diff --git a/README.md b/README.md
index 2c7091ae..3f0e924c 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,7 @@ The first version was sponsored by Suretec Systems Ltd. T/A [SureVoIP](http://ww
 ## Contributing
 The project is inseparable from the contributors of the community.
 - [CloudWebRTC](https://github.com/cloudwebrtc) - Original Author
+- [Robert Sutton](https://github.com/rlsutton1) - Contributor
 
 ## License
 dart-sip-ua is released under the [MIT license](https://github.com/cloudwebrtc/dart-sip-ua/blob/master/LICENSE).
diff --git a/example/analysis_options.yaml b/example/analysis_options.yaml
index d2656c3a..9aaad78c 100644
--- a/example/analysis_options.yaml
+++ b/example/analysis_options.yaml
@@ -1,27 +1,6 @@
 include: package:pedantic/analysis_options.yaml
 
 analyzer:
-  errors:
-    unused_local_variable: ignore
-    unnecessary_new: ignore
-    slash_for_doc_comments: ignore
-    library_prefixes: ignore
-    unused_field: ignore
-    top_level_function_literal_block: ignore
-    avoid_init_to_null: ignore
-    prefer_is_empty: ignore
-    unused_element: ignore
-    curly_braces_in_flow_control_structures: ignore
-    unnecessary_null_in_if_null_operators: ignore
-    prefer_contains: ignore
-    missing_return: ignore
-    override_on_non_overriding_getter: ignore
-    override_on_non_overriding_field: ignore
-    override_on_non_overriding_method: ignore
-    avoid_types_as_parameter_names: ignore
-    empty_catches: ignore
-    unawaited_futures: ignore
-    use_rethrow_when_possible: ignore
-    unused_import: ignore
-    must_be_immutable: ignore
-
+ strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
\ No newline at end of file
diff --git a/example/lib/main.dart b/example/lib/main.dart
index e89cc778..40942ea1 100644
--- a/example/lib/main.dart
+++ b/example/lib/main.dart
@@ -23,7 +23,7 @@ void main() {
 }
 
 class MyApp extends StatelessWidget {
-  var _helper = new SIPUAHelper();
+  final SIPUAHelper _helper = SIPUAHelper();
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
diff --git a/example/lib/src/callscreen.dart b/example/lib/src/callscreen.dart
index 9a5ccd2d..99716bbc 100644
--- a/example/lib/src/callscreen.dart
+++ b/example/lib/src/callscreen.dart
@@ -3,27 +3,27 @@ import 'package:flutter/material.dart';
 import 'package:flutter_webrtc/webrtc.dart';
 import 'sip_ua_helper.dart';
 import 'package:sip_ua/src/RTCSession.dart';
+import 'package:sip_ua/src/NameAddrHeader.dart';
 
 class CallScreenWidget extends StatefulWidget {
-  SIPUAHelper _helper;
+  final SIPUAHelper _helper;
   CallScreenWidget(this._helper, {Key key}) : super(key: key);
   @override
   _MyCallScreenWidget createState() => _MyCallScreenWidget();
 }
 
 class _MyCallScreenWidget extends State<CallScreenWidget> {
-  RTCVideoRenderer _localRenderer = new RTCVideoRenderer();
-  RTCVideoRenderer _remoteRenderer = new RTCVideoRenderer();
+  RTCVideoRenderer _localRenderer = RTCVideoRenderer();
+  RTCVideoRenderer _remoteRenderer = RTCVideoRenderer();
   double _localVideoHeight;
   double _localVideoWidth;
   EdgeInsetsGeometry _localVideoMargin;
-  var _localStream;
-  var _remoteStream;
-  var _direction;
-  var _local_identity;
-  var _remote_identity;
-  bool _showNumPad = false;
-  var _label;
+  MediaStream _localStream;
+  MediaStream _remoteStream;
+  String _direction;
+  NameAddrHeader _local_identity;
+  NameAddrHeader _remote_identity;
+
   var _timeLabel = '00:00';
   Timer _timer;
 
@@ -37,9 +37,9 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
 
   SIPUAHelper get helper => widget._helper;
 
-  get voiceonly =>
-      (_localStream == null || _localStream.getVideoTracks().length == 0) &&
-      (_remoteStream == null || _remoteStream.getVideoTracks().length == 0);
+  bool get voiceonly =>
+      (_localStream == null || _localStream.getVideoTracks().isEmpty) &&
+      (_remoteStream == null || _remoteStream.getVideoTracks().isEmpty);
 
   @override
   initState() {
@@ -59,7 +59,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     _disposeRenderers();
   }
 
-  _startTimer() {
+  void _startTimer() {
     _timer = Timer.periodic(Duration(seconds: 1), (Timer timer) {
       Duration duration = Duration(seconds: timer.tick);
       if (mounted) {
@@ -74,7 +74,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     });
   }
 
-  _initRenderers() async {
+  void _initRenderers() async {
     if (_localRenderer != null) {
       await _localRenderer.initialize();
     }
@@ -83,7 +83,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     }
   }
 
-  _disposeRenderers() {
+  void _disposeRenderers() {
     if (_localRenderer != null) {
       _localRenderer.dispose();
       _localRenderer = null;
@@ -94,28 +94,28 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     }
   }
 
-  _bindEventListeners() {
+  void _bindEventListeners() {
     helper.on('callState', _handleCalllState);
   }
 
-  _handleCalllState(state, data) {
+  void _handleCalllState(String state, Map<String, dynamic> data) {
     if (state == 'hold' || state == 'unhold') {
       _hold = state == 'hold';
-      _holdOriginator = data['originator'];
+      _holdOriginator = data['originator'] as String;
       this.setState(() {});
       return;
     }
 
     if (state == 'muted') {
-      if (data['audio']) _audioMuted = true;
-      if (data['video']) _videoMuted = true;
+      if (data['audio'] as bool) _audioMuted = true;
+      if (data['video'] as bool) _videoMuted = true;
       this.setState(() {});
       return;
     }
 
     if (state == 'unmuted') {
-      if (data['audio']) _audioMuted = false;
-      if (data['video']) _videoMuted = false;
+      if (data['audio'] as bool) _audioMuted = false;
+      if (data['video'] as bool) _videoMuted = false;
       this.setState(() {});
       return;
     }
@@ -140,19 +140,19 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     this.setState(() {});
   }
 
-  _removeEventListeners() {
+  void _removeEventListeners() {
     helper.remove('callState', _handleCalllState);
   }
 
-  _backToDialPad() {
+  void _backToDialPad() {
     _timer.cancel();
-    new Timer(Duration(seconds: 2), () {
+    Timer(Duration(seconds: 2), () {
       Navigator.of(context).pop();
     });
   }
 
-  _handelStreams(event) async {
-    var stream = event['stream'];
+  void _handelStreams(Map<String, dynamic> event) async {
+    var stream = event['stream'] as MediaStream;
     if (event['originator'] == 'local') {
       if (_localRenderer != null) {
         _localRenderer.srcObject = stream;
@@ -171,7 +171,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
     });
   }
 
-  _resizeLocalVideo() {
+  void _resizeLocalVideo() {
     _localVideoMargin = _remoteStream != null
         ? EdgeInsets.only(top: 15, right: 15)
         : EdgeInsets.all(0);
@@ -183,48 +183,51 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
         : MediaQuery.of(context).size.height;
   }
 
-  _handleHangup() {
+  void _handleHangup() {
     helper.hangup();
     _timer.cancel();
   }
 
-  _handleAccept() {
+  void _handleAccept() {
     helper.answer();
   }
 
-  _switchCamera() {
+  void _switchCamera() {
     if (_localStream != null) {
       _localStream.getVideoTracks()[0].switchCamera();
     }
   }
 
-  _muteAudio() {
-    if (_audioMuted)
+  void _muteAudio() {
+    if (_audioMuted) {
       helper.unmute(true, false);
-    else
+    } else {
       helper.mute(true, false);
+    }
   }
 
