diff --git a/Build/MQTTnet.nuspec b/Build/MQTTnet.nuspec
index 3687879..a905b00 100644
--- a/Build/MQTTnet.nuspec
+++ b/Build/MQTTnet.nuspec
@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>MQTTnet</id>
-    <version>2.1.5</version>
+    <version>2.2.0</version>
     <authors>Christian Kratky</authors>
     <owners>Christian Kratky</owners>
     <licenseUrl>https://github.com/chkr1011/MQTTnet/blob/master/LICENSE</licenseUrl>
@@ -10,14 +10,14 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>MQTTnet is a .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
-    <releaseNotes>* [MqttServer] Added support for publishing application messages
-* [Core] Fixed QoS level 2 handling
-* [Core] Performance optimizations
-* [MqttClient/MqttServer] Errors while handline application messages are now catched and traced
-* [MqttClient/MqttServer] Added interfaces
+    <releaseNotes>* [Server] Added support for MQTT protocol version 3.1.0
+* [Server] Providing the used protocol version of connected clients
+* [Client] Added support for protocol version 3.1.0
+* [Core] Several minor performance improvements
+* [Core] Fixed an issue with connection management (Thanks to wuzhenda; Zuendelmeister)
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2017</copyright>
-    <tags>MQTT MQTTClient MQTTServer MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Queue Hardware</tags> 
+    <tags>MQTT MQTTClient MQTTServer MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Queue Hardware Arduino</tags> 
     <dependencies>
 
       <group targetFramework="netstandard1.3">
diff --git a/Frameworks/MQTTnet.NetFramework/Implementations/MqttServerAdapter.cs b/Frameworks/MQTTnet.NetFramework/Implementations/MqttServerAdapter.cs
index cbfcf66..63fd0d8 100644
--- a/Frameworks/MQTTnet.NetFramework/Implementations/MqttServerAdapter.cs
+++ b/Frameworks/MQTTnet.NetFramework/Implementations/MqttServerAdapter.cs
@@ -86,7 +86,7 @@ namespace MQTTnet.Implementations
                 try
                 {
                     var clientSocket = await Task.Factory.FromAsync(_defaultEndpointSocket.BeginAccept, _defaultEndpointSocket.EndAccept, null);
-                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new DefaultMqttV311PacketSerializer());
+                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new MqttPacketSerializer());
                     ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                 }
                 catch (Exception exception) when (!(exception is ObjectDisposedException))
@@ -107,7 +107,7 @@ namespace MQTTnet.Implementations
                     var sslStream = new SslStream(new NetworkStream(clientSocket));
                     await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, SslProtocols.Tls12, false);
                     
-                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new DefaultMqttV311PacketSerializer());
+                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new MqttPacketSerializer());
                     ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                 }
                 catch (Exception exception)
diff --git a/Frameworks/MQTTnet.NetFramework/Implementations/MqttTcpChannel.cs b/Frameworks/MQTTnet.NetFramework/Implementations/MqttTcpChannel.cs
index 3a43a3e..c9c080d 100644
--- a/Frameworks/MQTTnet.NetFramework/Implementations/MqttTcpChannel.cs
+++ b/Frameworks/MQTTnet.NetFramework/Implementations/MqttTcpChannel.cs
@@ -12,12 +12,11 @@ namespace MQTTnet.Implementations
 {
     public sealed class MqttTcpChannel : IMqttCommunicationChannel, IDisposable
     {
-        private readonly Socket _socket;
+        private Socket _socket;
         private SslStream _sslStream;
 
         public MqttTcpChannel()
         {
-            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
         }
 
         public MqttTcpChannel(Socket socket, SslStream sslStream)
@@ -31,6 +30,11 @@ namespace MQTTnet.Implementations
             if (options == null) throw new ArgumentNullException(nameof(options));
             try
             {
+                if (_socket == null)
+                {
+                    _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+                }
+
                 await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, options.Server, options.GetPort(), null);
 
                 if (options.TlsOptions.UseTls)
@@ -49,8 +53,7 @@ namespace MQTTnet.Implementations
         {
             try
             {
-                _sslStream.Dispose();
-                _socket.Dispose();
+                Dispose();
                 return Task.FromResult(0);
             }
             catch (SocketException exception)
@@ -108,6 +111,9 @@ namespace MQTTnet.Implementations
         {
             _socket?.Dispose();
             _sslStream?.Dispose();
+
+            _socket = null;
+            _sslStream = null;
         }
 
         private static X509CertificateCollection LoadCertificates(MqttClientOptions options)
diff --git a/Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs b/Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs
index ac12f97..7dd7500 100644
--- a/Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs
+++ b/Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs
@@ -12,7 +12,7 @@ namespace MQTTnet
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new MqttPacketSerializer()));
         }
     }
 }
\ No newline at end of file
diff --git a/Frameworks/MQTTnet.NetFramework/Properties/AssemblyInfo.cs b/Frameworks/MQTTnet.NetFramework/Properties/AssemblyInfo.cs
index 4d0a57f..486eca7 100644
--- a/Frameworks/MQTTnet.NetFramework/Properties/AssemblyInfo.cs
+++ b/Frameworks/MQTTnet.NetFramework/Properties/AssemblyInfo.cs
@@ -11,5 +11,5 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
 [assembly: Guid("a480ef90-0eaa-4d9a-b271-47a9c47f6f7d")]
-[assembly: AssemblyVersion("2.1.4.0")]
-[assembly: AssemblyFileVersion("2.1.4.0")]
\ No newline at end of file
+[assembly: AssemblyVersion("2.1.5.1")]
+[assembly: AssemblyFileVersion("2.1.5.1")]
\ No newline at end of file
diff --git a/Frameworks/MQTTnet.NetStandard/Implementations/MqttServerAdapter.cs b/Frameworks/MQTTnet.NetStandard/Implementations/MqttServerAdapter.cs
index 863d3e7..a2e86b1 100644
--- a/Frameworks/MQTTnet.NetStandard/Implementations/MqttServerAdapter.cs
+++ b/Frameworks/MQTTnet.NetStandard/Implementations/MqttServerAdapter.cs
@@ -84,7 +84,7 @@ namespace MQTTnet.Implementations
                 try
                 {
                     var clientSocket = await _defaultEndpointSocket.AcceptAsync();
-                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new DefaultMqttV311PacketSerializer());
+                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new MqttPacketSerializer());
                     ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                 }
                 catch (Exception exception)
@@ -105,7 +105,7 @@ namespace MQTTnet.Implementations
                     var sslStream = new SslStream(new NetworkStream(clientSocket));
                     await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, SslProtocols.Tls12, false);
                     
