diff --git a/S7.Net/COTP.cs b/S7.Net/COTP.cs
new file mode 100644
index 0000000..432cffc
--- /dev/null
+++ b/S7.Net/COTP.cs
@@ -0,0 +1,94 @@
+using System;
+using System.IO;
+using System.Net.Sockets;
+
+namespace S7.Net
+{
+
+    /// <summary>
+    /// COTP Protocol functions and types
+    /// </summary>
+    internal class COTP
+    {
+        /// <summary>
+        /// Describes a COTP TPDU (Transport protocol data unit)
+        /// </summary>
+        public class TPDU
+        {
+            public byte HeaderLength;
+            public byte PDUType;
+            public int TPDUNumber;
+            public byte[] Data;
+            public bool LastDataUnit;
+
+            public TPDU(TPKT tPKT)
+            {
+                var br = new BinaryReader(new MemoryStream(tPKT.Data));
+                HeaderLength = br.ReadByte();
+                if (HeaderLength >= 2)
+                {
+                    PDUType = br.ReadByte();
+                    if (PDUType == 0xf0) //DT Data
+                    {
+                        var flags = br.ReadByte();
+                        TPDUNumber = flags & 0x7F;
+                        LastDataUnit = (flags & 0x80) > 0;
+                        Data = br.ReadBytes(tPKT.Length - HeaderLength - 4); //4 = TPKT Size
+                        return;
+                    }
+                    //TODO: Handle other PDUTypes
+                }
+                Data = new byte[0];
+            }
+
+            /// <summary>
+            /// Reads COTP TPDU (Transport protocol data unit) from the network stream
+            /// See: https://tools.ietf.org/html/rfc905
+            /// </summary>
+            /// <param name="socket">The socket to read from</param>
+            /// <returns>COTP DPDU instance</returns>
+            public static TPDU Read(Socket socket)
+            {
+                var tpkt = TPKT.Read(socket);
+                return new TPDU(tpkt);
+            }
+
+            public override string ToString()
+            {
+                return string.Format("Length: {0} PDUType: {1} TPDUNumber: {2} Last: {3} Segment Data: {4}",
+                    HeaderLength,
+                    PDUType,
+                    TPDUNumber,
+                    LastDataUnit,
+                    BitConverter.ToString(Data)
+                    );
+            }
+
+        }
+
+        /// <summary>
+        /// Describes a COTP TSDU (Transport service data unit). One TSDU consist of 1 ore more TPDUs
+        /// </summary>
+        public class TSDU
+        {
+            /// <summary>
+            /// Reads the full COTP TSDU (Transport service data unit)
+            /// See: https://tools.ietf.org/html/rfc905
+            /// </summary>
+            /// <returns>Data in TSDU</returns>
+            public static byte[] Read(Socket socket)
+            {                
+                var segment = TPDU.Read(socket);
+                var output = new MemoryStream(segment.Data.Length);
+                output.Write(segment.Data, 0, segment.Data.Length);
+
+                while (!segment.LastDataUnit)
+                {
+                    segment = TPDU.Read(socket);
+                    output.Write(segment.Data, (int)output.Position, segment.Data.Length);
+                }
+                return output.GetBuffer();
+            }
+        }
+    }
+}
diff --git a/S7.Net/PLC.cs b/S7.Net/PLC.cs
index ba2df55..6d2c0fe 100644
--- a/S7.Net/PLC.cs
+++ b/S7.Net/PLC.cs
@@ -39,6 +39,11 @@ namespace S7.Net
         /// Slot of the CPU of the PLC
         /// </summary>
         public Int16 Slot { get; private set; }
+
+        /// <summary>
+        /// Max PDU size this cpu supports
+        /// </summary>
+        public Int16 MaxPDUSize { get; private set; }
         
         /// <summary>
         /// Returns true if a connection to the PLC can be established
@@ -158,7 +163,6 @@ namespace S7.Net
         /// <returns>Returns ErrorCode.NoError if the connection was successful, otherwise check the ErrorCode</returns>
         public ErrorCode Open()
         {
-            byte[] bReceive = new byte[256];
 