-  _muteVideo() {
-    if (_videoMuted)
+  void _muteVideo() {
+    if (_videoMuted) {
       helper.unmute(false, true);
-    else
+    } else {
       helper.mute(false, true);
+    }
   }
 
-  _handleHold() {
-    if (_hold)
+  void _handleHold() {
+    if (_hold) {
       helper.unhold();
-    else
+    } else {
       helper.hold();
+    }
   }
 
-  _buildActionButtons() {
+  Widget _buildActionButtons() {
     var hangupBtn = FloatingActionButton(
       heroTag: "hangup",
       onPressed: () => _handleHangup(),
       tooltip: 'Hangup',
-      child: new Icon(Icons.call_end),
+      child: Icon(Icons.call_end),
       backgroundColor: Colors.red,
     );
 
@@ -232,7 +235,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
       heroTag: "hangup",
       onPressed: () => _handleHangup(),
       tooltip: 'Hangup',
-      child: new Icon(Icons.call_end),
+      child: Icon(Icons.call_end),
       backgroundColor: Colors.grey,
     );
 
@@ -258,14 +261,14 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
         {
           advanceActions.add(FloatingActionButton(
             heroTag: "mute_mic",
-            child: new Icon(_audioMuted ? Icons.mic_off : Icons.mic),
+            child: Icon(_audioMuted ? Icons.mic_off : Icons.mic),
             onPressed: () => _muteAudio(),
           ));
 
           if (voiceonly) {
             advanceActions.add(FloatingActionButton(
               heroTag: "keypad",
-              child: new Icon(Icons.dialpad),
+              child: Icon(Icons.dialpad),
               onPressed: () => _handleHold(),
             ));
           } else {
@@ -279,21 +282,20 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
           if (voiceonly) {
             advanceActions.add(FloatingActionButton(
               heroTag: "speaker",
-              child: new Icon(Icons.volume_up),
+              child: Icon(Icons.volume_up),
               onPressed: () => _handleHold(),
             ));
           } else {
             advanceActions.add(FloatingActionButton(
               heroTag: "camera_off",
-              child:
-                  new Icon(_videoMuted ? Icons.videocam : Icons.videocam_off),
+              child: Icon(_videoMuted ? Icons.videocam : Icons.videocam_off),
               onPressed: () => _muteVideo(),
             ));
           }
 
           basicActions.add(FloatingActionButton(
             heroTag: "hold",
-            child: new Icon(_hold ? Icons.play_arrow : Icons.pause),
+            child: Icon(_hold ? Icons.play_arrow : Icons.pause),
             onPressed: () => _handleHold(),
           ));
 
@@ -301,7 +303,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
 
           basicActions.add(FloatingActionButton(
             heroTag: "transfer",
-            child: new Icon(Icons.phone_forwarded),
+            child: Icon(Icons.phone_forwarded),
             onPressed: () => _handleHold(),
           ));
         }
@@ -318,27 +320,27 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
 
     var actionWidgets = <Widget>[];
 
-    if (advanceActions.length > 0) {
+    if (advanceActions.isNotEmpty) {
       actionWidgets.add(Padding(
           padding: const EdgeInsets.all(3),
-          child: new Row(
+          child: Row(
               mainAxisAlignment: MainAxisAlignment.spaceEvenly,
               children: advanceActions)));
     }
 
     actionWidgets.add(Padding(
         padding: const EdgeInsets.all(3),
-        child: new Row(
+        child: Row(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: basicActions)));
 
-    return new Column(
+    return Column(
         crossAxisAlignment: CrossAxisAlignment.end,
         mainAxisAlignment: MainAxisAlignment.spaceEvenly,
         children: actionWidgets);
   }
 
-  _buildContent() {
+  Widget _buildContent() {
     var stackWidgets = <Widget>[];
 
     if (!voiceonly && _remoteStream != null) {
@@ -369,7 +371,7 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
           left: 0,
           right: 0,
           child: Center(
-              child: new Column(
+              child: Column(
             crossAxisAlignment: CrossAxisAlignment.center,
             mainAxisAlignment: MainAxisAlignment.center,
             children: <Widget>[
@@ -415,8 +417,8 @@ class _MyCallScreenWidget extends State<CallScreenWidget> {
         floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
         floatingActionButton: Padding(
           padding: const EdgeInsets.fromLTRB(0.0, 0.0, 0.0, 36.0),
-          child: new Container(
-              height: 128, width: 300, child: _buildActionButtons()),
+          child:
+              Container(height: 128, width: 300, child: _buildActionButtons()),
         ));
   }
 }
diff --git a/example/lib/src/dialpad.dart b/example/lib/src/dialpad.dart
index 3bf0d4c3..a5bdf58b 100644
--- a/example/lib/src/dialpad.dart
+++ b/example/lib/src/dialpad.dart
@@ -3,14 +3,14 @@ import 'package:shared_preferences/shared_preferences.dart';
 import 'sip_ua_helper.dart';
 
 class DialPadWidget extends StatefulWidget {
-  SIPUAHelper _helper;
+  final SIPUAHelper _helper;
   DialPadWidget(this._helper, {Key key}) : super(key: key);
   @override
   _MyDialPadWidget createState() => _MyDialPadWidget();
 }
 
 class _MyDialPadWidget extends State<DialPadWidget> {
-  var _dest;
+  String _dest;
   SIPUAHelper get helper => widget._helper;
   TextEditingController _textController;
   SharedPreferences prefs;
@@ -22,38 +22,38 @@ class _MyDialPadWidget extends State<DialPadWidget> {
     _loadSettings();
   }
 
-  _loadSettings() async {
+  void _loadSettings() async {
     prefs = await SharedPreferences.getInstance();
     _dest = prefs.getString('dest') ?? 'sip:111_6ackea@tryit.jssip.net';
-    _textController = new TextEditingController(text: _dest);
+    _textController = TextEditingController(text: _dest);
     _textController.text = _dest;
-    this.setState((){});
+    this.setState(() {});
   }
 
-  _handleRegisterState(state, data) {
+  void _handleRegisterState(String state, Map<String, dynamic> data) {
     this.setState(() {});
   }
 
-  _bindEventListeners() {
+  void _bindEventListeners() {
     helper.on('registerState', _handleRegisterState);
-    helper.on('uaState', (state, data) {
+    helper.on('uaState', (String state, Map<String, dynamic> data) {
       if (state == 'newRTCSession') Navigator.pushNamed(context, '/callscreen');
     });
   }
 
-  _handleCall(context, [voiceonly]) {
+  Widget _handleCall(BuildContext context, [bool voiceonly]) {
     var dest = _textController.text;
-    if (dest == null || dest.length == 0) {
+    if (dest == null || dest.isEmpty) {
       showDialog<Null>(
         context: context,
         barrierDismissible: false,
         builder: (BuildContext context) {
-          return new AlertDialog(
-            title: new Text('Target is empty.'),
-            content: new Text('Please enter a SIP URI or username!'),
+          return AlertDialog(
+            title: Text('Target is empty.'),
+            content: Text('Please enter a SIP URI or username!'),
             actions: <Widget>[
-              new FlatButton(
-                child: new Text('Ok'),
+              FlatButton(
+                child: Text('Ok'),
                 onPressed: () {
                   Navigator.of(context).pop();
                 },
@@ -62,15 +62,16 @@ class _MyDialPadWidget extends State<DialPadWidget> {
           );
         },
       );
-      return;
+      return null;
     }
-    helper.connect(dest, voiceonly);
+    helper.call(dest, voiceonly);
     prefs.setString('dest', dest);
+    return null;
   }
 
-  _handleBackSpace() {
+  void _handleBackSpace() {
     var text = _textController.text;
-    if (text.length > 0) {
+    if (text.isNotEmpty) {
       this.setState(() {
         text = text.substring(0, text.length - 1);
         _textController.text = text;
@@ -78,13 +79,13 @@ class _MyDialPadWidget extends State<DialPadWidget> {
     }
   }
 