-                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new DefaultMqttV311PacketSerializer());
+                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new MqttPacketSerializer());
                     ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                 }
                 catch (Exception exception)
diff --git a/Frameworks/MQTTnet.NetStandard/Implementations/MqttTcpChannel.cs b/Frameworks/MQTTnet.NetStandard/Implementations/MqttTcpChannel.cs
index e78cd98..a4247b0 100644
--- a/Frameworks/MQTTnet.NetStandard/Implementations/MqttTcpChannel.cs
+++ b/Frameworks/MQTTnet.NetStandard/Implementations/MqttTcpChannel.cs
@@ -12,12 +12,11 @@ namespace MQTTnet.Implementations
 {
     public sealed class MqttTcpChannel : IMqttCommunicationChannel, IDisposable
     {
-        private readonly Socket _socket;
+        private Socket _socket;
         private SslStream _sslStream;
 
         public MqttTcpChannel()
         {
-            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
         }
 
         public MqttTcpChannel(Socket socket, SslStream sslStream)
@@ -31,6 +30,11 @@ namespace MQTTnet.Implementations
             if (options == null) throw new ArgumentNullException(nameof(options));
             try
             {
+                if (_socket == null)
+                {
+                    _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+                }
+
                 await _socket.ConnectAsync(options.Server, options.GetPort());
                 
                 if (options.TlsOptions.UseTls)
@@ -49,8 +53,7 @@ namespace MQTTnet.Implementations
         {
             try
             {
-                _sslStream.Dispose();
-                _socket.Dispose();
+                Dispose();
                 return Task.FromResult(0);
             }
             catch (SocketException exception)
@@ -101,6 +104,9 @@ namespace MQTTnet.Implementations
         {
             _socket?.Dispose();
             _sslStream?.Dispose();
+
+            _socket = null;
+            _sslStream = null;
         }
 
         private static X509CertificateCollection LoadCertificates(MqttClientOptions options)
diff --git a/Frameworks/MQTTnet.NetStandard/MQTTnet.Netstandard.csproj b/Frameworks/MQTTnet.NetStandard/MQTTnet.Netstandard.csproj
index 2a60e55..1a1249e 100644
--- a/Frameworks/MQTTnet.NetStandard/MQTTnet.Netstandard.csproj
+++ b/Frameworks/MQTTnet.NetStandard/MQTTnet.Netstandard.csproj
@@ -4,8 +4,8 @@
     <TargetFramework>netstandard1.3</TargetFramework>
     <AssemblyName>MQTTnet</AssemblyName>
     <RootNamespace>MQTTnet</RootNamespace>
-    <AssemblyVersion>2.1.4.0</AssemblyVersion>
-    <FileVersion>2.1.4.0</FileVersion>
+    <AssemblyVersion>2.1.5.1</AssemblyVersion>
+    <FileVersion>2.1.5.1</FileVersion>
     <Version>0.0.0.0</Version>
     <Company />
     <Product />
diff --git a/Frameworks/MQTTnet.NetStandard/MqttClientFactory.cs b/Frameworks/MQTTnet.NetStandard/MqttClientFactory.cs
index 6073583..f47c494 100644
--- a/Frameworks/MQTTnet.NetStandard/MqttClientFactory.cs
+++ b/Frameworks/MQTTnet.NetStandard/MqttClientFactory.cs
@@ -12,7 +12,7 @@ namespace MQTTnet
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new MqttPacketSerializer()));
         }
     }
 }
diff --git a/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttServerAdapter.cs b/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttServerAdapter.cs
index ea251ca..eddd671 100644
--- a/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttServerAdapter.cs
+++ b/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttServerAdapter.cs
@@ -52,7 +52,7 @@ namespace MQTTnet.Implementations
         {
             try
             {
-                var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(args.Socket), new DefaultMqttV311PacketSerializer());
+                var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(args.Socket), new MqttPacketSerializer());
                 ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(args.Socket.Information.RemoteAddress.ToString(), clientAdapter));
             }
             catch (Exception exception)
diff --git a/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttTcpChannel.cs b/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttTcpChannel.cs
index 99681b7..482ce32 100644
--- a/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttTcpChannel.cs
+++ b/Frameworks/MQTTnet.UniversalWindows/Implementations/MqttTcpChannel.cs
@@ -15,11 +15,10 @@ namespace MQTTnet.Implementations
 {
     public sealed class MqttTcpChannel : IMqttCommunicationChannel, IDisposable
     {
-        private readonly StreamSocket _socket;
+        private StreamSocket _socket;
 
         public MqttTcpChannel()
         {
-            _socket = new StreamSocket();
         }
 
         public MqttTcpChannel(StreamSocket socket)
@@ -32,6 +31,11 @@ namespace MQTTnet.Implementations
             if (options == null) throw new ArgumentNullException(nameof(options));
             try
             {
+                if (_socket == null)
+                {
+                    _socket = new StreamSocket();
+                }
+
                 if (!options.TlsOptions.UseTls)
                 {
                     await _socket.ConnectAsync(new HostName(options.Server), options.GetPort().ToString());
@@ -59,7 +63,7 @@ namespace MQTTnet.Implementations
         {
             try
             {
-                _socket.Dispose();
+                Dispose();
                 return Task.FromResult(0);
             }
             catch (SocketException exception)
@@ -100,6 +104,8 @@ namespace MQTTnet.Implementations
         public void Dispose()
         {
             _socket?.Dispose();
+
+            _socket = null;
         }
 
         private static Certificate LoadCertificate(MqttClientOptions options)
diff --git a/Frameworks/MQTTnet.UniversalWindows/MqttClientFactory.cs b/Frameworks/MQTTnet.UniversalWindows/MqttClientFactory.cs
index ac12f97..7dd7500 100644
--- a/Frameworks/MQTTnet.UniversalWindows/MqttClientFactory.cs
+++ b/Frameworks/MQTTnet.UniversalWindows/MqttClientFactory.cs
@@ -12,7 +12,7 @@ namespace MQTTnet
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new MqttPacketSerializer()));
         }
     }
 }
\ No newline at end of file
diff --git a/Frameworks/MQTTnet.UniversalWindows/Properties/AssemblyInfo.cs b/Frameworks/MQTTnet.UniversalWindows/Properties/AssemblyInfo.cs
index dee61f7..05204eb 100644
--- a/Frameworks/MQTTnet.UniversalWindows/Properties/AssemblyInfo.cs
+++ b/Frameworks/MQTTnet.UniversalWindows/Properties/AssemblyInfo.cs
@@ -10,5 +10,5 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
-[assembly: AssemblyVersion("2.1.4.0")]
-[assembly: AssemblyFileVersion("2.1.4.0")]
\ No newline at end of file
+[assembly: AssemblyVersion("2.1.5.1")]
+[assembly: AssemblyFileVersion("2.1.5.1")]
\ No newline at end of file
diff --git a/MQTTnet.Core/Adapter/IMqttCommunicationAdapter.cs b/MQTTnet.Core/Adapter/IMqttCommunicationAdapter.cs
index 6651e05..77ab898 100644
--- a/MQTTnet.Core/Adapter/IMqttCommunicationAdapter.cs
+++ b/MQTTnet.Core/Adapter/IMqttCommunicationAdapter.cs
@@ -2,6 +2,7 @@
 using System.Threading.Tasks;
 using MQTTnet.Core.Client;
 using MQTTnet.Core.Packets;
+using MQTTnet.Core.Serializer;
 
 namespace MQTTnet.Core.Adapter
 {
@@ -14,5 +15,7 @@ namespace MQTTnet.Core.Adapter
         Task SendPacketAsync(MqttBasePacket packet, TimeSpan timeout);
 
         Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout);
+
+        IMqttPacketSerializer PacketSerializer { get; }
     }
 }
diff --git a/MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs b/MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs
index ae90984..04b5ca7 100644
--- a/MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs
+++ b/MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs
@@ -11,22 +11,19 @@ namespace MQTTnet.Core.Adapter
 {
     public class MqttChannelCommunicationAdapter : IMqttCommunicationAdapter
     {
-        private readonly IMqttPacketSerializer _serializer;
         private readonly IMqttCommunicationChannel _channel;
 
         public MqttChannelCommunicationAdapter(IMqttCommunicationChannel channel, IMqttPacketSerializer serializer)
         {
             _channel = channel ?? throw new ArgumentNullException(nameof(channel));
-            _serializer = serializer ?? throw new ArgumentNullException(nameof(serializer));
+            PacketSerializer = serializer ?? throw new ArgumentNullException(nameof(serializer));
         }
 
+        public IMqttPacketSerializer PacketSerializer { get; }
+
         public async Task ConnectAsync(MqttClientOptions options, TimeSpan timeout)
         {
-            var task = _channel.ConnectAsync(options);
-            if (await Task.WhenAny(Task.Delay(timeout), task) != task)
-            {
-                throw new MqttCommunicationTimedOutException();
-            }
+            await ExecuteWithTimeoutAsync(_channel.ConnectAsync(options), timeout);
         }
 
         public async Task DisconnectAsync()
@@ -38,21 +35,7 @@ namespace MQTTnet.Core.Adapter
         {
             MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"TX >>> {packet} [Timeout={timeout}]");
 
-            bool hasTimeout;
-            try
-            {
-                var task = _serializer.SerializeAsync(packet, _channel);
-                hasTimeout = await Task.WhenAny(Task.Delay(timeout), task) != task;
-            }
-            catch (Exception exception)
-            {
-                throw new MqttCommunicationException(exception);
-            }
-
-            if (hasTimeout)
-            {
-                throw new MqttCommunicationTimedOutException();
-            }
+            await ExecuteWithTimeoutAsync(PacketSerializer.SerializeAsync(packet, _channel), timeout);
         }
 
         public async Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout)
@@ -60,20 +43,11 @@ namespace MQTTnet.Core.Adapter
             MqttBasePacket packet;
             if (timeout > TimeSpan.Zero)
             {
-                var workerTask = _serializer.DeserializeAsync(_channel);
-                var timeoutTask = Task.Delay(timeout);
-                var hasTimeout = Task.WhenAny(timeoutTask, workerTask) == timeoutTask;
-
-                if (hasTimeout)
-                {
-                    throw new MqttCommunicationTimedOutException();
-                }
-
-                packet = workerTask.Result;
+                packet = await ExecuteWithTimeoutAsync(PacketSerializer.DeserializeAsync(_channel), timeout);
             }
             else
             {
-                packet = await _serializer.DeserializeAsync(_channel);
+                packet = await PacketSerializer.DeserializeAsync(_channel);
             }
 
             if (packet == null)
@@ -84,5 +58,35 @@ namespace MQTTnet.Core.Adapter
             MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"RX <<< {packet}");
             return packet;
         }
+
+        private static async Task<TResult> ExecuteWithTimeoutAsync<TResult>(Task<TResult> task, TimeSpan timeout)
+        {
+            var timeoutTask = Task.Delay(timeout);
+            if (await Task.WhenAny(timeoutTask, task) == timeoutTask)
+            {
+                throw new MqttCommunicationTimedOutException();
+            }
+
+            if (task.IsFaulted)
+            {
+                throw new MqttCommunicationException(task.Exception);
+            }
+
+            return task.Result;
+        }
+
+        private static async Task ExecuteWithTimeoutAsync(Task task, TimeSpan timeout)
+        {
+            var timeoutTask = Task.Delay(timeout);
+            if (await Task.WhenAny(timeoutTask, task) == timeoutTask)
+            {
+                throw new MqttCommunicationTimedOutException();
+            }
+
+            if (task.IsFaulted)
+            {
+                throw new MqttCommunicationException(task.Exception);
+            }
+        }
     }
 }
\ No newline at end of file
diff --git a/MQTTnet.Core/Client/MqttClient.cs b/MQTTnet.Core/Client/MqttClient.cs
index 384de1f..3481cbe 100644
--- a/MQTTnet.Core/Client/MqttClient.cs
+++ b/MQTTnet.Core/Client/MqttClient.cs
@@ -20,6 +20,7 @@ namespace MQTTnet.Core.Client
         private readonly MqttClientOptions _options;
         private readonly IMqttCommunicationAdapter _adapter;
 
+        private bool _disconnectedEventSuspended;
         private int _latestPacketIdentifier;
         private CancellationTokenSource _cancellationTokenSource;
 
@@ -27,6 +28,8 @@ namespace MQTTnet.Core.Client
         {
             _options = options ?? throw new ArgumentNullException(nameof(options));
             _adapter = adapter ?? throw new ArgumentNullException(nameof(adapter));
+
+            _adapter.PacketSerializer.ProtocolVersion = options.ProtocolVersion;
         }
 
         public event EventHandler Connected;
@@ -46,49 +49,64 @@ namespace MQTTnet.Core.Client
                 throw new MqttProtocolViolationException("It is not allowed to connect with a server after the connection is established.");
             }
 
-            var connectPacket = new MqttConnectPacket
+            try
             {
-                ClientId = _options.ClientId,
-                Username = _options.UserName,
-                Password = _options.Password,
-                CleanSession = _options.CleanSession,
-                KeepAlivePeriod = (ushort)_options.KeepAlivePeriod.TotalSeconds,
-                WillMessage = willApplicationMessage
-            };
+                _disconnectedEventSuspended = false;
 
-            await _adapter.ConnectAsync(_options, _options.DefaultCommunicationTimeout);
-            MqttTrace.Verbose(nameof(MqttClient), "Connection with server established.");
+                await _adapter.ConnectAsync(_options, _options.DefaultCommunicationTimeout);
 
-            _cancellationTokenSource = new CancellationTokenSource();
-            _latestPacketIdentifier = 0;
-            _packetDispatcher.Reset();
-            IsConnected = true;
+                MqttTrace.Verbose(nameof(MqttClient), "Connection with server established.");
 
-#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-            Task.Run(() => ReceivePackets(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
-#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                var connectPacket = new MqttConnectPacket
+                {
+                    ClientId = _options.ClientId,
+                    Username = _options.UserName,
+                    Password = _options.Password,
+                    CleanSession = _options.CleanSession,
+                    KeepAlivePeriod = (ushort)_options.KeepAlivePeriod.TotalSeconds,
+                    WillMessage = willApplicationMessage
+                };
+
+                _cancellationTokenSource = new CancellationTokenSource();
+                _latestPacketIdentifier = 0;
+                _packetDispatcher.Reset();
+
+                StartReceivePackets();
+
+                var response = await SendAndReceiveAsync<MqttConnAckPacket>(connectPacket);
+                if (response.ConnectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
+                {
+                    await DisconnectInternalAsync();
+                    throw new MqttConnectingFailedException(response.ConnectReturnCode);
+                }
 
