
+					return
+				}
+				switch msg.Method {
+				case MethodBye:
+					if !dls.send(NewResponse(msg, StatusOK)) {
+						return
+					}
+					dls.stateChan <- DialogHangup
+					return
+				}
+			}
+		}
+	}
+}
+
+func (dls *dialogState) send(msg *Msg) bool {
+	// TODO(jart): Double-check route matches socket binding.
+	if msg.MaxForwards > 0 {
+		msg.MaxForwards--
+	}
+	ts := time.Now()
+	addTimestamp(msg, ts)
+	var b bytes.Buffer
+	msg.Append(&b)
+	if *tracing {
+		trace("send", b.String(), dls.sock.RemoteAddr(), ts)
+	}
+	_, err := dls.sock.Write(b.Bytes())
+	if err != nil {
+		dls.errChan <- err
+		return false
+	}
+	return true
+}
+
+func (dls *dialogState) hangup() bool {
+	if dls.response != nil {
+		dls.resend = NewBye(dls.invite, dls.response)
+	} else {
+		dls.resend = NewCancel(dls.invite)
+	}
+	if !dls.send(dls.resend) {
+		return false
+	}
+	dls.resends = 0
+	dls.timer = time.After(resendInterval)
+	return true
+}
+
+func (dls *dialogState) cleanup() {
+	if dls.sock != nil {
+		dls.sock.Close()
+		dls.sock = nil
+	}
+}
+
+func (dls *dialogState) sabotage() {
+	close(dls.errChan)
+	close(dls.sdpChan)
+	close(dls.stateChan)
+}
diff --git a/sip/messages.go b/sip/messages.go
index 2c488cb..aaf3368 100644
--- a/sip/messages.go
+++ b/sip/messages.go
@@ -111,6 +111,9 @@ func AckMatch(msg, ack *Msg) bool {
 }
 
 func AttachSDP(msg *Msg, ms *sdp.SDP) {
+	if msg.Headers == nil {
+		msg.Headers = Headers{}
+	}
 	msg.Headers["Content-Type"] = sdp.ContentType
 	msg.Payload = ms.String()
 }
diff --git a/sip/msg.go b/sip/msg.go
index d7992bf..17d9ddb 100755
--- a/sip/msg.go
+++ b/sip/msg.go
@@ -378,25 +378,35 @@ func (msg *Msg) Append(b *bytes.Buffer) error {
 	return nil
 }
 
-func (msg *Msg) parseFirstLine(s string) (err error) {
-	toks := strings.Split(s, " ")
-	if toks != nil && len(toks) == 3 && toks[2] == "SIP/2.0" {
-		msg.Phrase = ""
-		msg.Status = 0
-		msg.Method = toks[0]
-		msg.Request = new(URI)
-		msg.Request, err = ParseURI(toks[1])
-	} else if toks != nil && len(toks) == 3 && toks[0] == "SIP/2.0" {
+func (msg *Msg) parseFirstLine(s string) error {
+	i := strings.Index(s, "SIP/2.0")
+	if i == -1 {
+		return errors.New("Not a SIP message")
+	} else if i == 0 {
 		msg.IsResponse = true
-		msg.Method = ""
-		msg.Request = nil
-		msg.Phrase = toks[2]
-		msg.Status, err = strconv.Atoi(toks[1])
+		toks := strings.SplitN(s, " ", 3)
+		if len(toks) < 2 {
+			return errors.New("Bad response status line")
+		}
+		s, err := strconv.Atoi(toks[1])
 		if err != nil {
-			return errors.New("Invalid status")
+			return errors.New("Bad response status code")
+		}
+		msg.Status = s
+		if len(toks) == 3 {
+			msg.Phrase = toks[2]
+		} else {
+			msg.Phrase = Phrase(msg.Status)
 		}
 	} else {
-		err = errors.New("Bad protocol or request line")
+		j := strings.Index(s, " ")
+		msg.Method = s[:j]
+		msg.Request = new(URI)
+		r, err := ParseURI(s[j+1 : i-1])
+		msg.Request = r
+		if err != nil {
+			return err
+		}
 	}
-	return err
+	return nil
 }
diff --git a/sip/route.go b/sip/route.go
index e75d7c2..b0966a3 100644
--- a/sip/route.go
+++ b/sip/route.go
@@ -2,6 +2,7 @@ package sip
 
 import (
 	"errors"
+	"github.com/jart/gosip/util"
 	"log"
 	"net"
 )
@@ -11,12 +12,52 @@ type AddressRoute struct {
 	Next    *AddressRoute
 }
 