-  _handleNum(number) {
+  void _handleNum(String number) {
     this.setState(() {
       _textController.text += number;
     });
   }
 
-  _buildDialPad() {
+  List<Widget> _buildDialPad() {
     var lables = [
       [
         {'1': ''},
@@ -127,24 +128,24 @@ class _MyDialPadWidget extends State<DialPadWidget> {
                       controller: _textController,
                     )),
               ])),
-      new Container(
+      Container(
           width: 300,
-          child: new Column(
+          child: Column(
               crossAxisAlignment: CrossAxisAlignment.center,
               mainAxisAlignment: MainAxisAlignment.center,
               children: lables
-                  .map((row) => new Padding(
+                  .map((row) => Padding(
                       padding: const EdgeInsets.all(3),
-                      child: new Row(
+                      child: Row(
                           mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                           children: row
-                              .map((label) => new Container(
+                              .map((label) => Container(
                                   height: 72,
                                   width: 72,
-                                  child: new FlatButton(
+                                  child: FlatButton(
                                     //heroTag: "num_$label",
                                     shape: CircleBorder(),
-                                    child: new Column(
+                                    child: Column(
                                         mainAxisAlignment:
                                             MainAxisAlignment.center,
                                         children: <Widget>[
@@ -168,7 +169,7 @@ class _MyDialPadWidget extends State<DialPadWidget> {
                   .toList())),
       Container(
           width: 300,
-          child: new Row(
+          child: Row(
             crossAxisAlignment: CrossAxisAlignment.center,
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: <Widget>[
@@ -197,7 +198,7 @@ class _MyDialPadWidget extends State<DialPadWidget> {
         appBar: AppBar(
           title: Text("Dart SIP UA Demo"),
           actions: <Widget>[
-            new PopupMenuButton<String>(
+            PopupMenuButton<String>(
                 onSelected: (String value) {
                   switch (value) {
                     case 'account':
@@ -213,18 +214,18 @@ class _MyDialPadWidget extends State<DialPadWidget> {
                 icon: Icon(Icons.menu),
                 itemBuilder: (BuildContext context) => <PopupMenuEntry<String>>[
                       PopupMenuItem(
-                        child: new Row(
+                        child: Row(
                           mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                           children: <Widget>[
                             Padding(
                               padding: const EdgeInsets.fromLTRB(0, 0, 0, 0),
-                              child: new Icon(
+                              child: Icon(
                                 Icons.account_circle,
                                 color: Colors.black38,
                               ),
                             ),
                             SizedBox(
-                              child: new Text('Account'),
+                              child: Text('Account'),
                               width: 64,
                             )
                           ],
@@ -232,15 +233,15 @@ class _MyDialPadWidget extends State<DialPadWidget> {
                         value: 'account',
                       ),
                       PopupMenuItem(
-                        child: new Row(
+                        child: Row(
                           mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                           children: <Widget>[
-                            new Icon(
+                            Icon(
                               Icons.info,
                               color: Colors.black38,
                             ),
                             SizedBox(
-                              child: new Text('About'),
+                              child: Text('About'),
                               width: 64,
                             )
                           ],
@@ -264,8 +265,8 @@ class _MyDialPadWidget extends State<DialPadWidget> {
                       style: TextStyle(fontSize: 14, color: Colors.black54),
                     )),
                   ),
-                  new Container(
-                      child: new Column(
+                  Container(
+                      child: Column(
                     crossAxisAlignment: CrossAxisAlignment.center,
                     mainAxisAlignment: MainAxisAlignment.center,
                     children: _buildDialPad(),
diff --git a/example/lib/src/register.dart b/example/lib/src/register.dart
index 945ebbf9..26d5f47e 100644
--- a/example/lib/src/register.dart
+++ b/example/lib/src/register.dart
@@ -3,25 +3,25 @@ import 'package:shared_preferences/shared_preferences.dart';
 import 'sip_ua_helper.dart';
 
 class RegisterWidget extends StatefulWidget {
-  SIPUAHelper _helper;
+  final SIPUAHelper _helper;
   RegisterWidget(this._helper, {Key key}) : super(key: key);
   @override
   _MyRegisterWidget createState() => _MyRegisterWidget();
 }
 
 class _MyRegisterWidget extends State<RegisterWidget> {
-  var _password;
-  var _wsUri;
-  var _sipUri;
-  var _displayName;
-  var _wsExtraHeaders = {
+  String _password;
+  String _wsUri;
+  String _sipUri;
+  String _displayName;
+  Map<String, String> _wsExtraHeaders = {
     'Origin': ' https://tryit.jssip.net',
     'Host': 'tryit.jssip.net:10443'
   };
   SharedPreferences prefs;
-  var _registerState;
+  String _registerState;
 
-  get helper => widget._helper;
+  SIPUAHelper get helper => widget._helper;
 
   @override
   initState() {
@@ -40,46 +40,46 @@ class _MyRegisterWidget extends State<RegisterWidget> {
     _saveSettings();
   }
 
-  _loadSettings() async {
+  void _loadSettings() async {
     prefs = await SharedPreferences.getInstance();
-    _wsUri = prefs.getString('ws_uri') ?? 'wss://tryit.jssip.net:10443';
-    _sipUri = prefs.getString('sip_uri') ?? 'hello_flutter@tryit.jssip.net';
-    _displayName = prefs.getString('display_name') ?? 'Flutter SIP UA';
-    _password = prefs.getString('password');
-    prefs.commit();
-    this.setState(() {});
+    this.setState(() {
+      _wsUri = prefs.getString('ws_uri') ?? 'wss://tryit.jssip.net:10443';
+      _sipUri = prefs.getString('sip_uri') ?? 'hello_flutter@tryit.jssip.net';
+      _displayName = prefs.getString('display_name') ?? 'Flutter SIP UA';
+      _password = prefs.getString('password');
+    });
   }
 
-  _saveSettings() {
+  void _saveSettings() {
     prefs.setString('ws_uri', _wsUri);
     prefs.setString('sip_uri', _sipUri);
     prefs.setString('display_name', _displayName);
     prefs.setString('password', _password);
   }
 
-  _handleRegisterState(state, data) {
+  void _handleRegisterState(String state, Map<String, dynamic> data) {
     this.setState(() {
       _registerState = state;
     });
   }
 
-  _handleSocketState(state, data) {
+  void _handleSocketState(String state, Map<String, dynamic> data) {
     this.setState(() {
       _registerState = state;
     });
   }
 
-  _alert(context, alertFieldName) {
+  void _alert(BuildContext context, String alertFieldName) {
     showDialog<Null>(
       context: context,
       barrierDismissible: false,
       builder: (BuildContext context) {
-        return new AlertDialog(
-          title: new Text('$alertFieldName is empty'),
-          content: new Text('Please enter $alertFieldName!'),
+        return AlertDialog(
+          title: Text('$alertFieldName is empty'),
+          content: Text('Please enter $alertFieldName!'),
           actions: <Widget>[
-            new FlatButton(
-              child: new Text('Ok'),
+            FlatButton(
+              child: Text('Ok'),
               onPressed: () {
                 Navigator.of(context).pop();
               },
@@ -90,13 +90,13 @@ class _MyRegisterWidget extends State<RegisterWidget> {
     );
   }
 