-            var response = await SendAndReceiveAsync<MqttConnAckPacket>(connectPacket);
-            if (response.ConnectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
-            {
-                await DisconnectAsync();
-                throw new MqttConnectingFailedException(response.ConnectReturnCode);
-            }
+                if (_options.KeepAlivePeriod != TimeSpan.Zero)
+                {
+                    StartSendKeepAliveMessages();
+                }
+
+                MqttTrace.Verbose(nameof(MqttClient), "MQTT connection with server established.");
 
-            if (_options.KeepAlivePeriod != TimeSpan.Zero)
+                IsConnected = true;
+                Connected?.Invoke(this, EventArgs.Empty);
+            }
+            catch (Exception)
             {
-#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-                Task.Run(() => SendKeepAliveMessagesAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
-#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                await DisconnectInternalAsync();
+                throw;
             }
-
-            Connected?.Invoke(this, EventArgs.Empty);
         }
 
         public async Task DisconnectAsync()
         {
-            await SendAsync(new MqttDisconnectPacket());
-            await DisconnectInternalAsync();
+            try
+            {
+                await SendAsync(new MqttDisconnectPacket());
+            }
+            finally
+            {
+                await DisconnectInternalAsync();
+            }
         }
 
         public Task<IList<MqttSubscribeResult>> SubscribeAsync(params TopicFilter[] topicFilters)
@@ -179,8 +197,9 @@ namespace MQTTnet.Core.Client
             {
                 await _adapter.DisconnectAsync();
             }
-            catch
+            catch (Exception exception)
             {
+                MqttTrace.Warning(nameof(MqttClient), exception, "Error while disconnecting.");
             }
             finally
             {
@@ -189,7 +208,12 @@ namespace MQTTnet.Core.Client
                 _cancellationTokenSource = null;
 
                 IsConnected = false;
-                Disconnected?.Invoke(this, EventArgs.Empty);
+
+                if (!_disconnectedEventSuspended)
+                {
+                    _disconnectedEventSuspended = true;
+                    Disconnected?.Invoke(this, EventArgs.Empty);
+                }
             }
         }
 
@@ -237,7 +261,7 @@ namespace MQTTnet.Core.Client
             }
             catch (Exception exception)
             {
-                MqttTrace.Error(nameof(MqttClient), exception, "Unhandled exception while handling application message.");    
+                MqttTrace.Error(nameof(MqttClient), exception, "Unhandled exception while handling application message.");
             }
         }
 
@@ -267,7 +291,7 @@ namespace MQTTnet.Core.Client
                 return SendAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier });
             }
 
-            throw new InvalidOperationException();
+            throw new MqttCommunicationException("Received a not supported QoS level.");
         }
 
         private async Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket)
@@ -276,7 +300,7 @@ namespace MQTTnet.Core.Client
             {
                 _unacknowledgedPublishPackets.Remove(pubRelPacket.PacketIdentifier);
             }
-            
+
             await SendAsync(pubRelPacket.CreateResponse<MqttPubCompPacket>());
         }
 
@@ -298,15 +322,12 @@ namespace MQTTnet.Core.Client
                 var pi1 = requestPacket as IMqttPacketWithIdentifier;
                 var pi2 = p as IMqttPacketWithIdentifier;
 
-                if (pi1 != null && pi2 != null)
+                if (pi1 == null || pi2 == null)
                 {
-                    if (pi1.PacketIdentifier != pi2.PacketIdentifier)
-                    {
-                        return false;
-                    }
+                    return true;
                 }
 
-                return true;
+                return pi1.PacketIdentifier == pi2.PacketIdentifier;
             }
 
             await _adapter.SendPacketAsync(requestPacket, _options.DefaultCommunicationTimeout);
@@ -333,15 +354,16 @@ namespace MQTTnet.Core.Client
             catch (MqttCommunicationException exception)
             {
                 MqttTrace.Warning(nameof(MqttClient), exception, "MQTT communication error while receiving packets.");
+                await DisconnectInternalAsync();
             }
             catch (Exception exception)
             {
                 MqttTrace.Warning(nameof(MqttClient), exception, "Error while sending/receiving keep alive packets.");
+                await DisconnectInternalAsync();
             }
             finally
             {
                 MqttTrace.Information(nameof(MqttClient), "Stopped sending keep alive packets.");
-                await DisconnectInternalAsync();
             }
         }
 
@@ -352,27 +374,47 @@ namespace MQTTnet.Core.Client
             {
                 while (!cancellationToken.IsCancellationRequested)
                 {
-                    var mqttPacket = await _adapter.ReceivePacketAsync(TimeSpan.Zero);
-                    MqttTrace.Information(nameof(MqttClient), $"Received <<< {mqttPacket}");
+                    var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero);
+                    MqttTrace.Information(nameof(MqttClient), $"Received <<< {packet}");
 
-#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-                    Task.Run(() => ProcessReceivedPacketAsync(mqttPacket), cancellationToken);
-#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                    StartProcessReceivedPacket(packet, cancellationToken);
                 }
             }
             catch (MqttCommunicationException exception)
             {
-                MqttTrace.Warning(nameof(MqttClient), exception, "MQTT communication error while receiving packets.");
+                MqttTrace.Warning(nameof(MqttClient), exception, "MQTT communication exception while receiving packets.");
+                await DisconnectInternalAsync();
             }
             catch (Exception exception)
             {
-                MqttTrace.Error(nameof(MqttClient), exception, "Error while receiving packets.");
+                MqttTrace.Error(nameof(MqttClient), exception, "Unhandled exception while receiving packets.");
+                await DisconnectInternalAsync();
             }
             finally
             {
                 MqttTrace.Information(nameof(MqttClient), "Stopped receiving packets.");
-                await DisconnectInternalAsync();
             }
         }
+
+        private void StartProcessReceivedPacket(MqttBasePacket packet, CancellationToken cancellationToken)
+        {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            Task.Run(() => ProcessReceivedPacketAsync(packet), cancellationToken);
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+        }
+
+        private void StartReceivePackets()
+        {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            Task.Run(() => ReceivePackets(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+        }
+
+        private void StartSendKeepAliveMessages()
+        {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            Task.Run(() => SendKeepAliveMessagesAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+        }
     }
 }
\ No newline at end of file
diff --git a/MQTTnet.Core/Client/MqttClientOptions.cs b/MQTTnet.Core/Client/MqttClientOptions.cs
index 0aaf43c..f9b75fa 100644
--- a/MQTTnet.Core/Client/MqttClientOptions.cs
+++ b/MQTTnet.Core/Client/MqttClientOptions.cs
@@ -1,4 +1,5 @@
 using System;
+using MQTTnet.Core.Serializer;
 
 namespace MQTTnet.Core.Client
 {
@@ -7,8 +8,8 @@ namespace MQTTnet.Core.Client
         public string Server { get; set; }
 
         public int? Port { get; set; }
-        
-        public MqttClientTlsOptions TlsOptions { get; } = new MqttClientTlsOptions();
+
+        public MqttClientTlsOptions TlsOptions { get; set; } = new MqttClientTlsOptions();
 
         public string UserName { get; set; }
 
@@ -21,5 +22,7 @@ namespace MQTTnet.Core.Client
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(5);
 
         public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
+
+        public MqttProtocolVersion ProtocolVersion { get; set; } = MqttProtocolVersion.V311;
     }
 }
diff --git a/MQTTnet.Core/Exceptions/MqttCommunicationException.cs b/MQTTnet.Core/Exceptions/MqttCommunicationException.cs
index 8b471a0..2fc578e 100644
--- a/MQTTnet.Core/Exceptions/MqttCommunicationException.cs
+++ b/MQTTnet.Core/Exceptions/MqttCommunicationException.cs
@@ -4,7 +4,7 @@ namespace MQTTnet.Core.Exceptions
 {
     public class MqttCommunicationException : Exception
     {
-        public MqttCommunicationException()
+        protected MqttCommunicationException()
         {
         }
 