             _mSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
             _mSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 1000);
@@ -243,28 +247,33 @@ namespace S7.Net
                         return ErrorCode.WrongCPU_Type;
                 }
 
+                //COTP Setup
                 _mSocket.Send(bSend1, 22, SocketFlags.None);
-                if (_mSocket.Receive(bReceive, 22, SocketFlags.None) != 22)
+                var response = COTP.TPDU.Read(_mSocket);
+                if (response.PDUType != 0xd0) //Connect Confirm
                 {
                     throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
-                } 
+                }
 
+                //S7ComSetup
                 byte[] bsend2 = { 3, 0, 0, 25, 2, 240, 128, 50, 1, 0, 0, 255, 255, 0, 8, 0, 0, 240, 0, 0, 3, 0, 3, 1, 0 };
                 _mSocket.Send(bsend2, 25, SocketFlags.None);
 
-                if (_mSocket.Receive(bReceive, 27, SocketFlags.None) != 27)
+                var s7data = COTP.TSDU.Read(_mSocket);
+                if (s7data.Length >= 2 && s7data[1] == 0x03) //Check for S7 Ack Data
                 {
-                    throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
-                } 
+                    MaxPDUSize = (short)(s7data[18] * 256 + s7data[19]);
+                    return ErrorCode.NoError;
+                }
+
+                throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
             }
-            catch(Exception exc)
+            catch (Exception exc)
             {
                 LastErrorCode = ErrorCode.ConnectionError;
                 LastErrorString = string.Format("Couldn't establish the connection to {0}.\nMessage: {1}", IP, exc.Message);
                 return ErrorCode.ConnectionError;
             }
-
-            return ErrorCode.NoError;
         }
 
         /// <summary>
@@ -290,11 +299,12 @@ namespace S7.Net
         public void ReadMultipleVars(List<DataItem> dataItems)
         {
             int cntBytes = dataItems.Sum(dataItem => VarTypeToByteLength(dataItem.VarType, dataItem.Count));
-            
-            if (dataItems.Count > 20)
-                throw new Exception("Too many vars requested");
-            if (cntBytes > 222)
-                throw new Exception("Too many bytes requested"); // TODO: proper TDU check + split in multiple requests
+
+            //Is this really a limit?
+            //if (dataItems.Count > 20) 
+            //    throw new Exception("Too many vars requested");
+            if (cntBytes > MaxPDUSize - 18)
+                throw new Exception(string.Format("Too many bytes requested Requested: {0} Max {1}", cntBytes, MaxPDUSize)); //TODO: split in multiple requests
 
             try
             {
@@ -310,12 +320,10 @@ namespace S7.Net
 
                 _mSocket.Send(package.array, package.array.Length, SocketFlags.None);
 
-                byte[] bReceive = new byte[512];
-                int numReceived = _mSocket.Receive(bReceive, 512, SocketFlags.None);
-                if (bReceive[21] != 0xff)
-                    throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
+                var s7data = COTP.TSDU.Read(_mSocket);
+                if (s7data[14] != 0xff) throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
 
-                int offset = 25;
+                int offset = 18;
                 foreach (var dataItem in dataItems)
                 {
                     int byteCnt = VarTypeToByteLength(dataItem.VarType, dataItem.Count);
@@ -323,7 +331,7 @@ namespace S7.Net
 
                     for (int i = 0; i < byteCnt; i++)
                     {
-                        bytes[i] = bReceive[i + offset];
+                        bytes[i] = s7data[i + offset];
                     }
 
                     offset += byteCnt + 4;
@@ -358,7 +366,7 @@ namespace S7.Net
             int index = startByteAdr;
             while (count > 0)
             {
-                var maxToRead = (int)Math.Min(count, 200);
+                var maxToRead = (int)Math.Min(count, MaxPDUSize);
                 byte[] bytes = ReadBytesWithASingleRequest(dataType, db, index, maxToRead);
                 if (bytes == null)
                     return resultBytes.ToArray();
@@ -636,7 +644,7 @@ namespace S7.Net
             int count = value.Length;
             while (count > 0)
             {
-                var maxToWrite = (int)Math.Min(count, 200);
+                var maxToWrite = (int)Math.Min(count, MaxPDUSize);
                 ErrorCode lastError = WriteBytesWithASingleRequest(dataType, db, startByteAdr + localIndex, value.Skip(localIndex).Take(maxToWrite).ToArray());
                 if (lastError != ErrorCode.NoError)
                 {
@@ -1063,13 +1071,12 @@ namespace S7.Net
 