-  _handleSave(context) {
+  void _handleSave(BuildContext context) {
     if (_wsUri == null) {
-      return _alert(context, "WebSocket URL");
+      _alert(context, "WebSocket URL");
     } else if (_sipUri == null) {
-      return _alert(context, "SIP URI");
+      _alert(context, "SIP URI");
     }
-    bool addExtraHeaders = (_wsUri == 'wss://tryit.jssip.net:10443');
+    bool addExtraHeaders = _wsExtraHeaders.isNotEmpty;
     helper.start(_wsUri, _sipUri, _password, _displayName,
         addExtraHeaders ? _wsExtraHeaders : null);
   }
@@ -107,7 +107,7 @@ class _MyRegisterWidget extends State<RegisterWidget> {
         appBar: AppBar(
           title: Text("SIP Account"),
         ),
-        body: new Align(
+        body: Align(
             alignment: Alignment(0, 0),
             child: Column(
                 crossAxisAlignment: CrossAxisAlignment.center,
diff --git a/example/lib/src/sip_ua_helper.dart b/example/lib/src/sip_ua_helper.dart
index 4b9cfe70..71bac859 100644
--- a/example/lib/src/sip_ua_helper.dart
+++ b/example/lib/src/sip_ua_helper.dart
@@ -2,23 +2,20 @@ import 'dart:async';
 import 'package:sip_ua/sip_ua.dart';
 import 'package:events2/events2.dart';
 import 'package:sip_ua/src/RTCSession.dart';
+import 'package:sip_ua/src/Message.dart';
 
 class SIPUAHelper extends EventEmitter {
   UA _ua;
   Settings _settings;
-  final logger = new Logger('SIPUA::Helper');
+  final logger = Logger('SIPUA::Helper');
   RTCSession _session;
   bool _registered = false;
   bool _connected = false;
   var _registerState = 'new';
-  var _localStream;
-  var _remoteStream;
 
-  SIPUAHelper();
+  void debug(dynamic msg) => logger.debug(msg);
 
-  debug(msg) => logger.debug(msg);
-
-  debugerror(error) => logger.error(error);
+  void debugerror(dynamic error) => logger.error(error);
 
   RTCSession get session => _session;
 
@@ -26,99 +23,117 @@ class SIPUAHelper extends EventEmitter {
 
   bool get connected => _connected;
 
-  get registerState => _registerState;
+  String get registerState => _registerState;
 
-  get localStream => _localStream;
+  void stop() async {
+    await this._ua.stop();
+  }
 
-  get remoteStream => _remoteStream;
+  void register() {
+    this._ua.register();
+  }
 
-  _handleSocketState(state, data) {
-    this.emit('socketState', state, data);
+  void unregister([bool all = true]) {
+    this._ua.unregister(all: all);
   }
 
-  _handleRegisterState(state, data) {
-    this.emit('registerState', state, data);
+  Future<RTCSession> call(String uri, [bool voiceonly = false]) async {
+    if (_ua != null && _ua.isConnected()) {
+      _session = _ua.call(uri, this._options(voiceonly));
+      return _session;
+    } else {
+      logger.error("Not connected, you will need to register.");
+    }
+    return null;
   }
 
-  _handleUAState(state, data) {
-    this.emit('uaState', state, data);
+  void answer() {
+    if (_session != null) {
+      _session.answer(this._options());
+    }
   }
 
-  _handleCallState(state, data) {
-    this.emit('callState', state, data);
+  void hangup() {
+    if (_session != null) {
+      _session.terminate();
+    }
   }
 
-  start(wsUrl, uri, [password, displayName, wsExtraHeaders]) async {
+  void start(String wsUrl, String uri,
+      [String password,
+      String displayName,
+      Map<String, dynamic> wsExtraHeaders]) async {
     if (this._ua != null) {
       debugerror(
           'UA instance already exist!, stopping UA and creating a new one...');
       this._ua.stop();
     }
-    _settings = new Settings();
-    var socket = new WebSocketInterface(wsUrl, wsExtraHeaders);
+    _settings = Settings();
+    var socket = WebSocketInterface(wsUrl, wsExtraHeaders);
     _settings.sockets = [socket];
     _settings.uri = uri;
     _settings.password = password;
     _settings.display_name = displayName;
 
     try {
-      this._ua = new UA(_settings);
-      this._ua.on('onnecting', (data) {
+      this._ua = UA(_settings);
+      this._ua.on('onnecting', (Map<String, dynamic> data) {
         debug('onnecting => ' + data.toString());
         _handleSocketState('onnecting', data);
       });
 
-      this._ua.on('connected', (data) {
+      this._ua.on('connected', (Map<String, dynamic> data) {
         debug('connected => ' + data.toString());
         _handleSocketState('connected', data);
         _connected = true;
       });
 
-      this._ua.on('disconnected', (data) {
+      this._ua.on('disconnected', (Map<String, dynamic> data) {
         debug('disconnected => ' + data.toString());
         _handleSocketState('disconnected', data);
         _connected = false;
       });
 
-      this._ua.on('registered', (data) {
+      this._ua.on('registered', (Map<String, dynamic> data) {
         debug('registered => ' + data.toString());
         _registered = true;
         _registerState = 'registered';
         _handleRegisterState('registered', data);
       });
 
-      this._ua.on('unregistered', (data) {
+      this._ua.on('unregistered', (Map<String, dynamic> data) {
         debug('unregistered => ' + data.toString());
         _registerState = 'unregistered';
         _registered = false;
         _handleRegisterState('unregistered', data);
       });
 
-      this._ua.on('registrationFailed', (data) {
-        debug('registrationFailed => ' + data['cause']);
+      this._ua.on('registrationFailed', (Map<String, dynamic> data) {
+        debug('registrationFailed => ' + (data['cause'] as String));
         _registerState = 'registrationFailed[${data['cause']}]';
         _registered = false;
         _handleRegisterState('registrationFailed', data);
       });
 
-      this._ua.on('newRTCSession', (data) {
+      this._ua.on('newRTCSession', (Map<String, dynamic> data) {
         debug('newRTCSession => ' + data.toString());
-        _session = data['session'];
+        _session = data['session'] as RTCSession;
         if (_session.direction == 'incoming') {
           // Set event handlers.
-          options()['eventHandlers'].forEach((event, func) {
+          (_options()['eventHandlers'] as Map<String, Function>)
+              .forEach((String event, Function func) {
             _session.on(event, func);
           });
         }
         _handleUAState('newRTCSession', data);
       });
 
-      this._ua.on('newMessage', (data) {
+      this._ua.on('newMessage', (Map<String, dynamic> data) {
         debug('newMessage => ' + data.toString());
         _handleUAState('newMessage', data);
       });
 
-      this._ua.on('sipEvent', (data) {
+      this._ua.on('sipEvent', (Map<String, dynamic> data) {
         debug('sipEvent => ' + data.toString());
         _handleUAState('sipEvent', data);
       });
@@ -128,90 +143,73 @@ class SIPUAHelper extends EventEmitter {
     }
   }
 
-  stop() async {
-    await this._ua.stop();
-  }
-
-  register() {
-    this._ua.register();
-  }
-
-  unregister([all = true]) {
-    this._ua.unregister(all: all);
-  }
-
-  options([voiceonly]) {
-    voiceonly = voiceonly ?? false;
+  Map<String, Object> _options([bool voiceonly = false]) {
     // Register callbacks to desired call events
     var eventHandlers = {
-      'connecting': (e) {
+      'connecting': (Map<String, dynamic> e) {
         debug('call connecting');
         _handleCallState('connecting', e);
       },
-      'progress': (e) {
+      'progress': (Map<String, dynamic> e) {
         debug('call is in progress');
         _handleCallState('progress', e);
       },
-      'failed': (e) {
-        debug('call failed with cause: ' + e['cause']);
+      'failed': (Map<String, dynamic> e) {
+        debug('call failed with cause: ' + (e['cause'] as String));
         _handleCallState('failed', e);
         _session = null;
         var cause = 'failed (${e['cause']})';
-        _localStream = null;
-        _remoteStream = null;
       },
-      'ended': (e) {
-        debug('call ended with cause: ' + e['cause']);
+      'ended': (Map<String, dynamic> e) {
+        debug('call ended with cause: ' + (e['cause'] as String));
         _handleCallState('ended', e);
         _session = null;
-        _localStream = null;
-        _remoteStream = null;
       },
-      'accepted': (e) {
+      'accepted': (Map<String, dynamic> e) {
         debug('call accepted');
         _handleCallState('accepted', e);
       },
-      'confirmed': (e) {
+      'confirmed': (Map<String, dynamic> e) {
         debug('call confirmed');
         _handleCallState('confirmed', e);
       },
-      'hold': (e) {
+      'hold': (Map<String, dynamic> e) {
         debug('call hold');
         _handleCallState('hold', e);
       },
-      'unhold': (e) {
+      'unhold': (Map<String, dynamic> e) {
         debug('call unhold');
         _handleCallState('unhold', e);
       },
-      'muted': (e) {
+      'muted': (Map<String, dynamic> e) {
         debug('call muted');
         _handleCallState('muted', e);
       },
-      'unmuted': (e) {
+      'unmuted': (Map<String, dynamic> e) {
         debug('call unmuted');
         _handleCallState('unmuted', e);
       },
-      'stream': (e) async {
+      'stream': (Map<String, dynamic> e) async {
         // Wating for callscreen ready.
-        new Timer(Duration(milliseconds: 100), () {
+        Timer(Duration(milliseconds: 100), () {
           _handleCallState('stream', e);
         });
       }
     };
 