@@ -17,5 +17,10 @@ namespace MQTTnet.Core.Exceptions
             : base(message)
         {
         }
+
+        public MqttCommunicationException(string message, Exception innerException)
+            : base(message, innerException)
+        {
+        }
     }
 }
diff --git a/MQTTnet.Core/MQTTnet.Core.csproj b/MQTTnet.Core/MQTTnet.Core.csproj
index 4d12864..c938551 100644
--- a/MQTTnet.Core/MQTTnet.Core.csproj
+++ b/MQTTnet.Core/MQTTnet.Core.csproj
@@ -16,8 +16,8 @@
     <PackageIconUrl></PackageIconUrl>
     <RepositoryUrl></RepositoryUrl>
     <PackageTags></PackageTags>
-    <FileVersion>2.1.4.0</FileVersion>
-    <AssemblyVersion>2.1.4.0</AssemblyVersion>
+    <FileVersion>2.1.5.1</FileVersion>
+    <AssemblyVersion>2.1.5.1</AssemblyVersion>
     <PackageLicenseUrl></PackageLicenseUrl>
   </PropertyGroup>
 
diff --git a/MQTTnet.Core/Packets/MqttConnectPacket.cs b/MQTTnet.Core/Packets/MqttConnectPacket.cs
index aadfe52..6db92a2 100644
--- a/MQTTnet.Core/Packets/MqttConnectPacket.cs
+++ b/MQTTnet.Core/Packets/MqttConnectPacket.cs
@@ -1,7 +1,11 @@
-namespace MQTTnet.Core.Packets
+using MQTTnet.Core.Serializer;
+
+namespace MQTTnet.Core.Packets
 {
     public sealed class MqttConnectPacket: MqttBasePacket
     {
+        public MqttProtocolVersion ProtocolVersion { get; set; }
+
         public string ClientId { get; set; }
 
         public string Username { get; set; }
diff --git a/MQTTnet.Core/Serializer/IMqttPacketSerializer.cs b/MQTTnet.Core/Serializer/IMqttPacketSerializer.cs
index db53a13..801b7ea 100644
--- a/MQTTnet.Core/Serializer/IMqttPacketSerializer.cs
+++ b/MQTTnet.Core/Serializer/IMqttPacketSerializer.cs
@@ -6,6 +6,8 @@ namespace MQTTnet.Core.Serializer
 {
     public interface IMqttPacketSerializer
     {
+        MqttProtocolVersion ProtocolVersion { get; set; }
+
         Task SerializeAsync(MqttBasePacket mqttPacket, IMqttCommunicationChannel destination);
 
         Task<MqttBasePacket> DeserializeAsync(IMqttCommunicationChannel source);
diff --git a/MQTTnet.Core/Serializer/MqttPacketReader.cs b/MQTTnet.Core/Serializer/MqttPacketReader.cs
index f59d807..9abea6d 100644
--- a/MQTTnet.Core/Serializer/MqttPacketReader.cs
+++ b/MQTTnet.Core/Serializer/MqttPacketReader.cs
@@ -10,7 +10,7 @@ namespace MQTTnet.Core.Serializer
 {
     public sealed class MqttPacketReader : IDisposable
     {
-        private readonly MemoryStream _remainingData = new MemoryStream();
+        private readonly MemoryStream _remainingData = new MemoryStream(1024);
         private readonly IMqttCommunicationChannel _source;
 
         private int _remainingLength;
diff --git a/MQTTnet.Core/Serializer/DefaultMqttV311PacketSerializer.cs b/MQTTnet.Core/Serializer/MqttPacketSerializer.cs
similarity index 92%
rename from MQTTnet.Core/Serializer/DefaultMqttV311PacketSerializer.cs
rename to MQTTnet.Core/Serializer/MqttPacketSerializer.cs
index 4100b6c..f9ec70c 100644
--- a/MQTTnet.Core/Serializer/DefaultMqttV311PacketSerializer.cs
+++ b/MQTTnet.Core/Serializer/MqttPacketSerializer.cs
@@ -9,8 +9,13 @@ using MQTTnet.Core.Protocol;
 
 namespace MQTTnet.Core.Serializer
 {
-    public sealed class DefaultMqttV311PacketSerializer : IMqttPacketSerializer
+    public sealed class MqttPacketSerializer : IMqttPacketSerializer
     {
+        private static byte[] ProtocolVersionV311Name { get; } = Encoding.UTF8.GetBytes("MQTT");
+        private static byte[] ProtocolVersionV310Name { get; } = Encoding.UTF8.GetBytes("MQIs");
+
+        public MqttProtocolVersion ProtocolVersion { get; set; } = MqttProtocolVersion.V311;
+
         public Task SerializeAsync(MqttBasePacket packet, IMqttCommunicationChannel destination)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
@@ -255,12 +260,21 @@ namespace MQTTnet.Core.Serializer
         private static async Task<MqttBasePacket> DeserializeConnectAsync(MqttPacketReader reader)
         {
             await reader.ReadRemainingDataAsync(2); // Skip 2 bytes
-            
-            var protocolName = await reader.ReadRemainingDataAsync(4);
 
-            if (Encoding.UTF8.GetString(protocolName, 0, protocolName.Length) != "MQTT")
+            MqttProtocolVersion protocolVersion;
+            var protocolName = await reader.ReadRemainingDataAsync(4);
+            if (protocolName.SequenceEqual(ProtocolVersionV310Name))
+            {
+                await reader.ReadRemainingDataAsync(2);
+                protocolVersion = MqttProtocolVersion.V310;
+            }
+            else if (protocolName.SequenceEqual(ProtocolVersionV311Name))
             {
-                throw new MqttProtocolViolationException("Protocol name is not 'MQTT'.");
+                protocolVersion = MqttProtocolVersion.V311;
+            }
+            else
+            {
+                throw new MqttProtocolViolationException("Protocol name is not supported.");
             }
 
             var protocolLevel = await reader.ReadRemainingDataByteAsync();
@@ -271,6 +285,7 @@ namespace MQTTnet.Core.Serializer
 
             var packet = new MqttConnectPacket
             {
+                ProtocolVersion = protocolVersion,
                 CleanSession = connectFlagsReader.Read()
             };
 
@@ -351,9 +366,7 @@ namespace MQTTnet.Core.Serializer
             }
         }
 
-        private static readonly byte[] MqttPrefix = Encoding.UTF8.GetBytes("MQTT");
-
-        private static Task SerializeAsync(MqttConnectPacket packet, IMqttCommunicationChannel destination)
+        private Task SerializeAsync(MqttConnectPacket packet, IMqttCommunicationChannel destination)
         {
             ValidateConnectPacket(packet);
 
