' MainForm
 
Public Class MainForm
    Private WithEvents myServer as New Server(nPort)
 
    [...]
 
    Private Sub StartServer()
        myServer.Start()
    End Sub
 
    [...]
End Class

' Server
 
Public Class Server
    Private tcpListener As TcpListener
    Private tcpClient As TcpClient
    Private nPort As Integer
 
    Public htUsers As New Hashtable(50) ' browsable by user
    Public htConnections As New Hashtable(50) ' browsable by connection
 
    Private thrListener As Thread
    Private ServerRunning As Boolean = False
 
    Sub New(ByVal Port As Integer)        
        nPort = Port
    End Sub
 
    Public Sub Start()
        tcpListener = New TcpListener(IPAddress.Any, nPort)
        tcpListener.Start()
        ServerRunning = True
        thrListener = New Thread(AddressOf KeepListening)
        thrListener.Start()
    End Sub
 
    Private Sub KeepListening()
        While ServerRunning
            tcpClient = tcpListener.AcceptTcpClient
            Dim newConnection As Connection = New Connection(tcpClient)
        End While
    End Sub
 
   [...]
End Class
 
 
' Connection
 
Class Connection
    Private Server As Server
    Private tcpClient As TcpClient
    Private thrSender As Thread
    Private srReceiver As StreamReader
    Private swSender As StreamWriter
    Private currentUser As String
    Private strResponse As String
 
    Sub New(ByVal tcpCon As TcpClient)
        tcpClient = tcpCon
 
        thrSender = New Thread(AddressOf AcceptClient)
        thrSender.Start()
    End Sub
 
    Public Sub CloseConnection()
        tcpClient.Close()
        srReceiver.Close()
        swSender.Close()
    End Sub
 
    Private Sub AcceptClient()
        srReceiver = New StreamReader(tcpClient.GetStream)
        swSender = New StreamWriter(tcpClient.GetStream)
 
        currentUser = Mid(CType(tcpClient.Client.RemoteEndPoint, _
          IPEndPoint).ToString, 1, _
                          InStr(CType(tcpClient.Client.RemoteEndPoint, _
                          IPEndPoint).ToString, _
                          ":") - 1) & ": " & srReceiver.ReadLine
 
        If Not currentUser = "" Then
            [...]
        Else
            CloseConnection()
        End If
 
        Try
            While True
                strResponse = srReceiver.ReadLine
                If strResponse Is Nothing Then
                    Server.RemoveUser(tcpClient)
                    Exit While
                Else
                    Select Case strResponse
                        [...]
                    End Select
                End If
            End While
        Catch ex As Exception
            [...]
        End Try
    End Sub
End Class