-    var defaultOptions = {
+    var _defaultOptions = {
       'eventHandlers': eventHandlers,
       'pcConfig': {
         'iceServers': [
           {'url': 'stun:stun.l.google.com:19302'},
           /*
-          * turn server configuration example.
-          {
-            'url': 'turn:123.45.67.89:3478',
-            'username': 'change_to_real_user',
-            'credential': 'change_to_real_secret'
-          },
-          */
+                  * turn server configuration example.
+                  {
+                    'url': 'turn:123.45.67.89:3478',
+                    'username': 'change_to_real_user',
+                    'credential': 'change_to_real_secret'
+                  },
+                  */
         ]
       },
       'mediaConstraints': {
@@ -225,7 +223,7 @@ class SIPUAHelper extends EventEmitter {
                   "minFrameRate": '30',
                 },
                 "facingMode": "user",
-                "optional": [],
+                "optional": List<dynamic>(),
               }
       },
       'rtcOfferConstraints': {
@@ -233,77 +231,72 @@ class SIPUAHelper extends EventEmitter {
           'OfferToReceiveAudio': true,
           'OfferToReceiveVideo': !voiceonly,
         },
-        'optional': [],
+        'optional': List<dynamic>(),
       },
       'rtcAnswerConstraints': {
         'mandatory': {
           'OfferToReceiveAudio': true,
           'OfferToReceiveVideo': true,
         },
-        'optional': [],
+        'optional': List<dynamic>(),
       },
       'rtcConstraints': {
-        'mandatory': {},
+        'mandatory': Map<dynamic, dynamic>(),
         'optional': [
           {'DtlsSrtpKeyAgreement': true},
         ],
       },
       'sessionTimersExpires': 120
     };
-    return defaultOptions;
+    return _defaultOptions;
   }
 
-  connect(uri, [voiceonly]) async {
-    if (_ua != null && _ua.isConnected()) {
-      _session = _ua.call(uri, this.options(voiceonly));
-      return _session;
-    } else {
-      logger.error("Not connected, you will need to register.");
-    }
-    return null;
-  }
-
-  answer() {
-    if (_session != null) {
-      _session.answer(this.options());
-    }
+  void _handleSocketState(String state, Map<String, dynamic> data) {
+    this.emit('socketState', state, data);
   }
 
-  hangup() {
-    if (_session != null) {
-      _session.terminate();
-    }
+  void _handleRegisterState(String state, Map<String, dynamic> data) {
+    this.emit('registerState', state, data);
   }
 
-  hold() {
+  void hold() {
     if (_session != null) {
       _session.hold();
     }
   }
 
-  unhold() {
+  void unhold() {
     if (_session != null) {
       _session.unhold();
     }
   }
 
-  mute([audio = true, video = true]) {
+  void mute([bool audio = true, bool video = true]) {
     if (_session != null) {
       _session.mute(audio, video);
     }
   }
 
-  unmute([audio = true, video = true]) {
+  void unmute([bool audio = true, bool video = true]) {
     if (_session != null) {
       _session.unmute(audio, video);
     }
   }
 
-  sendMessage(target, body, [options]) {
+  void _handleCallState(String state, Map<String, dynamic> data) {
+    this.emit('callState', state, data);
+  }
+
+  void _handleUAState(String state, Map<String, dynamic> data) {
+    this.emit('uaState', state, data);
+  }
+
+  Message sendMessage(String target, String body,
+      [Map<String, dynamic> options]) {
     return this._ua.sendMessage(target, body, options);
   }
 
-  terminateSessions(options) {
-    return this._ua.terminateSessions(options);
+  void terminateSessions(Map<String, dynamic> options) {
+    this._ua.terminateSessions(options);
   }
 }
diff --git a/example/test/test2_websocket.dart b/example/test/test2_websocket.dart
new file mode 100644
index 00000000..5ace168f
--- /dev/null
+++ b/example/test/test2_websocket.dart
@@ -0,0 +1,52 @@
+import 'dart:async';
+import 'dart:io';
+
+void main() async {
+  TestWebsocket2 tester = TestWebsocket2();
+  tester.connect("wss://echo.websocket.org/");
+
+  await tester.finished.future;
+}
+
+class TestWebsocket2 {
+  bool connected = false;
+  WebSocket ws;
+  Completer completer;
+  int ctr = 1;
+
+  Completer finished = Completer<String>();
+
+  void send() {
+    String message = "A" * ctr;
+    ws.add(message);
+    completer = Completer<String>();
+    completer.future.then((dynamic t) {
+      ctr += 7;
+      if (ctr > 5000 || finished.isCompleted) {
+        finished.complete();
+      } else {
+        send();
+      }
+    });
+  }
+
+  void connect(String url) async {
+    ws = await WebSocket.connect(url);
+    connected = true;
+    ws.listen((dynamic data) {
+      this._onMessage(data as String);
+    }, onDone: () {
+      print('Closed by server [${ws.closeCode}, ${ws.closeReason}]!');
+      connected = false;
+    });
+    send();
+  }
+
+  void _onMessage(String data) {
+    print("Received data of size ${data.length} expected ${ctr}");
+    if (data.length != ctr) {
+      finished.complete();
+    }
+    completer.complete();
+  }
+}
diff --git a/lib/src/Config.dart b/lib/src/Config.dart
index 0568e9c5..b8d787ae 100644
--- a/lib/src/Config.dart
+++ b/lib/src/Config.dart
@@ -1,12 +1,11 @@
-import 'package:sip_ua/sip_ua.dart';
-
+import '../sip_ua.dart';
 import 'Constants.dart';
-import 'Utils.dart' as Utils;
 import 'Constants.dart' as DartSIP_C;
+import 'Exceptions.dart' as Exceptions;
 import 'Grammar.dart';
-import 'URI.dart';
 import 'Socket.dart' as Socket;
-import 'Exceptions.dart' as Exceptions;
+import 'URI.dart';
+import 'Utils.dart' as Utils;
 import 'logger.dart';
 
   final logger = Logger('Config');
diff --git a/lib/src/Dialog.dart b/lib/src/Dialog.dart
index 6bfe3b03..f81b5d44 100644
--- a/lib/src/Dialog.dart
+++ b/lib/src/Dialog.dart
@@ -1,5 +1,3 @@
-import 'package:sip_ua/src/transactions/transaction_base.dart';
-
 import '../sip_ua.dart';
 import 'Constants.dart';
 import 'Dialog/RequestSender.dart';
@@ -8,6 +6,7 @@ import 'RTCSession.dart';
 import 'SIPMessage.dart' as SIPMessage;
 import 'Utils.dart' as Utils;
 import 'logger.dart';
+import 'transactions/transaction_base.dart';
 
 class Dialog_C {
   // Dialog states.
diff --git a/lib/src/Dialog/RequestSender.dart b/lib/src/Dialog/RequestSender.dart
index 7f95c6ab..d20fc99d 100644
--- a/lib/src/Dialog/RequestSender.dart
+++ b/lib/src/Dialog/RequestSender.dart
@@ -1,5 +1,3 @@
-import 'package:sip_ua/src/transactions/transaction_base.dart';
-
 import '../../sip_ua.dart';
 import '../Constants.dart';
 import '../Dialog.dart';
@@ -7,6 +5,7 @@ import '../RTCSession.dart' as RTCSession;
 import '../RequestSender.dart';
 import '../SIPMessage.dart';
 import '../Timers.dart';
+import '../transactions/transaction_base.dart';
 