@@ -361,9 +374,19 @@ namespace MQTTnet.Core.Serializer
             {
                 // Write variable header
                 output.Write(0x00, 0x04); // 3.1.2.1 Protocol Name
-                output.Write(MqttPrefix);
-                output.Write(0x04); // 3.1.2.2 Protocol Level
-
+                if (ProtocolVersion == MqttProtocolVersion.V311)
+                {
+                    output.Write(ProtocolVersionV311Name);
+                    output.Write(0x04); // 3.1.2.2 Protocol Level (4)
+                }
+                else
+                {
+                    output.Write(ProtocolVersionV310Name);
+                    output.Write(0x64);
+                    output.Write(0x70);
+                    output.Write(0x03); // Protocol Level (3)
+                }
+                
                 var connectFlags = new ByteWriter(); // 3.1.2.3 Connect Flags
                 connectFlags.Write(false); // Reserved
                 connectFlags.Write(packet.CleanSession);
@@ -408,13 +431,17 @@ namespace MQTTnet.Core.Serializer
             }
         }
 
-        private static Task SerializeAsync(MqttConnAckPacket packet, IMqttCommunicationChannel destination)
+        private Task SerializeAsync(MqttConnAckPacket packet, IMqttCommunicationChannel destination)
         {
             using (var output = new MqttPacketWriter())
             {
                 var connectAcknowledgeFlags = new ByteWriter();
-                connectAcknowledgeFlags.Write(packet.IsSessionPresent);
 
+                if (ProtocolVersion == MqttProtocolVersion.V311)
+                {
+                    connectAcknowledgeFlags.Write(packet.IsSessionPresent);
+                }
+                
                 output.Write(connectAcknowledgeFlags);
                 output.Write((byte)packet.ConnectReturnCode);
 
@@ -423,6 +450,17 @@ namespace MQTTnet.Core.Serializer
             }
         }
 
+        private static async Task SerializeAsync(MqttPubRelPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.PubRel, 0x02);
+                await output.WriteToAsync(destination);
+            }
+        }
+
         private static Task SerializeAsync(MqttDisconnectPacket packet, IMqttCommunicationChannel destination)
         {
             return SerializeEmptyPacketAsync(MqttControlPacketType.Disconnect, destination);
@@ -495,17 +533,6 @@ namespace MQTTnet.Core.Serializer
             }
         }
 
-        private static async Task SerializeAsync(MqttPubRelPacket packet, IMqttCommunicationChannel destination)
-        {
-            using (var output = new MqttPacketWriter())
-            {
-                output.Write(packet.PacketIdentifier);
-
-                output.InjectFixedHeader(MqttControlPacketType.PubRel, 0x02);
-                await output.WriteToAsync(destination);
-            }
-        }
-
         private static Task SerializeAsync(MqttPubCompPacket packet, IMqttCommunicationChannel destination)
         {
             using (var output = new MqttPacketWriter())
diff --git a/MQTTnet.Core/Serializer/MqttPacketWriter.cs b/MQTTnet.Core/Serializer/MqttPacketWriter.cs
index 4e2a3cb..778f52e 100644
--- a/MQTTnet.Core/Serializer/MqttPacketWriter.cs
+++ b/MQTTnet.Core/Serializer/MqttPacketWriter.cs
@@ -9,13 +9,13 @@ namespace MQTTnet.Core.Serializer
 {
     public sealed class MqttPacketWriter : IDisposable
     {
-        private readonly MemoryStream _buffer = new MemoryStream(512);
+        private readonly MemoryStream _buffer = new MemoryStream(1024);
 
         public void InjectFixedHeader(MqttControlPacketType packetType, byte flags = 0)
         {
-            var fixedHeader = (byte)((byte)packetType << 4);
+            var fixedHeader = (int)packetType << 4;
             fixedHeader |= flags;
-            InjectFixedHeader(fixedHeader);
+            InjectFixedHeader((byte)fixedHeader);
         }
 
         public void Write(byte value)
diff --git a/MQTTnet.Core/Serializer/MqttProtocolVersion.cs b/MQTTnet.Core/Serializer/MqttProtocolVersion.cs
new file mode 100644
index 0000000..6b8814a
--- /dev/null
+++ b/MQTTnet.Core/Serializer/MqttProtocolVersion.cs
@@ -0,0 +1,8 @@
+namespace MQTTnet.Core.Serializer
+{
+    public enum MqttProtocolVersion
+    {
+        V311,
+        V310
+    }
+}
diff --git a/MQTTnet.Core/Server/ConnectedMqttClient.cs b/MQTTnet.Core/Server/ConnectedMqttClient.cs
new file mode 100644
index 0000000..d363351
--- /dev/null
+++ b/MQTTnet.Core/Server/ConnectedMqttClient.cs
@@ -0,0 +1,11 @@
+using MQTTnet.Core.Serializer;
+
+namespace MQTTnet.Core.Server
+{
+    public class ConnectedMqttClient
+    {
+        public string ClientId { get; set; }
+
+        public MqttProtocolVersion ProtocolVersion { get; set; }
+    }
+}
diff --git a/MQTTnet.Core/Server/IMqttServer.cs b/MQTTnet.Core/Server/IMqttServer.cs
index 0b91c26..7a75624 100644
--- a/MQTTnet.Core/Server/IMqttServer.cs
+++ b/MQTTnet.Core/Server/IMqttServer.cs
@@ -9,7 +9,7 @@ namespace MQTTnet.Core.Server
         event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
         event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
 
-        IList<string> GetConnectedClients();
+        IList<ConnectedMqttClient> GetConnectedClients();
         void InjectClient(string identifier, IMqttCommunicationAdapter adapter);
         void Publish(MqttApplicationMessage applicationMessage);
         void Start();
diff --git a/MQTTnet.Core/Server/MqttClientSession.cs b/MQTTnet.Core/Server/MqttClientSession.cs
index a3919f9..bd99fe3 100644
--- a/MQTTnet.Core/Server/MqttClientSession.cs
+++ b/MQTTnet.Core/Server/MqttClientSession.cs
@@ -21,7 +21,6 @@ namespace MQTTnet.Core.Server
         private readonly MqttServerOptions _options;
 
         private CancellationTokenSource _cancellationTokenSource;
-        private IMqttCommunicationAdapter _adapter;
         private string _identifier;
         private MqttApplicationMessage _willApplicationMessage;
 
@@ -36,7 +35,9 @@ namespace MQTTnet.Core.Server
 
         public string ClientId { get; }
 
-        public bool IsConnected => _adapter != null;
+        public bool IsConnected => Adapter != null;
+
+        public IMqttCommunicationAdapter Adapter { get; private set; }
 
         public async Task RunAsync(string identifier, MqttApplicationMessage willApplicationMessage, IMqttCommunicationAdapter adapter)
         {
@@ -47,7 +48,7 @@ namespace MQTTnet.Core.Server
             try
             {
                 _identifier = identifier;
-                _adapter = adapter;
+                Adapter = adapter;
                 _cancellationTokenSource = new CancellationTokenSource();
 