                 _mSocket.Send(package.array, package.array.Length, SocketFlags.None);
 
-                byte[] bReceive = new byte[512];
-                int numReceived = _mSocket.Receive(bReceive, 512, SocketFlags.None);
-                if (bReceive[21] != 0xff)
+                var s7data = COTP.TSDU.Read(_mSocket);
+                if (s7data[14] != 0xff)
                     throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
 
                 for (int cnt = 0; cnt < count; cnt++)
-                    bytes[cnt] = bReceive[cnt + 25];
+                    bytes[cnt] = s7data[cnt + 25];
 
                 return bytes;
             }
@@ -1129,8 +1136,8 @@ namespace S7.Net
 
                 _mSocket.Send(package.array, package.array.Length, SocketFlags.None);
 
-                int numReceived = _mSocket.Receive(bReceive, 512, SocketFlags.None);
-                if (bReceive[21] != 0xff)
+                var s7data = COTP.TSDU.Read(_mSocket);
+                if (s7data[14] != 0xff)
                 {
                     throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
                 }
@@ -1179,11 +1186,9 @@ namespace S7.Net
 
                 _mSocket.Send(package.array, package.array.Length, SocketFlags.None);
 
-                int numReceived = _mSocket.Receive(bReceive, 512, SocketFlags.None);
-                if (bReceive[21] != 0xff)
-                {
+                var s7data = COTP.TSDU.Read(_mSocket);
+                if (bReceive[14] != 0xff)
                     throw new Exception(ErrorCode.WrongNumberReceivedBytes.ToString());
-                }
 
                 return ErrorCode.NoError;
             }
diff --git a/S7.Net/S7.Net.csproj b/S7.Net/S7.Net.csproj
index ac2ac19..bb2abab 100644
--- a/S7.Net/S7.Net.csproj
+++ b/S7.Net/S7.Net.csproj
@@ -77,9 +77,11 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Conversion.cs" />
+    <Compile Include="COTP.cs" />
     <Compile Include="Enums.cs" />
     <Compile Include="PLC.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="TPKT.cs" />
     <Compile Include="Types\Bit.cs" />
     <Compile Include="Types\Boolean.cs" />
     <Compile Include="Types\Byte.cs" />
diff --git a/S7.Net/TPKT.cs b/S7.Net/TPKT.cs
new file mode 100644
index 0000000..f5a4aab
--- /dev/null
+++ b/S7.Net/TPKT.cs
@@ -0,0 +1,46 @@
+using System;
+using System.Net.Sockets;
+
+namespace S7.Net
+{
+
+    /// <summary>
+    /// Describes a TPKT Packet
+    /// </summary>
+    internal class TPKT
+    {
+        public byte Version;
+        public byte Reserved1;
+        public int Length;
+        public byte[] Data;
+
+        /// <summary>
+        /// Reds a TPKT from the socket
+        /// </summary>
+        /// <param name="socket">The socket to read from</param>
+        /// <returns>TPKT Instace</returns>
+        public static TPKT Read(Socket socket)
+        {
+            var buf = new byte[4];
+            socket.Receive(buf, 4, SocketFlags.None);
+            var pkt = new TPKT
+            {
+                Version = buf[0],
+                Reserved1 = buf[1],
+                Length = buf[2] * 256 + buf[3] //BigEndian
+            };
+            pkt.Data = new byte[pkt.Length - 4];
+            socket.Receive(pkt.Data, pkt.Length - 4, SocketFlags.None);
+            return pkt;
+        }
+
+        public override string ToString()
+        {
+            return string.Format("Version: {0} Length: {1} Data: {2}",
+                Version,
+                Length,
+                BitConverter.ToString(Data)
+                );
+        }
+    }
+}