 // Default event handlers.
 var EventHandlers = {
diff --git a/lib/src/Grammar.dart b/lib/src/Grammar.dart
index b412de54..a3962466 100644
--- a/lib/src/Grammar.dart
+++ b/lib/src/Grammar.dart
@@ -1,6 +1,7 @@
-import 'package:sip_ua/src/grammar_parser.dart';
 import "package:parser_error/parser_error.dart";
 
+import 'grammar_parser.dart';
+
 class Grammar {
   static parse(String input,String startRule) {
     var parser = new GrammarParser('');
diff --git a/lib/src/Message.dart b/lib/src/Message.dart
index 98195cbe..259e78d5 100644
--- a/lib/src/Message.dart
+++ b/lib/src/Message.dart
@@ -1,11 +1,12 @@
 import 'package:events2/events2.dart';
+
 import '../sip_ua.dart';
 import 'Constants.dart' as DartSIP_C;
 import 'Constants.dart';
+import 'Exceptions.dart' as Exceptions;
+import 'RequestSender.dart';
 import 'SIPMessage.dart' as SIPMessage;
 import 'Utils.dart' as Utils;
-import 'RequestSender.dart';
-import 'Exceptions.dart' as Exceptions;
 import 'logger.dart';
 
 class Message extends EventEmitter {
@@ -45,7 +46,7 @@ class Message extends EventEmitter {
 
   get data => this._data;
 
-  send(target, body, [options]) {
+  send(String target, String body, [Map<String, dynamic> options]) {
     var originalTarget = target;
     options = options ?? {};
 
diff --git a/lib/src/Parser.dart b/lib/src/Parser.dart
index 8c401fb6..636c70a0 100644
--- a/lib/src/Parser.dart
+++ b/lib/src/Parser.dart
@@ -1,7 +1,6 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/SIPMessage.dart';
-
+import '../sip_ua.dart';
 import 'Grammar.dart';
+import 'SIPMessage.dart';
 import 'SIPMessage.dart' as SIPMessage;
 import 'logger.dart';
 
diff --git a/lib/src/RTCSession.dart b/lib/src/RTCSession.dart
index 0a29286d..b8d601ad 100644
--- a/lib/src/RTCSession.dart
+++ b/lib/src/RTCSession.dart
@@ -3,13 +3,13 @@ import 'dart:async';
 import 'package:events2/events2.dart';
 import 'package:flutter_webrtc/webrtc.dart';
 import 'package:sdp_transform/sdp_transform.dart' as sdp_transform;
-import 'package:sip_ua/src/transactions/transaction_base.dart';
 
 import '../sip_ua.dart';
 import 'Constants.dart';
 import 'Constants.dart' as DartSIP_C;
 import 'Dialog.dart';
 import 'Exceptions.dart' as Exceptions;
+import 'NameAddrHeader.dart';
 import 'RTCSession/DTMF.dart' as RTCSession_DTMF;
 import 'RTCSession/Info.dart' as RTCSession_Info;
 import 'RTCSession/ReferNotifier.dart' as RTCSession_ReferNotifier;
@@ -21,6 +21,7 @@ import 'Timers.dart';
 import 'URI.dart';
 import 'Utils.dart' as Utils;
 import 'logger.dart';
+import 'transactions/transaction_base.dart';
 
 class C {
   // RTCSession states.
@@ -83,7 +84,7 @@ class RTCSession extends EventEmitter {
   var _iceGatheringState;
   bool _localMediaStreamLocallyGenerated;
   bool _rtcReady;
-  var _direction;
+  String _direction;
 
   Map _referSubscribers;
   var _start_time;
@@ -94,8 +95,8 @@ class RTCSession extends EventEmitter {
   bool _localHold;
   bool _remoteHold;
 
-  var _local_identity;
-  var _remote_identity;
+  NameAddrHeader _local_identity;
+  NameAddrHeader _remote_identity;
 
   String _contact;
   var _tones;
@@ -195,11 +196,11 @@ class RTCSession extends EventEmitter {
 
   get contact => this._contact;
 
-  get direction => this._direction;
+  String get direction => this._direction;
 
-  get local_identity => this._local_identity;
+  NameAddrHeader get local_identity => this._local_identity;
 
-  get remote_identity => this._remote_identity;
+  NameAddrHeader get remote_identity => this._remote_identity;
 
   get start_time => this._start_time;
 
@@ -677,7 +678,7 @@ class RTCSession extends EventEmitter {
   /**
    * Terminate the call.
    */
-  terminate([options]) {
+  terminate([Map<String, Object> options]) {
     debug('terminate()');
 
     options = options ?? {};
@@ -687,7 +688,7 @@ class RTCSession extends EventEmitter {
     var body = options['body'];
 
     var cancel_reason;
-    var status_code = options['status_code'];
+    int status_code = options['status_code'];
     var reason_phrase = options['reason_phrase'];
 
     // Check Session Status.
@@ -1631,7 +1632,7 @@ class RTCSession extends EventEmitter {
   /**
    * Dialog Management
    */
-  _createDialog(message, type, [early]) {
+  bool _createDialog(message, type, [early]) {
     var local_tag = (type == 'UAS') ? message.to_tag : message.from_tag;
     var remote_tag = (type == 'UAS') ? message.from_tag : message.to_tag;
     var id = message.call_id + local_tag + remote_tag;
@@ -1679,7 +1680,7 @@ class RTCSession extends EventEmitter {
   }
 
   /// In dialog INVITE Reception
-  _receiveReinvite(request) async {
+  void _receiveReinvite(request) async {
     debug('receiveReinvite()');
 
     var contentType = request.getHeader('Content-Type');
@@ -1714,7 +1715,7 @@ class RTCSession extends EventEmitter {
 
     this._late_sdp = false;
 
-    sendAnswer(sdp) async {
+    void sendAnswer(String sdp) async {
       var extraHeaders = ['Contact: ${this._contact}'];
 
       this._handleSessionTimersInIncomingRequest(request, extraHeaders);
@@ -1771,7 +1772,7 @@ class RTCSession extends EventEmitter {
   /**
    * In dialog UPDATE Reception
    */
-  _receiveUpdate(request) async {
+  void _receiveUpdate(request) async {
     debug('receiveUpdate()');
 
     var rejected = false;
@@ -1814,7 +1815,7 @@ class RTCSession extends EventEmitter {
       return;
     }
 
-    if (request.body == null || request.body.length  == 0) {
+    if (request.body == null || request.body.length == 0) {
       sendAnswer(null);
       return;
     }
@@ -2501,11 +2502,15 @@ class RTCSession extends EventEmitter {
     if (sdpOffer) {
       extraHeaders.add('Content-Type: application/sdp');
       try {
-        var desc =
+        RTCSessionDescription desc =
             await this._createLocalDescription('offer', rtcOfferConstraints);
-        var sdp = this._mangleOffer(desc.sdp);
+        String sdp = this._mangleOffer(desc.sdp);
 
-        var e = {'originator': 'local', 'type': 'offer', 'sdp': sdp};
+        Map<String, String> e = {
+          'originator': 'local',
+          'type': 'offer',
+          'sdp': sdp
+        };
 
         debug('emit "sdp"');
         this.emit('sdp', e);
@@ -2585,12 +2590,12 @@ class RTCSession extends EventEmitter {
   /**
    * Correctly set the SDP direction attributes if the call is on local hold
    */
-  _mangleOffer(sdp) {
+  String _mangleOffer(String sdpInput) {
     if (!this._localHold && !this._remoteHold) {
-      return sdp;
+      return sdpInput;
     }
 