                 _messageQueue.Start(adapter);
@@ -73,7 +74,7 @@ namespace MQTTnet.Core.Server
 
                 _messageQueue.Stop();
                 _cancellationTokenSource.Cancel();
-                _adapter = null;
+                Adapter = null;
 
                 MqttTrace.Information(nameof(MqttClientSession), $"Client '{_identifier}': Disconnected.");
             }
@@ -102,12 +103,12 @@ namespace MQTTnet.Core.Server
         {
             if (packet is MqttSubscribePacket subscribePacket)
             {
-                return _adapter.SendPacketAsync(_subscriptionsManager.Subscribe(subscribePacket), _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(_subscriptionsManager.Subscribe(subscribePacket), _options.DefaultCommunicationTimeout);
             }
 
             if (packet is MqttUnsubscribePacket unsubscribePacket)
             {
-                return _adapter.SendPacketAsync(_subscriptionsManager.Unsubscribe(unsubscribePacket), _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(_subscriptionsManager.Unsubscribe(unsubscribePacket), _options.DefaultCommunicationTimeout);
             }
 
             if (packet is MqttPublishPacket publishPacket)
@@ -122,7 +123,7 @@ namespace MQTTnet.Core.Server
 
             if (packet is MqttPubRecPacket pubRecPacket)
             {
-                return _adapter.SendPacketAsync(pubRecPacket.CreateResponse<MqttPubRelPacket>(), _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(pubRecPacket.CreateResponse<MqttPubRelPacket>(), _options.DefaultCommunicationTimeout);
             }
 
             if (packet is MqttPubAckPacket || packet is MqttPubCompPacket)
@@ -133,7 +134,7 @@ namespace MQTTnet.Core.Server
 
             if (packet is MqttPingReqPacket)
             {
-                return _adapter.SendPacketAsync(new MqttPingRespPacket(), _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(new MqttPingRespPacket(), _options.DefaultCommunicationTimeout);
             }
 
             if (packet is MqttDisconnectPacket || packet is MqttConnectPacket)
@@ -153,13 +154,16 @@ namespace MQTTnet.Core.Server
             if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
             {
                 _publishPacketReceivedCallback(this, publishPacket);
+                return Task.FromResult(0);
             }
-            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+
+            if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
             {
                 _publishPacketReceivedCallback(this, publishPacket);
-                return _adapter.SendPacketAsync(new MqttPubAckPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(new MqttPubAckPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
             }
-            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
+
+            if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
             {
                 // QoS 2 is implement as method "B" [4.3.3 QoS 2: Exactly once delivery]
                 lock (_unacknowledgedPublishPackets)
@@ -169,10 +173,10 @@ namespace MQTTnet.Core.Server
 
                 _publishPacketReceivedCallback(this, publishPacket);
 
-                return _adapter.SendPacketAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+                return Adapter.SendPacketAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
             }
 
-            throw new MqttCommunicationException("Received not supported QoS level.");
+            throw new MqttCommunicationException("Received a not supported QoS level.");
         }
 
         private Task HandleIncomingPubRelPacketAsync(MqttPubRelPacket pubRelPacket)
@@ -182,7 +186,7 @@ namespace MQTTnet.Core.Server
                 _unacknowledgedPublishPackets.Remove(pubRelPacket.PacketIdentifier);
             }
 
-            return _adapter.SendPacketAsync(new MqttPubCompPacket { PacketIdentifier = pubRelPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+            return Adapter.SendPacketAsync(new MqttPubCompPacket { PacketIdentifier = pubRelPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
         }
     }
 }
diff --git a/MQTTnet.Core/Server/MqttClientSessionsManager.cs b/MQTTnet.Core/Server/MqttClientSessionsManager.cs
index f78be0a..6165143 100644
--- a/MQTTnet.Core/Server/MqttClientSessionsManager.cs
+++ b/MQTTnet.Core/Server/MqttClientSessionsManager.cs
@@ -34,6 +34,9 @@ namespace MQTTnet.Core.Server
                     throw new MqttProtocolViolationException("The first packet from a client must be a 'CONNECT' packet [MQTT-3.1.0-1].");
                 }
 
+                // Switch to the required protocol version before sending any response.
+                eventArgs.ClientAdapter.PacketSerializer.ProtocolVersion = connectPacket.ProtocolVersion;
+
                 var connectReturnCode = ValidateConnection(connectPacket);
                 if (connectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
                 {
@@ -73,11 +76,15 @@ namespace MQTTnet.Core.Server
             }
         }
 
-        public IList<string> GetConnectedClients()
+        public IList<ConnectedMqttClient> GetConnectedClients()
         {
             lock (_syncRoot)
             {
-                return _clientSessions.Where(s => s.Value.IsConnected).Select(s => s.Key).ToList();
+                return _clientSessions.Where(s => s.Value.IsConnected).Select(s => new ConnectedMqttClient
+                {
+                    ClientId = s.Value.ClientId,
+                    ProtocolVersion = s.Value.Adapter.PacketSerializer.ProtocolVersion
+                }).ToList();
             }
         }
 
diff --git a/MQTTnet.Core/Server/MqttServer.cs b/MQTTnet.Core/Server/MqttServer.cs
index 98543b6..231cfcf 100644
--- a/MQTTnet.Core/Server/MqttServer.cs
+++ b/MQTTnet.Core/Server/MqttServer.cs
@@ -25,7 +25,7 @@ namespace MQTTnet.Core.Server
             _clientSessionsManager.ApplicationMessageReceived += (s, e) => ApplicationMessageReceived?.Invoke(s, e);
         }
 
-        public IList<string> GetConnectedClients()
+        public IList<ConnectedMqttClient> GetConnectedClients()
         {
             return _clientSessionsManager.GetConnectedClients();
         }
diff --git a/MQTTnet.sln b/MQTTnet.sln
index 697f504..c17884c 100644
--- a/MQTTnet.sln
+++ b/MQTTnet.sln
@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26430.15
+VisualStudioVersion = 15.0.26430.16
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Core.Tests", "Tests\MQTTnet.Core.Tests\MQTTnet.Core.Tests.csproj", "{A7FF0C91-25DE-4BA6-B39E-F54E8DADF1CC}"
 EndProject
@@ -27,6 +27,11 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Build", "Build", "{67C28AC1
 		Build\MQTTnet.nuspec = Build\MQTTnet.nuspec
 	EndProjectSection
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B3F60ECB-45BA-4C66-8903-8BB89CA67998}"
+	ProjectSection(SolutionItems) = preProject
+		README.md = README.md
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
diff --git a/README.md b/README.md
index 5df9d0f..4668d6c 100644
--- a/README.md
+++ b/README.md
@@ -5,40 +5,47 @@
 [![NuGet Badge](https://buildstats.info/nuget/MQTTnet)](https://www.nuget.org/packages/MQTTnet)
 
 # MQTTnet
-MQTTnet is a .NET library for MQTT based communication. It provides a MQTT client and a MQTT server. The implementation is based on the documentation from http://mqtt.org/.
+MQTTnet is a .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker). The implementation is based on the documentation from http://mqtt.org/.
 