+func PopulateMessage(via *Via, contact *Addr, msg *Msg) {
+	if !msg.IsResponse {
+		if msg.Method == "" {
+			msg.Method = "INVITE"
+		}
+		if msg.Via == nil {
+			msg.Via = via
+		}
+		if msg.Contact == nil {
+			msg.Contact = contact
+		}
+		if msg.To == nil {
+			msg.To = &Addr{Uri: msg.Request}
+		}
+		if msg.From == nil {
+			msg.From = msg.Contact
+		}
+		if msg.CallID == "" {
+			msg.CallID = util.GenerateCallID()
+		}
+		if msg.CSeq == 0 {
+			msg.CSeq = util.GenerateCSeq()
+		}
+		if msg.CSeqMethod == "" {
+			msg.CSeqMethod = msg.Method
+		}
+		if msg.MaxForwards == 0 {
+			msg.MaxForwards = 70
+		}
+		if _, ok := msg.Via.Params["branch"]; !ok {
+			msg.Via = msg.Via.Copy()
+			msg.Via.Params["branch"] = util.GenerateBranch()
+		}
+		if _, ok := msg.From.Params["tag"]; !ok {
+			msg.From = msg.From.Copy()
+			msg.From.Params["tag"] = util.GenerateTag()
+		}
+		if _, ok := msg.Headers["User-Agent"]; !ok {
+			msg.Headers["User-Agent"] = GosipUserAgent
+		}
+	}
+}
+
 func RouteMessage(via *Via, contact *Addr, old *Msg) (msg *Msg, host string, port uint16, err error) {
 	msg = new(Msg)
 	*msg = *old // Start off with a shallow copy.
-	if msg.Contact == nil {
-		msg.Contact = contact
-	}
 	if msg.IsResponse {
 		if via.CompareHostPort(msg.Via) {
 			msg.Via = msg.Via.Next
@@ -61,12 +102,15 @@ func RouteAddress(host string, port uint16) (routes *AddressRoute, err error) {
 	if port == 0 {
 		_, srvs, err := net.LookupSRV("sip", "udp", host)
 		if err == nil && len(srvs) > 0 {
+			s := ""
 			for i := len(srvs) - 1; i >= 0; i-- {
 				routes = &AddressRoute{
 					Address: net.JoinHostPort(srvs[i].Target, portstr(srvs[i].Port)),
 					Next:    routes,
 				}
+				s = " " + routes.Address + s
 			}
+			log.Printf("%s routes to: %s", host, s)
 			return routes, nil
 		}
 		log.Println("net.LookupSRV(sip, udp, %s) failed: %s", err)
diff --git a/sip/trace.go b/sip/trace.go
index 94349e8..57fce96 100644
--- a/sip/trace.go
+++ b/sip/trace.go
@@ -17,7 +17,7 @@ func trace(dir, pkt string, addr net.Addr, t time.Time) {
 	size := len(pkt)
 	bar := strings.Repeat("-", 72)
 	suffix := "\n"
-	if pkt[len(pkt)-1] == '\n' {
+	if pkt != "" && pkt[len(pkt)-1] == '\n' {
 		suffix = ""
 	}
 	log.Printf(
diff --git a/sip/transport.go b/sip/transport.go
index bcf3f75..40cf50c 100755
--- a/sip/transport.go
+++ b/sip/transport.go
@@ -66,6 +66,7 @@ func NewTransport(contact *Addr) (tp *Transport, err error) {
 
 // Sends a SIP message.
 func (tp *Transport) Send(msg *Msg) error {
+	PopulateMessage(tp.Via, tp.Contact, msg)
 	msg, host, port, err := RouteMessage(tp.Via, tp.Contact, msg)
 	if err != nil {
 		return err