-    sdp = sdp_transform.parse(sdp);
+    Map<String, dynamic> sdp = sdp_transform.parse(sdpInput);
 
     // Local hold.
     if (this._localHold && !this._remoteHold) {
diff --git a/lib/src/RTCSession/ReferSubscriber.dart b/lib/src/RTCSession/ReferSubscriber.dart
index ec541c00..f1d9a4f2 100644
--- a/lib/src/RTCSession/ReferSubscriber.dart
+++ b/lib/src/RTCSession/ReferSubscriber.dart
@@ -1,4 +1,5 @@
 import 'package:events2/events2.dart';
+
 import '../Constants.dart' as DartSIP_C;
 import '../Constants.dart';
 import '../Grammar.dart';
diff --git a/lib/src/Registrator.dart b/lib/src/Registrator.dart
index 102294cb..a4716068 100644
--- a/lib/src/Registrator.dart
+++ b/lib/src/Registrator.dart
@@ -321,7 +321,7 @@ class Registrator {
 
     if (this._registered) {
       this._registered = false;
-      this._ua.unregistered({});
+      this._ua.unregistered(Map<String, dynamic>());
     }
   }
 
diff --git a/lib/src/RequestSender.dart b/lib/src/RequestSender.dart
index 2466f8b9..a280a6d3 100644
--- a/lib/src/RequestSender.dart
+++ b/lib/src/RequestSender.dart
@@ -1,15 +1,14 @@
 
 
-import 'package:sip_ua/src/transactions/ack_client.dart';
-import 'package:sip_ua/src/transactions/invite_client.dart';
-import 'package:sip_ua/src/transactions/non_invite_client.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
-
 import '../sip_ua.dart';
 import 'Constants.dart';
 import 'DigestAuthentication.dart';
 import 'UA.dart' as UAC;
 import 'logger.dart';
+import 'transactions/ack_client.dart';
+import 'transactions/invite_client.dart';
+import 'transactions/non_invite_client.dart';
+import 'transactions/transaction_base.dart';
 
 // Default event handlers.
 var EventHandlers = {
diff --git a/lib/src/SIPMessage.dart b/lib/src/SIPMessage.dart
index 99b0f96c..e14a2285 100644
--- a/lib/src/SIPMessage.dart
+++ b/lib/src/SIPMessage.dart
@@ -1,11 +1,12 @@
 import 'package:sdp_transform/sdp_transform.dart' as sdp_transform;
+
 import '../sip_ua.dart';
 import 'Constants.dart';
-import 'NameAddrHeader.dart';
+import 'Constants.dart' as DartSIP_C;
 import 'Exceptions.dart' as Exceptions;
 import 'Grammar.dart';
+import 'NameAddrHeader.dart';
 import 'Utils.dart' as Utils;
-import 'Constants.dart' as DartSIP_C;
 import 'logger.dart';
 
 final logger = Logger('SIPMessage');
diff --git a/lib/src/Transport.dart b/lib/src/Transport.dart
index 65b4efbd..69a56a87 100644
--- a/lib/src/Transport.dart
+++ b/lib/src/Transport.dart
@@ -1,11 +1,8 @@
-import 'dart:io';
-
-import 'package:sip_ua/src/WebSocketInterface.dart';
-
-import 'Socket.dart' as Socket;
 import 'Exceptions.dart' as Exceptions;
-import 'Utils.dart';
+import 'Socket.dart' as Socket;
 import 'Timers.dart';
+import 'Utils.dart';
+import 'WebSocketInterface.dart';
 import 'logger.dart';
 
 /**
@@ -159,11 +156,12 @@ class Transport {
     this.ondisconnect({'socket': this.socket, 'error': false});
   }
 
-  send(data) {
+  bool send(data) {
     debug('send()');
 
     if (!this.isConnected()) {
-      debugerror('unable to send message, transport is not connected. Current state is ${this.status}');
+      debugerror(
+          'unable to send message, transport is not connected. Current state is ${this.status}');
       return false;
     }
 
@@ -172,11 +170,11 @@ class Transport {
     return this.socket.send(message);
   }
 
-  isConnected() {
+  bool isConnected() {
     return this.status == C.STATUS_CONNECTED;
   }
 
-  isConnecting() {
+  bool isConnecting() {
     return this.status == C.STATUS_CONNECTING;
   }
 
diff --git a/lib/src/UA.dart b/lib/src/UA.dart
index f1dc21b4..1f8aca3c 100644
--- a/lib/src/UA.dart
+++ b/lib/src/UA.dart
@@ -1,11 +1,4 @@
 import 'package:events2/events2.dart';
-import 'package:sip_ua/src/SIPMessage.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/invite_client.dart';
-import 'package:sip_ua/src/transactions/invite_server.dart';
-import 'package:sip_ua/src/transactions/non_invite_client.dart';
-import 'package:sip_ua/src/transactions/non_invite_server.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
 
 import 'Config.dart' as config;
 import 'Config.dart';
@@ -17,6 +10,7 @@ import 'Message.dart';
 import 'Parser.dart' as Parser;
 import 'RTCSession.dart';
 import 'Registrator.dart';
+import 'SIPMessage.dart';
 import 'SIPMessage.dart' as SIPMessage;
 import 'Timers.dart';
 import 'Transport.dart';
@@ -24,6 +18,12 @@ import 'URI.dart';
 import 'Utils.dart' as Utils;
 import 'logger.dart';
 import 'sanityCheck.dart';
+import 'transactions/Transactions.dart';
+import 'transactions/invite_client.dart';
+import 'transactions/invite_server.dart';
+import 'transactions/non_invite_client.dart';
+import 'transactions/non_invite_server.dart';
+import 'transactions/transaction_base.dart';
 
 class C {
   // UA status codes.
@@ -217,14 +217,14 @@ class UA extends EventEmitter {
   /**
    * Registration state.
    */
-  isRegistered() {
+  bool isRegistered() {
     return this._registrator.registered;
   }
 
   /**
    * Connection state.
    */
-  isConnected() {
+  bool isConnected() {
     return this._transport.isConnected();
   }
 
@@ -237,9 +237,9 @@ class UA extends EventEmitter {
    * -throws {TypeError}
    *
    */
-  call(target, options) {
+  RTCSession call(target, options) {
     debug('call()');
-    var session = new RTCSession(this);
+    RTCSession session = new RTCSession(this);
     session.connect(target, options);
     return session;
   }
@@ -254,7 +254,8 @@ class UA extends EventEmitter {
    * -throws {TypeError}
    *
    */
-  sendMessage(target, body, options) {
+  Message sendMessage(
+      String target, String body, Map<String, dynamic> options) {
     debug('sendMessage()');
     var message = new Message(this);
     message.send(target, body, options);
@@ -264,7 +265,7 @@ class UA extends EventEmitter {
   /**
    * Terminate ongoing sessions.
    */
-  terminateSessions(options) {
+  void terminateSessions(Map<String, Object> options) {
     debug('terminateSessions()');
     this._sessions.forEach((idx, value) {
       if (!this._sessions[idx].isEnded()) {
@@ -469,7 +470,7 @@ class UA extends EventEmitter {
   /**
    * Unregistered
    */
-  unregistered(data) {
+  unregistered(Map<String, dynamic> data) {
     this.emit('unregistered', data);
   }
 
@@ -821,13 +822,13 @@ class UA extends EventEmitter {
  */
 
 // Transport connecting event.
-  onTransportConnecting(data) {
+  onTransportConnecting(Map<String, dynamic> data) {
     debug('Transport connecting');
     this.emit('connecting', data);
   }
 