-## Features
-* MQTT client included
-* MQTT server (broker) included
-* TLS 1.2 support for client and server (but not UWP servers)
+# Features
+
+## General
 * Async support
-* Rx support (via another project)
-* List of connected clients available (server only)
+* TLS 1.2 support for client and server (but not UWP servers)
 * Extensible communication channels (i.e. In-Memory, TCP, TCP+SSL, WebSockets (not included in this project))
-* Server is able to publish its own messages (no loopback client required)
+* Interfaces included for mocking and testing
+* Lightweight (only the low level implementation of MQTT, no overhead)
 * Access to internal trace messages
-* Extensible client credential validation (server only)
 * Unit tested (50+ tests)
-* Lightweight (only the low level implementation of MQTT, no overhead)
-* Interfaces included for mocking and testing
 
-## Supported frameworks
+## Client
+* Rx support (via another project)
+
+## Server (broker)
+* List of connected clients available
+* Supports connected clients with different protocol versions at the same time
+* Able to publish its own messages (no loopback client required)
+* Able to receive every messages (no loopback client required)
+* Extensible client credential validation
+
+# Supported frameworks
 * .NET Standard 1.3+
 * .NET Core 1.1+
 * .NET Core App 1.1+
 * .NET Framework 4.5.2+ (x86, x64, AnyCPU)
 * Universal Windows (UWP) 10.0.10240+ (x86, x64, ARM, AnyCPU)
 
-## Supported MQTT versions
+# Supported MQTT versions
 * 3.1.1
+* 3.1.0
 
-## Nuget
+# Nuget
 This library is available as a nuget package: https://www.nuget.org/packages/MQTTnet/
 
-## Contributions
+# Contributions
 If you want to contribute to this project just create a pull request.
 
-## References
+# References
 This library is used in the following projects:
 
 * MQTT Client Rx (Wrapper for Reactive Extensions, https://github.com/1iveowl/MQTTClient.rx)
@@ -46,8 +53,8 @@ This library is used in the following projects:
 
 If you use this library and want to see your project here please let me know.
 
-# MqttClient
-## Example
+# Examples
+## MqttClient
 
 ```csharp
 var options = new MqttClientOptions
@@ -119,9 +126,7 @@ while (true)
 }
 ```
 
-# MqttServer
-
-## Example 
+## MqttServer
 
 ```csharp
 var options = new MqttServerOptions
diff --git a/Tests/MQTTnet.Core.Tests/MQTTnet.Core.Tests.csproj b/Tests/MQTTnet.Core.Tests/MQTTnet.Core.Tests.csproj
index 62ddb72..88bf8f2 100644
--- a/Tests/MQTTnet.Core.Tests/MQTTnet.Core.Tests.csproj
+++ b/Tests/MQTTnet.Core.Tests/MQTTnet.Core.Tests.csproj
@@ -86,7 +86,7 @@
   <ItemGroup>
     <Compile Include="ByteReaderTests.cs" />
     <Compile Include="ByteWriterTests.cs" />
-    <Compile Include="DefaultMqttV311PacketSerializerTests.cs" />
+    <Compile Include="MqttPacketSerializerTests.cs" />
     <Compile Include="MqttServerTests.cs" />
     <Compile Include="MqttSubscriptionsManagerTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
diff --git a/Tests/MQTTnet.Core.Tests/DefaultMqttV311PacketSerializerTests.cs b/Tests/MQTTnet.Core.Tests/MqttPacketSerializerTests.cs
similarity index 92%
rename from Tests/MQTTnet.Core.Tests/DefaultMqttV311PacketSerializerTests.cs
rename to Tests/MQTTnet.Core.Tests/MqttPacketSerializerTests.cs
index 62d0f30..c03fa7a 100644
--- a/Tests/MQTTnet.Core.Tests/DefaultMqttV311PacketSerializerTests.cs
+++ b/Tests/MQTTnet.Core.Tests/MqttPacketSerializerTests.cs
@@ -12,8 +12,23 @@ using MQTTnet.Core.Serializer;
 namespace MQTTnet.Core.Tests
 {
     [TestClass]
-    public class DefaultMqttV311PacketSerializerTests
+    public class MqttPacketSerializerTests
     {
+        [TestMethod]
+        public void SerializeV310_MqttConnectPacket()
+        {
+            var p = new MqttConnectPacket
+            {
+                ClientId = "XYZ",
+                Password = "PASS",
+                Username = "USER",
+                KeepAlivePeriod = 123,
+                CleanSession = true
+            };
+
+            SerializeAndCompare(p, "EB0ABE1RSXNkcAPCAHsAA1hZWgAEVVNFUgAEUEFTUw==", MqttProtocolVersion.V310);
+        }
+
         [TestMethod]
         public void SerializeV311_MqttConnectPacket()
         {
@@ -96,6 +111,17 @@ namespace MQTTnet.Core.Tests
             SerializeAndCompare(p, "IAIBBQ==");
         }
 
+        [TestMethod]
+        public void SerializeV310_MqttConnAckPacket()
+        {
+            var p = new MqttConnAckPacket
+            {
+                ConnectReturnCode = MqttConnectReturnCode.ConnectionAccepted
+            };
+
+            SerializeAndCompare(p, "IAIAAA==", MqttProtocolVersion.V310);
+        }
+
         [TestMethod]
         public void DeserializeV311_MqttConnAckPacket()
         {
@@ -403,9 +429,9 @@ namespace MQTTnet.Core.Tests
             }
         }
 
-        private void SerializeAndCompare(MqttBasePacket packet, string expectedBase64Value)
+        private void SerializeAndCompare(MqttBasePacket packet, string expectedBase64Value, MqttProtocolVersion protocolVersion = MqttProtocolVersion.V311)
         {
-            var serializer = new DefaultMqttV311PacketSerializer();
+            var serializer = new MqttPacketSerializer { ProtocolVersion = protocolVersion };
             var channel = new TestChannel();
             serializer.SerializeAsync(packet, channel).Wait();
             var buffer = channel.ToArray();
@@ -415,7 +441,7 @@ namespace MQTTnet.Core.Tests
 
         private void DeserializeAndCompare(MqttBasePacket packet, string expectedBase64Value)
         {
-            var serializer = new DefaultMqttV311PacketSerializer();
+            var serializer = new MqttPacketSerializer();
 
             var channel1 = new TestChannel();
             serializer.SerializeAsync(packet, channel1).Wait();
diff --git a/Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs b/Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs
index 35bd92d..c8c6da6 100644
--- a/Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs
+++ b/Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs
@@ -4,6 +4,7 @@ using System.Threading.Tasks;
 using MQTTnet.Core.Adapter;
 using MQTTnet.Core.Client;
 using MQTTnet.Core.Packets;
+using MQTTnet.Core.Serializer;
 
 namespace MQTTnet.Core.Tests
 {
@@ -13,6 +14,8 @@ namespace MQTTnet.Core.Tests
 
         public TestMqttCommunicationAdapter Partner { get; set; }
 
+        public IMqttPacketSerializer PacketSerializer { get; } = new MqttPacketSerializer();
+
         public async Task ConnectAsync(MqttClientOptions options, TimeSpan timeout)
         {
             await Task.FromResult(0);