 // Transport connected event.
-  onTransportConnect(data) {
+  onTransportConnect(Map<String, dynamic> data) {
     debug('Transport connected');
     if (this._status == C.STATUS_USER_CLOSED) {
       return;
@@ -843,7 +844,7 @@ class UA extends EventEmitter {
   }
 
 // Transport disconnected event.
-  onTransportDisconnect(data) {
+  onTransportDisconnect(Map<String, dynamic> data) {
     // Run _onTransportError_ callback on every client transaction using _transport_.
     this._transactions.removeAll().forEach((transaction) {
       transaction.onTransportError();
@@ -861,7 +862,7 @@ class UA extends EventEmitter {
   }
 
 // Transport data event.
-  onTransportData(data) {
+  onTransportData(Map<String, dynamic> data) {
     var transport = data['transport'];
     String messageData = data['message'];
 
diff --git a/lib/src/WebSocketInterface.dart b/lib/src/WebSocketInterface.dart
index f51207a8..efd62ef3 100644
--- a/lib/src/WebSocketInterface.dart
+++ b/lib/src/WebSocketInterface.dart
@@ -3,11 +3,10 @@ import 'dart:async';
 import 'dart:io';
 import 'dart:math';
 
-import 'package:sip_ua/src/Timers.dart';
-
+import 'Grammar.dart';
 import 'Socket.dart';
+import 'Timers.dart';
 import 'logger.dart';
-import 'Grammar.dart';
 
 class WebSocketInterface implements Socket {
   String _url;
@@ -18,7 +17,7 @@ class WebSocketInterface implements Socket {
   var _closed = false;
   var _connected = false;
   var weight;
-  var _wsExtraHeaders;
+  Map<String, dynamic> _wsExtraHeaders;
 
   final logger = Logger('WebSocketInterface');
   debug(msg) => logger.debug(msg);
@@ -30,7 +29,7 @@ class WebSocketInterface implements Socket {
   @override
   dynamic ondata;
 
-  WebSocketInterface(url, [wsExtraHeaders]) {
+  WebSocketInterface(String url, [Map<String, dynamic> wsExtraHeaders]) {
     debug('new() [url:' + url + ']');
     this._url = url;
     var parsed_url = Grammar.parse(url, 'absoluteURI');
@@ -160,7 +159,7 @@ class WebSocketInterface implements Socket {
   }
 
   @override
-  send(message) {
+  bool send(message) {
     debug('send()');
     if (this._closed) {
       throw 'transport closed';
diff --git a/lib/src/sanityCheck.dart b/lib/src/sanityCheck.dart
index b557bfda..1107b725 100644
--- a/lib/src/sanityCheck.dart
+++ b/lib/src/sanityCheck.dart
@@ -1,14 +1,13 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/SIPMessage.dart';
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/transactions/invite_server.dart';
-import 'package:sip_ua/src/transactions/non_invite_server.dart';
-
+import '../sip_ua.dart';
 import 'Constants.dart' as DartSIP_C;
 import 'Constants.dart';
+import 'SIPMessage.dart';
 import 'SIPMessage.dart' as SIPMessage;
+import 'Transport.dart';
 import 'Utils.dart' as Utils;
 import 'logger.dart';
+import 'transactions/invite_server.dart';
+import 'transactions/non_invite_server.dart';
 
 final logger = Logger('sanityCheck');
 debug(msg) => logger.debug(msg);
diff --git a/lib/src/transactions/Transactions.dart b/lib/src/transactions/Transactions.dart
index 55e022a8..e75b1dce 100644
--- a/lib/src/transactions/Transactions.dart
+++ b/lib/src/transactions/Transactions.dart
@@ -1,10 +1,8 @@
-import 'package:events2/events2.dart';
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Constants.dart';
-import 'package:sip_ua/src/Timers.dart';
-import 'package:sip_ua/src/transactions/invite_server.dart';
-import 'package:sip_ua/src/transactions/non_invite_server.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
+import '../Constants.dart';
+import '../Timers.dart';
+import 'invite_server.dart';
+import 'non_invite_server.dart';
+import 'transaction_base.dart';
 
 class TransactionBag {
   Map<String, TransactionBase> transactions = {};
diff --git a/lib/src/transactions/ack_client.dart b/lib/src/transactions/ack_client.dart
index e1cf19aa..d30ad93d 100644
--- a/lib/src/transactions/ack_client.dart
+++ b/lib/src/transactions/ack_client.dart
@@ -1,8 +1,7 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/Utils.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
+import '../../sip_ua.dart';
+import '../Transport.dart';
+import '../Utils.dart';
+import 'transaction_base.dart';
 
 final act_logger = new Logger('AckClientTransaction');
 debugact(msg) => act_logger.debug(msg);
diff --git a/lib/src/transactions/invite_client.dart b/lib/src/transactions/invite_client.dart
index ec915ec9..2ffa318a 100644
--- a/lib/src/transactions/invite_client.dart
+++ b/lib/src/transactions/invite_client.dart
@@ -1,12 +1,10 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Constants.dart';
-import 'package:sip_ua/src/Timers.dart';
-
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/Utils.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
+import '../../sip_ua.dart';
+import '../Constants.dart';
 import '../SIPMessage.dart' as SIPMessage;
+import '../Timers.dart';
+import '../Transport.dart';
+import '../Utils.dart';
+import 'transaction_base.dart';
 
 
 final ict_logger = new Logger('InviteClientTransaction');
diff --git a/lib/src/transactions/invite_server.dart b/lib/src/transactions/invite_server.dart
index d2593f2e..0d0b814b 100644
--- a/lib/src/transactions/invite_server.dart
+++ b/lib/src/transactions/invite_server.dart
@@ -1,8 +1,7 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Timers.dart';
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
+import '../../sip_ua.dart';
+import '../Timers.dart';
+import '../Transport.dart';
+import 'transaction_base.dart';
 
 final ist_logger = new Logger('InviteServerTransaction');
 debugist(msg) => ist_logger.debug(msg);
diff --git a/lib/src/transactions/non_invite_client.dart b/lib/src/transactions/non_invite_client.dart
index 5f9952cc..1f5dbf5d 100644
--- a/lib/src/transactions/non_invite_client.dart
+++ b/lib/src/transactions/non_invite_client.dart
@@ -1,11 +1,9 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Timers.dart';
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/Utils.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
-
+import '../../sip_ua.dart';
 import '../SIPMessage.dart' as SIPMessage;
+import '../Timers.dart';
+import '../Transport.dart';
+import '../Utils.dart';
+import 'transaction_base.dart';
 
 final nict_logger = new Logger('NonInviteClientTransaction');
 debugnict(msg) => nict_logger.debug(msg);
diff --git a/lib/src/transactions/non_invite_server.dart b/lib/src/transactions/non_invite_server.dart
index 70620313..9eefb8b0 100644
--- a/lib/src/transactions/non_invite_server.dart
+++ b/lib/src/transactions/non_invite_server.dart
@@ -1,9 +1,7 @@
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Timers.dart';
-
-import 'package:sip_ua/src/Transport.dart';
-import 'package:sip_ua/src/transactions/Transactions.dart';
-import 'package:sip_ua/src/transactions/transaction_base.dart';
+import '../../sip_ua.dart';
+import '../Timers.dart';
+import '../Transport.dart';
+import 'transaction_base.dart';
 
 final nist_logger = new Logger('NonInviteServerTransaction');
 debugnist(msg) => nist_logger.debug(msg);
diff --git a/lib/src/transactions/transaction_base.dart b/lib/src/transactions/transaction_base.dart
index d796ebeb..0bb461b5 100644
--- a/lib/src/transactions/transaction_base.dart
+++ b/lib/src/transactions/transaction_base.dart
@@ -1,6 +1,7 @@
 import 'package:events2/events2.dart';
-import 'package:sip_ua/sip_ua.dart';
-import 'package:sip_ua/src/Transport.dart';
+
+import '../../sip_ua.dart';
+import '../Transport.dart';
 
 enum TransactionState {
   // Transaction states.